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February 4th, 1850.

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Work was just starting

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at the Hague Street Printing Press
in New York City.

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But, in the basement, temperatures
inside their coal-fired boiler

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were reaching dangerous levels.

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A force of nature
was struggling to break free.

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At 7:45, a huge explosion
tore the building apart.

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Dozens were killed
and many more injured.

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The boiler had overheated
and exploded.

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00:00:55,628 --> 00:00:58,300
Disasters like this
were happening daily

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during the Industrial Revolution.

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We'd begun to harness energy,

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but we were struggling
to control it with any precision.

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It's perhaps not surprising.

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After all, what is energy?

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Such an intangible thing to measure
and understand.

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In this series, I've been
exploring how we use measurement

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to quantify every aspect
of our world,

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creating a system of seven
fundamental units which

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have become the building blocks
of modern science.

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From time and distance,
to temperature and mass.

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I want to understand how we've
imposed order on the universe

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with these basic units
of measurement

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and how, through history,
each step forward in precision

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has unleashed
a technological revolution.

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This programme is all about energy,

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a difficult and dangerous force
that comes in many forms.

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The quest to describe
this mysterious power

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with a few simple units has been a
challenge for the greatest of minds.

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But it has also had
the most profound consequences

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for the way we live.

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This is the story of light, heat,
and electricity.

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Hundreds of kilometres
above our heads,

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a fleet of satellites
watch over the Earth.

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What they can do seems
almost magical, beyond belief.

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They can measure the thickness
of sea ice

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with millimetre accuracy...

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..measure the temperature
of our oceans

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or the subsidence of your house.

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And all of this is only possible

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because of our precise ability
to measure energy.

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Harnessing the power of light,
heat and electricity

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has transformed our lives in ways
no-one could have predicted.

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But how did we learn to measure
energy with such precision?

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Until the late 17th century,

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no-one really understood anything
about energy.

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Heat was considered
a strange, invisible fluid.

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Electricity, a frightening and
incomprehensible force of nature.

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And light?

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Something God-given
that shone down from the heavens

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and ripened our crops.

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# Gloria, gloria!

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♪ Gloria, gloria! ♪

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It took the brilliance
of Isaac Newton

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to revolutionise
the understanding of energy,

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making the intangible tangible.

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And it started with light.

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The year was 1665 and, as the plague
took hold of Britain,

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Newton fled his rooms
at the University of Cambridge

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for the safety
of his country retreat.

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He came here to
Woolsthorpe Manor in Lincolnshire.

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And it's here that it's thought
that he came up with a series

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of experiments that would change the
way we think about light for ever.

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At the time of Newton's experiments,

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it was well known that if you pass
light through a prism like this,

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then a spectrum of colour
is produced.

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But what most people thought

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was that somehow the prism
was colouring the light,

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but Newton thought differently.

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He wrote in a letter
to the Royal Society,

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"Having darkened my chamber, I made
a small hole in my window shuts

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"to let in a convenient quantity
of the sun's light.

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"I place my prism at his entrance."

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Now, to prove that it isn't the
prism that's colouring the light,

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Newton had a brilliant idea.

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What he did was to isolate
one of the colours

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and he did that using a screen.

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I'm going to pick out the green.

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Now, if it was the prism
that was colouring the light,

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if I put a second prism
in front of this green,

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it should change the colour.

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But when Newton did that,

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what he saw was
the same green colour on the wall.

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It wasn't the prism
that was colouring the light.

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Newton had proved
that it was the sunlight

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that was made up of
all of these different colours.

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He'd unearthed the secrets
behind the visible light spectrum.

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His account continued.

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"Light is a confused
aggregate of rays,

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"imbued with all sorts of colours.

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"The blue flame of brimstone,

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"the yellow flame of a candle,

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"and the various colours
of the fixed stars."

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Light was now something
that could be analysed.

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Solving its mysteries would allow
light to be manipulated

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and, most importantly of all,
measured.

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Hypersensitive
and extremely secretive,

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for years Newton didn't mention
the experiment to anyone.

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But, finally, in 1672,
he submitted his first formal paper

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about the experiment
to the Royal Society.

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When it was read to the fellows,

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it was met both with singular
attention, and uncommon applause.

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This experiment sowed the seeds
for the Age of Enlightenment.

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The age of science.

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When Newton discovered
the visible light spectrum,

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what he didn't realise

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was that there was also light
that he couldn't see.

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And we call it infrared.

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Over 100 years
after Newton's discovery,

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astronomer William Herschel
stumbled upon these invisible rays.

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Experimenting with
the visible light spectrum,

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Herschel began
taking the temperature

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of all the different colours.

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To his astonishment, when he placed
the thermometer beyond the red,

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the mercury began to rise.

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I've got a much more sensitive
thermometer here,

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called a thermocouple.

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You can see on the screen,
which is measuring the temperature,

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there's a sudden surge
out beyond the red.

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There we go.
There's the spike. Wow!

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Herschel called these
invisible rays "calorific rays",

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but we know them today as infrared.

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And in fact, all the waves -

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infrared, radio waves, X-rays,
microwaves, gamma rays -

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they're all, like visible light,

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certain forms
of electromagnetic radiation.

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And all of this
electromagnetic radiation

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are made up of photons of light
of different wavelengths,

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some which we can see,
and some which we can't.

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And it's the measurement
of these invisible ways

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which is at the heart
of 21st-century measurement.

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If light is made up of wavelengths
of photons, what is heat?

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For millennia,
this question remained a mystery.

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But its nature can best be seen
using a heat-sensitive camera.

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If I take this piece of wood
and hit it with a hammer...

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..then the infrared camera is
picking up a change in temperature.

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It's getting hotter.

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So the mechanical energy
of the hammer

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is causing an increase in heat.

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To understand
what is happening in the wood,

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I've come to meet
heat expert Michael de Podesta.

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Heat is the motion of molecules.

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Everything around you right now -

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inside it, the atoms and molecules
are moving very, very fast.

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Each of those fat globules is being
bombarded by the atoms around it.

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OK. So I can't see the atoms,

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but what I'm seeing
is the effect that those atoms,

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and the heat, which is the movement
of those atoms,

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has on the globules of fat.

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Exactly so.

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Heat is a type of energy.

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It's the energy that's tied up
in the motion of the particles

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but temperature
is a measure of their speed.

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Right. So actually
when I touch something,

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and I'm detecting how hot it is,
what I'm really detecting

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is how fast the molecules
are moving on the surface.

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That is exactly what
you are detecting.

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It's astonishing.

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To get to this molecular
understanding of temperature,

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we first had to go through
hundreds of years of experimentation

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and invention.

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And it all started in Renaissance
Italy in the 16th century.

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("Symphony No. 94, 'Surprise' "
by Joseph Haydn plays)

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Using touch or seeing how
the colour of something changes

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as you heat it up

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was about the only way we knew
how to measure temperature

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for thousands of years.

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An accurate temperature measurement
remained elusive

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until a breakthrough
was made here in Italy

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towards the end of the 16th century.

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And that moment came from
the father of modern physics,

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Galileo Galilei.

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He revolutionised
so many different areas -

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astronomy, physics, mechanics
and my own subject of mathematics.

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But, for me, the really big surprise

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is that Galileo
was one of the first

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to come up with
a way of measuring temperature.

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At the time, he was reading
a recently translated text

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by an ancient Greek mathematician
and engineer, Hero of Alexandria.

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And it's thought that Hero's ideas

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inspired Galileo
to look at temperature.

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Galileo invented what was then
called the thermoscope.

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It was wildly inaccurate, but it
was the world's first thermometer.

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A friend observed Galileo's
ground-breaking experiment.

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"He took a small glass flask
about as large as a small hen's egg

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"with a neck about two spans long
and as fine as a wheat straw...

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"..and warmed the flask
well in his hand.

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"When he took away the heat
of his hands from the flask,

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"the water at once began to rise
in the neck."

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What Galileo was exploiting here
was the fact that,

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if you heat something up,
like air, it expands.

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So the level of the water goes down.

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If I take my hands off,

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and let the flask cool down...

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..suddenly the level

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starts to go up again.

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00:13:08,516 --> 00:13:12,404
So suddenly we had the first
way of measuring the temperature,

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00:13:12,404 --> 00:13:14,564
instead using our hands or our eyes.

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00:13:19,316 --> 00:13:21,692
Intrigued by
the practical possibilities

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00:13:21,692 --> 00:13:26,444
of temperature measurement,
esteemed physician Santorio Santorio

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00:13:26,444 --> 00:13:28,604
began making his own thermoscopes.

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00:13:32,276 --> 00:13:35,300
He'd noticed that
when his patients were feverish

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they felt hotter than usual
and he wanted a way to prove it.

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00:13:40,484 --> 00:13:44,804
He gave the thermoscope a scale,
and, for the first time,

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00:13:44,804 --> 00:13:47,612
recorded the temperature
of a patient's mouth.

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00:13:49,556 --> 00:13:53,228
But because it was open-ended,
it was highly inaccurate,

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00:13:53,228 --> 00:13:56,252
the results varying
according to local air pressure.

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00:13:58,196 --> 00:13:59,708
Over the next few years,

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00:13:59,708 --> 00:14:03,164
Florence became a hotbed
for thermometer experimentation.

210
00:14:05,324 --> 00:14:09,428
In 1657, the Medici family set up
and funded

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00:14:09,428 --> 00:14:15,044
the Accademia del Cimento, known
as the Academy of Experimentation.

212
00:14:15,044 --> 00:14:19,148
Their motto was
"proving and proving again"

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00:14:19,148 --> 00:14:21,956
and temperature measurement
was all the rage.

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00:14:27,652 --> 00:14:30,892
It was a real fusion of art
and science,

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00:14:30,892 --> 00:14:34,484
using the skills of some of the
finest glass blowers in the world.

216
00:14:37,724 --> 00:14:40,748
Thermometers became
increasingly accurate.

217
00:14:40,748 --> 00:14:45,932
Water was replaced with alcohol
and the stems became sealed.

218
00:14:45,932 --> 00:14:51,980
Designer Segredo built circular
thermometers with 360 divisions.

219
00:14:51,980 --> 00:14:55,220
An idea he borrowed
from the ancient Babylonians,

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00:14:55,220 --> 00:14:58,676
who were the first
to divide circles into degrees.

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00:14:58,676 --> 00:15:02,564
It's why today we measure
temperature in degrees.

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00:15:08,396 --> 00:15:11,204
Having a thermometer
became the height of fashion

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00:15:11,204 --> 00:15:12,932
for any thinking man.

224
00:15:12,932 --> 00:15:15,740
The intangible had become tangible.

225
00:15:18,764 --> 00:15:20,924
By the end of the 18th century,

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00:15:20,924 --> 00:15:24,380
we didn't really understand
what temperature was.

227
00:15:24,380 --> 00:15:26,972
But we did have
a means of measuring it.

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00:15:26,972 --> 00:15:29,996
As for light, the opposite was true.

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00:15:29,996 --> 00:15:34,100
We understood what it was
but we couldn't measure it.

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00:15:34,100 --> 00:15:37,556
However, the study of the other
great form of energy,

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00:15:37,556 --> 00:15:40,148
electricity, was in its infancy.

232
00:15:44,684 --> 00:15:46,844
For thousands of years,

233
00:15:46,844 --> 00:15:49,652
lightning and strange tales
of torpedo rays

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00:15:49,652 --> 00:15:53,756
were the only manifestations of this
awesome force that we knew about.

235
00:15:57,644 --> 00:16:00,236
Striking fear into our hearts,

236
00:16:00,236 --> 00:16:04,340
all we could do was observe its
blinding light and its searing heat.

237
00:16:05,636 --> 00:16:10,172
Before the 18th century, we had
little idea what electricity was.

238
00:16:11,684 --> 00:16:15,572
We'd only puzzle over
the effects of static electricity,

239
00:16:15,572 --> 00:16:18,164
marvel at the destructive
power of lightning.

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00:16:20,972 --> 00:16:25,076
So, how did we come to exploit
and measure it so precisely?

241
00:16:29,828 --> 00:16:33,068
To answer that question,
we have to go back 300 years

242
00:16:33,068 --> 00:16:35,660
to a world
that was dark, cold and quiet.

243
00:16:35,660 --> 00:16:38,684
When the working day was
determined by when the sun set,

244
00:16:38,684 --> 00:16:40,628
letters were delivered
by horseback

245
00:16:40,628 --> 00:16:43,516
and electricity was just
a spectacle, performed by showmen,

246
00:16:43,516 --> 00:16:45,676
who called themselves electricians.

247
00:16:47,324 --> 00:16:50,348
But this was also a time
when people were becoming

248
00:16:50,348 --> 00:16:52,940
increasingly inquisitive
about their world.

249
00:16:54,884 --> 00:16:57,044
The 18th century
was a remarkable period

250
00:16:57,044 --> 00:16:58,772
in the history of measurement.

251
00:16:58,772 --> 00:17:00,716
This was
the Age of the Enlightenment,

252
00:17:00,716 --> 00:17:03,956
when scientists were looking at the
world around them with a keen eye,

253
00:17:03,956 --> 00:17:05,764
trying to find rational explanations

254
00:17:05,764 --> 00:17:08,924
for the phenomenon
that they observed.

255
00:17:08,924 --> 00:17:13,244
And the strange force of electricity
was coming under scrutiny.

256
00:17:18,212 --> 00:17:21,236
The breakthrough was made here
in Pavia in Northern Italy.

257
00:17:21,236 --> 00:17:24,476
It was made by a charismatic
and brilliant young scientist

258
00:17:24,476 --> 00:17:25,772
called Alessandro Volta.

259
00:17:25,772 --> 00:17:28,580
He became obsessed
with the seemingly magical power

260
00:17:28,580 --> 00:17:30,604
of electricity.

261
00:17:30,604 --> 00:17:33,980
In a state of deep emotional
distress, after a torrid love affair

262
00:17:33,980 --> 00:17:36,572
with a beautiful opera singer
called Mariana,

263
00:17:36,572 --> 00:17:38,948
the lovesick Volta threw himself

264
00:17:38,948 --> 00:17:42,052
into the investigation
of animal electricity.

265
00:17:43,996 --> 00:17:48,020
And the animal
he studied was the torpedo ray -

266
00:17:48,020 --> 00:17:51,476
a fish capable
of electrocuting its prey.

267
00:17:56,012 --> 00:17:57,956
What Volta was intrigued by was,

268
00:17:57,956 --> 00:18:02,492
what was inside the torpedo ray that
was causing this electrical shock?

269
00:18:02,492 --> 00:18:04,220
When he looked inside its anatomy,

270
00:18:04,220 --> 00:18:06,164
what he found was a column of cells

271
00:18:06,164 --> 00:18:08,756
that seemed to be responsible
for the shock.

272
00:18:08,756 --> 00:18:11,132
This is what he tried to copy.

273
00:18:12,428 --> 00:18:15,452
Volta must have played around
with many different ideas,

274
00:18:15,452 --> 00:18:20,420
trying things, nothing worked, until
suddenly he had a breakthrough.

275
00:18:20,420 --> 00:18:23,956
His lead came from the work
of Luigi Galvani.

276
00:18:23,956 --> 00:18:27,116
Attaching copper and iron wires
to a dead frog,

277
00:18:27,116 --> 00:18:31,004
Galvani discovered that he could
make its legs twitch.

278
00:18:31,004 --> 00:18:35,756
He believed he'd found a strange
new force inside the frog.

279
00:18:35,756 --> 00:18:38,564
Volta's brilliance
was realising the phenomena

280
00:18:38,564 --> 00:18:42,236
was actually down to Galvani's
use of two different metals.

281
00:18:43,964 --> 00:18:48,500
Inspired, he set about recreating
the torpedo ray's cell column

282
00:18:48,500 --> 00:18:50,876
using alternating types of metal.

283
00:18:54,196 --> 00:18:57,356
First of all,
he took a copper metal plate,

284
00:18:57,356 --> 00:18:59,812
put that one down on the bottom
of the pile.

285
00:18:59,812 --> 00:19:03,836
And then, on top of that, he put
a metal plate made out of zinc.

286
00:19:04,916 --> 00:19:07,940
And then the next ingredient
was a piece of card

287
00:19:07,940 --> 00:19:09,884
soaked in a weak acid solution.

288
00:19:11,044 --> 00:19:14,420
And then that
gets put on top of the zinc.

289
00:19:15,500 --> 00:19:17,012
So that's our first cell,

290
00:19:17,012 --> 00:19:19,604
and then he's going to make copies
of these cells,

291
00:19:19,604 --> 00:19:24,140
build up this kind of pile, a
little bit like in the torpedo ray.

292
00:19:24,140 --> 00:19:27,596
Another piece of acid,
so that goes on there.

293
00:19:29,324 --> 00:19:30,404
To test this idea,

294
00:19:30,404 --> 00:19:34,508
what he did was to attach
a wire to the bottom copper plate,

295
00:19:34,508 --> 00:19:38,180
another wire to the top zinc plate,

296
00:19:38,180 --> 00:19:41,204
and then what he hoped was
he'd get an electrical shock

297
00:19:41,204 --> 00:19:43,148
if he joined these two together.

298
00:19:43,148 --> 00:19:46,388
To really test it,
he placed the two ends of the wire

299
00:19:46,388 --> 00:19:48,412
on his tongue
to actually feel the shock.

300
00:19:48,412 --> 00:19:52,004
Hopefully, I haven't made this
too powerful. Let's try it out.

301
00:19:54,164 --> 00:19:55,540
It's quite gentle,

302
00:19:55,540 --> 00:19:58,916
but there is definitely the taste
of a fizz of electricity.

303
00:19:58,916 --> 00:20:02,588
And the more cells I put on top
of this, the bigger the current.

304
00:20:02,588 --> 00:20:07,124
To prove that I'm not just acting,
I've got a little light bulb here.

305
00:20:07,124 --> 00:20:10,796
If I attach this
to one end of the wire,

306
00:20:10,796 --> 00:20:12,740
and then to the other, there we go.

307
00:20:14,252 --> 00:20:17,060
The light lights up.

308
00:20:17,060 --> 00:20:20,516
But what's amazing about this
is it's not just a spark

309
00:20:20,516 --> 00:20:24,484
of static electricity,
or the shock of the ray.

310
00:20:24,484 --> 00:20:29,156
This is a gentle, continuous
stream of electricity.

311
00:20:29,156 --> 00:20:33,476
This is the first time
this had ever been done.

312
00:20:35,500 --> 00:20:38,660
And this is what really gave birth
to the modern battery.

313
00:20:45,788 --> 00:20:49,756
In Volta's typical self-confident
and flamboyant way

314
00:20:49,756 --> 00:20:54,212
he toured the lecture halls,
showing off his great invention.

315
00:20:54,212 --> 00:20:57,020
Other scientists
latched on to the discovery,

316
00:20:57,020 --> 00:20:59,828
using the cells
in their own experiments.

317
00:21:03,068 --> 00:21:04,796
It would take hundreds of years

318
00:21:04,796 --> 00:21:07,388
before we fully understood
electricity,

319
00:21:07,388 --> 00:21:10,628
but Volta had begun
to unlock its secrets.

320
00:21:13,004 --> 00:21:18,188
Electricity, light and heat
were no longer supernatural forces

321
00:21:18,188 --> 00:21:20,348
but tangible forms of energy

322
00:21:20,348 --> 00:21:25,532
that were attracting the greatest
minds in science to their study.

323
00:21:25,532 --> 00:21:28,772
And these scientists soon realised
better measurement

324
00:21:28,772 --> 00:21:32,444
would hold the key to harnessing
their immense power.

325
00:21:36,548 --> 00:21:39,356
By the time Volta
was creating the world's first

326
00:21:39,356 --> 00:21:41,732
continuous electrical current,

327
00:21:41,732 --> 00:21:46,052
thermometers had already
been around for 200 years.

328
00:21:46,052 --> 00:21:49,724
But readings varied
depending on whose model you used.

329
00:21:51,452 --> 00:21:54,692
It took Polish-born scientist
Daniel Fahrenheit

330
00:21:54,692 --> 00:21:56,636
to make the first big leap

331
00:21:56,636 --> 00:21:59,876
in standardising
temperature measurement.

332
00:21:59,876 --> 00:22:04,844
He chose mercury as it expands more
uniformly than other liquids

333
00:22:04,844 --> 00:22:09,244
and is liquid
over a wide temperature range.

334
00:22:09,244 --> 00:22:13,268
But his real innovation
was to introduce two reliable

335
00:22:13,268 --> 00:22:16,372
and reproducible
fixed temperature points,

336
00:22:16,372 --> 00:22:19,748
so a scale could be calibrated.

337
00:22:19,748 --> 00:22:23,636
At the low end, he chose
the melting point of pure ice,

338
00:22:23,636 --> 00:22:25,796
at 32 degrees.

339
00:22:25,796 --> 00:22:28,388
And the upper end, 96,

340
00:22:28,388 --> 00:22:31,196
the temperature of human blood.

341
00:22:31,196 --> 00:22:34,732
This later changed to the more
practical boiling point of water,

342
00:22:34,732 --> 00:22:37,244
at 212.

343
00:22:37,244 --> 00:22:40,484
Anders Celsius simplified things,

344
00:22:40,484 --> 00:22:43,076
choosing a 100-degree scale,

345
00:22:43,076 --> 00:22:46,964
based on the boiling and freezing
points of water.

346
00:22:46,964 --> 00:22:49,556
His brilliance
was to calibrate his thermometers

347
00:22:49,556 --> 00:22:51,716
to standard atmospheric pressure,

348
00:22:51,716 --> 00:22:54,524
making them accurate
whatever the weather.

349
00:22:59,492 --> 00:23:02,300
Both scales are still used today.

350
00:23:02,300 --> 00:23:04,460
But it took
the Industrial Revolution

351
00:23:04,460 --> 00:23:06,188
to show up their limitations.

352
00:23:08,348 --> 00:23:11,804
As the demands for ever greater
accuracy and range grew,

353
00:23:11,804 --> 00:23:14,260
the Celsius
and Fahrenheit thermometers

354
00:23:14,260 --> 00:23:15,908
were simply not up to the job

355
00:23:15,908 --> 00:23:19,148
in the fast-evolving world
of heavy industry.

356
00:23:28,652 --> 00:23:32,972
By the end of the 19th century,
steam engines like this Watt engine

357
00:23:32,972 --> 00:23:35,780
were really driving
the Industrial Revolution.

358
00:23:38,588 --> 00:23:41,396
They were pumping down mines,
in distilleries,

359
00:23:41,396 --> 00:23:45,796
controlling the machines
in factories across the country.

360
00:23:45,796 --> 00:23:48,956
This extraordinary engine
at Papplewick will be pumping

361
00:23:48,956 --> 00:23:51,764
over a million and a half gallons
of water a day

362
00:23:51,764 --> 00:23:53,708
for the citizens of Nottingham.

363
00:24:01,268 --> 00:24:06,020
The six huge furnaces
would use 100 tonnes of coal a week,

364
00:24:06,020 --> 00:24:08,396
shovelled by a team of 14 men,

365
00:24:08,396 --> 00:24:11,204
working back-breaking shifts
around the clock.

366
00:24:13,364 --> 00:24:15,308
The temperature inside this furnace

367
00:24:15,308 --> 00:24:18,332
is getting to over
1,000 degrees centigrade.

368
00:24:18,332 --> 00:24:20,140
That's heating water at the back

369
00:24:20,140 --> 00:24:22,868
which turns into steam,
which, using some valves,

370
00:24:22,868 --> 00:24:25,028
drives the pumps
of the Watt engine.

371
00:24:30,860 --> 00:24:33,236
Now, the thing is,
when water turns into steam,

372
00:24:33,236 --> 00:24:36,044
the volume changes
by a factor of 1,600,

373
00:24:36,044 --> 00:24:38,284
and that's where
all the power comes from.

374
00:24:38,284 --> 00:24:41,876
Now, the pressure depends on
the temperature inside this furnace.

375
00:24:41,876 --> 00:24:45,548
Get that temperature wrong,
and the whole place blows sky-high.

376
00:24:48,572 --> 00:24:51,164
By the second half
of the 19th century,

377
00:24:51,164 --> 00:24:53,324
boilers were exploding at a rate

378
00:24:53,324 --> 00:24:56,428
of almost one every four days
in America alone.

379
00:24:58,508 --> 00:25:01,180
One of the worst incidents
was later called

380
00:25:01,180 --> 00:25:04,124
the "Titanic of the Mississippi".

381
00:25:07,148 --> 00:25:09,740
The American Civil War
had just finished

382
00:25:09,740 --> 00:25:11,684
and the steam ship Sultana,

383
00:25:11,684 --> 00:25:15,652
packed with newly-released Union
prisoners of war was returning home.

384
00:25:17,516 --> 00:25:22,484
At 2am on April 27th, 1865,

385
00:25:22,484 --> 00:25:26,372
her boilers exploded,
tearing the ship apart.

386
00:25:29,828 --> 00:25:33,284
Over 1,700 lost their lives,

387
00:25:33,284 --> 00:25:37,388
in what remains one of America's
worst maritime disasters.

388
00:25:40,628 --> 00:25:45,380
Steam power was changing our world
but at a high cost.

389
00:25:45,380 --> 00:25:49,268
Thermometers simply wouldn't work
at these high temperatures.

390
00:25:49,268 --> 00:25:51,212
The glass would break.

391
00:25:51,212 --> 00:25:54,452
And the Fahrenheit
and Celsius scales themselves

392
00:25:54,452 --> 00:25:57,260
were far too inaccurate
at recording temperatures

393
00:25:57,260 --> 00:25:59,932
so much higher than the boiling
and freezing points

394
00:25:59,932 --> 00:26:02,444
that they were based on.

395
00:26:02,444 --> 00:26:07,628
A new means of measuring high
temperatures was urgently needed.

396
00:26:07,628 --> 00:26:12,596
And the answer ultimately
came from an unlikely source.

397
00:26:12,596 --> 00:26:13,676
Electricity.

398
00:26:15,188 --> 00:26:18,860
The breakthrough came in 1820,
when a German scientist,

399
00:26:18,860 --> 00:26:23,180
Thomas Johann Seebeck,
realised that if he took two wires

400
00:26:23,180 --> 00:26:26,284
of different metals
and wound them round each other

401
00:26:26,284 --> 00:26:28,660
and put the two wires
inside the furnace...

402
00:26:30,956 --> 00:26:33,980
..then took a compass
and put it over the wires...

403
00:26:35,708 --> 00:26:38,516
..he discovered the needle
of the compass moved.

404
00:26:38,516 --> 00:26:43,052
There was a magnetic field
being caused by this wire.

405
00:26:43,052 --> 00:26:46,724
The difference in temperature
between the end inside the furnace,

406
00:26:46,724 --> 00:26:51,476
and this end here is causing
a difference in voltage potential,

407
00:26:51,476 --> 00:26:54,716
which is creating an electrical
current running through this.

408
00:26:54,716 --> 00:26:57,308
The electrical current
causes the magnetic field,

409
00:26:57,308 --> 00:26:59,036
and that's what's being picked up,

410
00:26:59,036 --> 00:27:02,060
when I put the compass
over the top of this.

411
00:27:02,060 --> 00:27:06,164
This simple observation is what
led to the creation of a device

412
00:27:06,164 --> 00:27:07,676
called a thermocouple.

413
00:27:09,620 --> 00:27:11,996
In fact, a modern day thermocouple

414
00:27:11,996 --> 00:27:15,100
can actually measure
this voltage difference.

415
00:27:15,100 --> 00:27:18,260
I can record that the heart
of the furnace is going up...

416
00:27:18,260 --> 00:27:19,556
900 degrees...

417
00:27:19,556 --> 00:27:23,228
Look! It's just topped over
1,000 there.

418
00:27:23,228 --> 00:27:24,956
And, for me, the amazing thing

419
00:27:24,956 --> 00:27:27,764
is that we're using the measurement
of electricity

420
00:27:27,764 --> 00:27:32,300
to actually find out what the
temperature is inside this furnace.

421
00:27:32,300 --> 00:27:35,540
But before we could fully harness
heat's power,

422
00:27:35,540 --> 00:27:39,212
we needed to understand
what heat really was.

423
00:27:42,236 --> 00:27:45,908
In the 18th century,
a popular theory among scientists

424
00:27:45,908 --> 00:27:48,500
was that heat
was an invisible liquid

425
00:27:48,500 --> 00:27:50,660
that flowed in hot substances.

426
00:27:55,196 --> 00:28:00,164
It took keen amateur scientist,
James Prescott Joule, in 1840,

427
00:28:00,164 --> 00:28:02,756
to start to unlock its mysteries.

428
00:28:04,700 --> 00:28:07,724
And it begins
in rather an unlikely place.

429
00:28:07,724 --> 00:28:08,884
A brewery.

430
00:28:12,476 --> 00:28:14,204
Rather fond of beer,

431
00:28:14,204 --> 00:28:17,444
Joule realised that accurate
temperature measurement

432
00:28:17,444 --> 00:28:21,980
was crucial to making a good pint
in the family brewery.

433
00:28:21,980 --> 00:28:24,436
He became so good
at measuring temperature,

434
00:28:24,436 --> 00:28:27,164
that he claimed you could measure it
to an accuracy

435
00:28:27,164 --> 00:28:30,620
of one two-hundredth
of a degree Fahrenheit.

436
00:28:30,620 --> 00:28:32,780
But he also worked out
something else,

437
00:28:32,780 --> 00:28:36,452
something that was crucial
for scientists to understand.

438
00:28:36,452 --> 00:28:41,204
He devised a simple experiment
that had an extraordinary result.

439
00:28:43,796 --> 00:28:45,820
Placing a paddle in a tank of water

440
00:28:45,820 --> 00:28:49,412
and turning it using the energy
of a falling weight,

441
00:28:49,412 --> 00:28:53,516
he found that the temperature
of the water went up.

442
00:28:53,516 --> 00:28:56,756
He also found that
if the weight fell from even higher,

443
00:28:56,756 --> 00:28:59,996
the water got even warmer.

444
00:28:59,996 --> 00:29:02,804
Joule had discovered
mechanical energy

445
00:29:02,804 --> 00:29:05,692
could be transferred into heat.

446
00:29:08,852 --> 00:29:11,012
It was a huge breakthrough.

447
00:29:11,012 --> 00:29:15,116
Heat wasn't an invisible fluid
but a form of energy.

448
00:29:16,628 --> 00:29:18,004
But, at the time,

449
00:29:18,004 --> 00:29:21,892
the scientific community
largely shunned his findings,

450
00:29:21,892 --> 00:29:25,348
refusing to believe
this middle-class brewer

451
00:29:25,348 --> 00:29:28,724
could have anything meaningful
to contribute to science.

452
00:29:28,724 --> 00:29:33,260
It took a chance meeting for Joule
to be taken seriously.

453
00:29:33,260 --> 00:29:35,204
On honeymoon in the French Alps,

454
00:29:35,204 --> 00:29:38,660
and still obsessed with
proving his theories of heat,

455
00:29:38,660 --> 00:29:42,980
Joule spent his time, not with his
wife, but at waterfalls,

456
00:29:42,980 --> 00:29:45,356
measuring the difference
in water temperature

457
00:29:45,356 --> 00:29:47,084
between the top and the bottom.

458
00:29:49,676 --> 00:29:51,836
It was here that he bumped into

459
00:29:51,836 --> 00:29:54,644
the world-renowned scientist
Lord Kelvin.

460
00:29:57,668 --> 00:30:01,556
Their friendship would revolutionise
our understanding of heat.

461
00:30:03,716 --> 00:30:06,524
Inspired by the work of Joule,

462
00:30:06,524 --> 00:30:09,844
Lord Kelvin set about devising
a new temperature scale.

463
00:30:12,788 --> 00:30:14,948
No longer
would temperature measurement

464
00:30:14,948 --> 00:30:17,540
be based on the boiling
and freezing points of water,

465
00:30:17,540 --> 00:30:21,428
but on the very nature
of heat itself - energy.

466
00:30:23,588 --> 00:30:25,964
Performing hundreds
of gas experiments,

467
00:30:25,964 --> 00:30:30,932
Kelvin's goal was to find the
coldest temperature in the universe

468
00:30:30,932 --> 00:30:34,604
and to use this
as the base for his new scale.

469
00:30:39,572 --> 00:30:42,164
This is liquid helium

470
00:30:42,164 --> 00:30:44,540
and all this movement
is caused by the molecules

471
00:30:44,540 --> 00:30:46,700
firing around inside it.

472
00:30:46,700 --> 00:30:51,236
But as the temperature drops,
something strange starts to happen.

473
00:30:51,236 --> 00:30:56,204
The molecules slow right down
until they virtually stop moving.

474
00:30:56,204 --> 00:31:02,036
The helium is close to a theoretical
temperature called absolute zero.

475
00:31:02,036 --> 00:31:08,084
Kelvin calculated this to
be minus 273 degrees Celsius,

476
00:31:08,084 --> 00:31:11,540
a temperature where molecules
no longer move.

477
00:31:11,540 --> 00:31:15,212
There is no energy
and therefore no heat.

478
00:31:16,724 --> 00:31:18,236
The inside of this flask

479
00:31:18,236 --> 00:31:21,692
is now one of the coldest places
in the universe.

480
00:31:24,068 --> 00:31:27,956
Using absolute zero
as the lower point of the scale,

481
00:31:27,956 --> 00:31:31,412
Kelvin had tied its base
to the nature of heat.

482
00:31:32,708 --> 00:31:34,652
Yet, to make the scale practical,

483
00:31:34,652 --> 00:31:38,540
what was needed
was a fixed point higher up.

484
00:31:38,540 --> 00:31:41,780
Kelvin died before his theories
were put into practice...

485
00:31:43,508 --> 00:31:46,316
..but the scientists
that followed in his footsteps

486
00:31:46,316 --> 00:31:50,420
chose a strange phenomena
called the triple point,

487
00:31:50,420 --> 00:31:53,444
where a substance
can exist simultaneously

488
00:31:53,444 --> 00:31:56,468
as a gas, liquid and a solid.

489
00:31:57,764 --> 00:32:01,868
The reason measurement scientists
like this triple point so much,

490
00:32:01,868 --> 00:32:06,404
is that it happens
at a very precise temperature.

491
00:32:06,404 --> 00:32:10,724
So, at this point, we see
the nitrogen in liquid and gas form.

492
00:32:13,612 --> 00:32:16,772
And we're going to reduce
the pressure.

493
00:32:16,772 --> 00:32:19,364
As the pressure drops,
so does the temperature,

494
00:32:19,364 --> 00:32:23,036
and the nitrogen
begins to solidify.

495
00:32:23,036 --> 00:32:25,412
And we should be able to get...
There we go.

496
00:32:27,220 --> 00:32:32,756
We've now captured the nitrogen in
both liquid, gaseous and solid form.

497
00:32:32,756 --> 00:32:37,940
You can see this solid kind of,
like, nitrogen ice sitting on top

498
00:32:37,940 --> 00:32:40,964
and the gas is bubbling underneath,
pushing the solid up,

499
00:32:40,964 --> 00:32:42,476
and the liquid below that.

500
00:32:44,284 --> 00:32:46,580
The old Fahrenheit
and Celsius scales

501
00:32:46,580 --> 00:32:49,820
were fixed to the boiling
and freezing points of water,

502
00:32:49,820 --> 00:32:52,196
which can vary enormously.

503
00:32:52,196 --> 00:32:55,436
The beauty of triple points
is that they never vary

504
00:32:55,436 --> 00:32:57,676
by more than
a few millionths of a degree.

505
00:32:59,324 --> 00:33:02,348
Now, with this idea of
a theoretical absolute zero,

506
00:33:02,348 --> 00:33:03,860
and these triple points

507
00:33:03,860 --> 00:33:07,100
corresponding to different
substances - nitrogen, water -

508
00:33:07,100 --> 00:33:11,204
finally the world had a precise
scale to measure temperature.

509
00:33:13,364 --> 00:33:14,444
Oh!

510
00:33:15,524 --> 00:33:19,628
Half a century after his death,
the kelvin was adopted

511
00:33:19,628 --> 00:33:23,300
as the international unit
of temperature measurement

512
00:33:23,300 --> 00:33:26,540
and tied to a fixed point
more accurate

513
00:33:26,540 --> 00:33:29,780
than Celsius and Fahrenheit
could ever have imagined -

514
00:33:29,780 --> 00:33:31,508
the triple point of water.

515
00:33:33,884 --> 00:33:37,772
With it, incredible feats
of engineering were now possible.

516
00:33:37,772 --> 00:33:41,228
From forging metals
to growing crystals,

517
00:33:41,228 --> 00:33:45,548
the world finally had
a temperature scale it could trust.

518
00:33:54,620 --> 00:33:59,372
Like heat, the story of electricity
also took a giant leap forward

519
00:33:59,372 --> 00:34:01,964
during the Industrial Revolution.

520
00:34:04,124 --> 00:34:08,308
It was French maths prodigy
and physicist André-Marie Ampère

521
00:34:08,308 --> 00:34:10,820
who was to make
the next real breakthrough.

522
00:34:12,764 --> 00:34:17,300
Intrigued with Ørsted's discoveries,
he decided to further investigate

523
00:34:17,300 --> 00:34:20,540
the relationship
between electricity and magnetism.

524
00:34:25,940 --> 00:34:28,100
Using apparatus
very similar to this,

525
00:34:28,100 --> 00:34:31,124
he discovered that if he passed
an electrical current

526
00:34:31,124 --> 00:34:32,852
between two parallel wires,

527
00:34:32,852 --> 00:34:36,092
it created a magnetic attraction
between them.

528
00:34:36,092 --> 00:34:38,684
Now, I've beefed up the experiment
a little bit

529
00:34:38,684 --> 00:34:42,788
by using these coils of wire, but if
I turn on the electrical current...

530
00:34:44,516 --> 00:34:47,972
..the coils are then
attracted to each other.

531
00:34:47,972 --> 00:34:51,644
And the key thing for us is
the greater the electrical current,

532
00:34:51,644 --> 00:34:53,588
so if I beef that up a bit...

533
00:34:54,884 --> 00:34:58,340
..the greater
the magnetic force between them.

534
00:35:00,284 --> 00:35:04,388
Ampère had found a new way
to measure electricity.

535
00:35:06,548 --> 00:35:09,140
By measuring the strength
of the magnetic force,

536
00:35:09,140 --> 00:35:12,812
he was able to build a machine
to measure current

537
00:35:12,812 --> 00:35:15,188
called a galvanometer,

538
00:35:15,188 --> 00:35:18,860
named in honour of electrical
pioneer Luigi Galvani.

539
00:35:21,532 --> 00:35:24,260
And there was a practical use
to all this.

540
00:35:24,260 --> 00:35:28,876
Ampère's work was about to pave
the way for modern communication.

541
00:35:32,252 --> 00:35:35,708
The first telegraph systems
were basically a wire

542
00:35:35,708 --> 00:35:38,084
with a galvanometer
stuck at each end.

543
00:35:41,756 --> 00:35:45,212
They worked by sending
pulses of current down a wire,

544
00:35:45,212 --> 00:35:47,668
which then deflected these needles.

545
00:35:50,180 --> 00:35:54,932
Messages could now be sent at a
speed of about six words per minute.

546
00:35:58,388 --> 00:36:00,412
But it took a grizzly murder

547
00:36:00,412 --> 00:36:04,220
for this new-fangled invention
to be taken seriously.

548
00:36:07,676 --> 00:36:13,292
In 1845, John Tawell
poisoned his lover, Sarah Hart,

549
00:36:13,292 --> 00:36:15,452
with a deadly drink of prussic acid.

550
00:36:18,476 --> 00:36:21,284
Fleeing the scene,
he jumped on a train to London.

551
00:36:23,740 --> 00:36:28,196
The alarm was raised and a telegraph
message sent to Paddington Station.

552
00:36:32,300 --> 00:36:35,324
"A murder has just been committed
at Salt Hill,

553
00:36:35,324 --> 00:36:38,564
"and the suspected murderer was
seen to take a first-class ticket

554
00:36:38,564 --> 00:36:42,668
"to London by the train
which left Slough at 7:42pm.

555
00:36:43,748 --> 00:36:46,124
"He is in the garb of a Quaker."

556
00:36:48,716 --> 00:36:51,604
The message took
ten minutes to get to London.

557
00:36:51,604 --> 00:36:53,684
The train took 50.

558
00:36:59,732 --> 00:37:03,836
On his arrival, Tawell was met
and tailed by a London bobby.

559
00:37:04,916 --> 00:37:09,668
News of his spectacular arrest
made every paper in the country.

560
00:37:09,668 --> 00:37:11,828
The power
of electrical communication

561
00:37:11,828 --> 00:37:13,772
was clear for all to see.

562
00:37:17,092 --> 00:37:21,116
Soon telegraph lines
were being laid across the world.

563
00:37:21,116 --> 00:37:24,356
A revolution in global
communications was underway.

564
00:37:25,732 --> 00:37:29,324
But with no international system
of measuring electricity,

565
00:37:29,324 --> 00:37:31,700
there were serious problems.

566
00:37:31,700 --> 00:37:36,020
If too much current was pushed down
the line, the wires caught fire.

567
00:37:36,020 --> 00:37:38,612
Too little and the message
never got through.

568
00:37:41,420 --> 00:37:45,524
With lots of competing
and different units
of electrical measurement in use,

569
00:37:45,524 --> 00:37:47,900
standardisation was urgently needed.

570
00:37:50,060 --> 00:37:54,812
And, in 1881, on the site
of the Grand Palais here in Paris,

571
00:37:54,812 --> 00:37:57,404
that dream would become a reality.

572
00:38:02,804 --> 00:38:04,964
It was at the First Congress
of Electricians,

573
00:38:04,964 --> 00:38:09,068
attended by 250 people
from 28 different countries,

574
00:38:09,068 --> 00:38:14,036
that the ampere, the volt, the ohm,
and the farad were finally defined.

575
00:38:14,036 --> 00:38:16,628
Ultimately, it would be the ampere

576
00:38:16,628 --> 00:38:19,868
that would become the international
unit for electricity.

577
00:38:21,028 --> 00:38:23,324
Finally, the world had a standard

578
00:38:23,324 --> 00:38:25,484
for accurately measuring
electricity.

579
00:38:25,484 --> 00:38:29,804
As the brains of the electrical
world met behind closed doors,

580
00:38:29,804 --> 00:38:32,044
the French public were being treated

581
00:38:32,044 --> 00:38:36,284
to the greatest exhibition
of electricity ever seen.

582
00:38:36,284 --> 00:38:38,660
All along the capital's
tree-lined avenues,

583
00:38:38,660 --> 00:38:41,980
and in the exhibition halls,
the latest electrical lighting,

584
00:38:41,980 --> 00:38:45,572
trams, telephones, generating
systems, signalling devices

585
00:38:45,572 --> 00:38:49,028
would have been gathered for the
congress and the whole world to see.

586
00:38:49,028 --> 00:38:51,620
It must have been
an extraordinary sight.

587
00:38:51,620 --> 00:38:56,156
In fact, onlookers described
it as a great blaze of splendour.

588
00:38:56,156 --> 00:38:58,532
It really marked
the spirit of the age -

589
00:38:58,532 --> 00:39:00,988
a spirit of innovation
and invention.

590
00:39:00,988 --> 00:39:04,580
But it was a young American engineer
and entrepreneur

591
00:39:04,580 --> 00:39:06,524
who stole the show that year.

592
00:39:08,684 --> 00:39:11,060
His name was Thomas Edison.

593
00:39:13,652 --> 00:39:17,540
In two enormous rooms,
filled with crystal chandeliers

594
00:39:17,540 --> 00:39:20,564
and hundreds upon hundreds
of lights,

595
00:39:20,564 --> 00:39:22,724
the crowds were dazzled and amazed.

596
00:39:24,668 --> 00:39:27,476
But the invention that caught
everyone's attention

597
00:39:27,476 --> 00:39:33,308
was his giant electrical generator,
capable of lighting 1,200 lamps.

598
00:39:35,252 --> 00:39:40,220
With it were plans for the first
complete electrical supply system.

599
00:39:40,220 --> 00:39:43,892
A system that would bring
together the power of heat,

600
00:39:43,892 --> 00:39:46,916
electricity and light
for the very first time.

601
00:39:48,428 --> 00:39:52,316
At its heart would be
a steam-driven power station

602
00:39:52,316 --> 00:39:54,692
that would supply enough electricity

603
00:39:54,692 --> 00:39:57,932
to light over 100 businesses
and private houses.

604
00:39:59,444 --> 00:40:02,252
Edison was about
to light up our world.

605
00:40:10,244 --> 00:40:13,916
Six months later, Edison's dream
would become a reality.

606
00:40:17,804 --> 00:40:20,396
On the 4th of September 1882,

607
00:40:20,396 --> 00:40:23,636
Edison switched on
his Pearl Street Power Station

608
00:40:23,636 --> 00:40:26,660
and electrical current started
flowing to 59 customers

609
00:40:26,660 --> 00:40:29,684
in Lower Manhattan,
powering 400 lamps.

610
00:40:31,492 --> 00:40:35,164
The newspapers reported how,
in a twinkling,

611
00:40:35,164 --> 00:40:38,756
the area bounded by Spruce, Wall,
Nassau and Pearl Streets

612
00:40:38,756 --> 00:40:39,836
was in a glow.

613
00:40:42,428 --> 00:40:45,452
It marked the dawn
of the electrical age.

614
00:40:46,964 --> 00:40:49,124
The world would never be
quite the same again.

615
00:40:49,124 --> 00:40:51,284
Electricity had arrived.

616
00:40:55,820 --> 00:40:59,356
And even Edison must have been
surprised by its popularity.

617
00:41:12,452 --> 00:41:13,964
Within two years,

618
00:41:13,964 --> 00:41:17,716
demand for Pearl Street electricity
had rocketed tenfold.

619
00:41:17,716 --> 00:41:20,660
Electricity soon became
a household commodity,

620
00:41:20,660 --> 00:41:23,252
like buying a load of coal
or a box of matches.

621
00:41:23,252 --> 00:41:25,196
At least, if you could afford it.

622
00:41:25,196 --> 00:41:26,708
The next great challenge

623
00:41:26,708 --> 00:41:29,084
was measuring how much people
were using.

624
00:41:30,596 --> 00:41:36,292
But the galvanometer and the units
defined in Paris couldn't do this.

625
00:41:36,292 --> 00:41:38,804
Edison could have
charged his customers

626
00:41:38,804 --> 00:41:41,396
based on
the number of lamps they had.

627
00:41:41,396 --> 00:41:45,716
But soon he realised this was not
a profitable way to do business.

628
00:41:47,444 --> 00:41:52,196
What he needed was a way to measure
current usage over time

629
00:41:52,196 --> 00:41:56,596
and his solution was to use
the principles of electroplating.

630
00:41:59,108 --> 00:42:04,292
Edison's first electricity meter
basically consisted of a glass jar

631
00:42:04,292 --> 00:42:10,124
with two copper plates suspended
in a copper sulphate solution.

632
00:42:10,124 --> 00:42:14,228
Now, as I pass electricity
through the cell,

633
00:42:14,228 --> 00:42:18,332
then what happens is that atoms
transfer from the solution

634
00:42:18,332 --> 00:42:21,572
onto the plate,
making the plate heavier.

635
00:42:24,164 --> 00:42:28,268
Now, the key point here
is the total mass of copper

636
00:42:28,268 --> 00:42:31,724
deposited on the plate
is directly proportional

637
00:42:31,724 --> 00:42:34,532
to the total current
running through the system.

638
00:42:34,532 --> 00:42:38,852
So now, if I switch off the
electricity and take the plate out,

639
00:42:38,852 --> 00:42:42,388
you can see here the copper
that's been deposited.

640
00:42:42,388 --> 00:42:45,764
Now, the amazing thing for me
is that instead of measuring

641
00:42:45,764 --> 00:42:47,924
this rather elusive property
of electricity,

642
00:42:47,924 --> 00:42:50,516
we're actually just
measuring a change in weight.

643
00:42:50,516 --> 00:42:53,108
Finally, Edison had a way
to charge his customers

644
00:42:53,108 --> 00:42:55,268
for the amount
of electricity they used.

645
00:42:55,268 --> 00:42:58,508
He'd send out one of his employees
to visit the cells.

646
00:42:58,508 --> 00:43:01,316
They'd take out the plate,
measure the change in weight,

647
00:43:01,316 --> 00:43:04,340
and the customers
would be billed accordingly.

648
00:43:04,340 --> 00:43:06,284
Now, it wasn't a brilliant system,

649
00:43:06,284 --> 00:43:07,660
but at least it was A system

650
00:43:07,660 --> 00:43:10,684
for measuring the amount of
electricity that had been used.

651
00:43:16,220 --> 00:43:18,812
While the measurement of heat
and electricity

652
00:43:18,812 --> 00:43:22,052
was making great advances
in the industrial era,

653
00:43:22,052 --> 00:43:25,372
the quest to measure light
had been all but forgotten.

654
00:43:26,804 --> 00:43:30,044
It took the emergence of street
lights to change all this.

655
00:43:31,772 --> 00:43:35,228
Before Edison lit up our world
using electricity,

656
00:43:35,228 --> 00:43:37,820
the very first lamps
were powered by gas.

657
00:43:41,356 --> 00:43:44,084
It was the beginning
of the 19th century -

658
00:43:44,084 --> 00:43:47,540
theft was on the rise
and murder was commonplace.

659
00:43:48,836 --> 00:43:51,644
There was a desperate need
for safer streets.

660
00:43:52,940 --> 00:43:57,476
And that came with the installation
of the first public gas lights

661
00:43:57,476 --> 00:43:59,852
here in Central London in 1807.

662
00:44:01,796 --> 00:44:05,684
Demand for this new-fangled
gas lighting soared

663
00:44:05,684 --> 00:44:08,708
and soon unscrupulous companies
were cashing in,

664
00:44:08,708 --> 00:44:12,380
selling low-quality gas
at high-quality prices.

665
00:44:12,380 --> 00:44:14,756
The outrage that ensued

666
00:44:14,756 --> 00:44:20,156
forced the government to introduce
a new measure for light intensity.

667
00:44:20,156 --> 00:44:23,396
It was called candlepower
and it was based on the brightness

668
00:44:23,396 --> 00:44:26,204
of a special candle
made out of beeswax

669
00:44:26,204 --> 00:44:31,604
and naturally occurring oil taken
from the head of a sperm whale -

670
00:44:31,604 --> 00:44:33,116
the spermaceti candle.

671
00:44:37,004 --> 00:44:42,188
The new unit was to be the light
produced by one spermaceti candle

672
00:44:42,188 --> 00:44:44,348
weighing one-sixth of a pound

673
00:44:44,348 --> 00:44:48,020
and burning at a rate
of 120 grains per hour.

674
00:44:49,964 --> 00:44:54,068
It was the world's first attempt to
try and produce a standard measure

675
00:44:54,068 --> 00:44:57,524
of light intensity
but it was still very arbitrary.

676
00:44:57,524 --> 00:45:00,764
Light inspectors would go out,
hold up greasy bits of paper,

677
00:45:00,764 --> 00:45:03,004
and try and compare
the brightness of light

678
00:45:03,004 --> 00:45:05,516
coming from gas lamps
to those of a candle.

679
00:45:05,516 --> 00:45:08,540
And it had a fundamental problem
that still haunts

680
00:45:08,540 --> 00:45:11,564
the measurement of light
intensity to this day.

681
00:45:11,564 --> 00:45:15,236
It depends entirely
on our own perception of light.

682
00:45:25,820 --> 00:45:29,572
Now, this is the light
produced by 100 candles.

683
00:45:29,572 --> 00:45:32,812
In a moment, I'm going
to extinguish 50 of them.

684
00:45:32,812 --> 00:45:37,484
The problem is that the pupil
in my eye expands and contracts

685
00:45:37,484 --> 00:45:40,372
to control the amount
of light entering them,

686
00:45:40,372 --> 00:45:43,100
which means that
when I extinguish half of them,

687
00:45:43,100 --> 00:45:45,556
it isn't going to look
half as bright.

688
00:45:58,652 --> 00:46:02,756
Now, although the camera is
recording a lower light condition,

689
00:46:02,756 --> 00:46:06,644
to my human eye, although I've got
half as many candles,

690
00:46:06,644 --> 00:46:09,020
this looks as bright
as it did before.

691
00:46:14,420 --> 00:46:18,524
It took a remarkable series
of experiments in the 1920s

692
00:46:18,524 --> 00:46:21,628
to solve the riddle
of human light perception.

693
00:46:23,492 --> 00:46:28,028
In an international study,
200 people aged 18 to 60

694
00:46:28,028 --> 00:46:30,620
underwent a series of tests

695
00:46:30,620 --> 00:46:33,644
to find out what colour wavelengths
we see best

696
00:46:33,644 --> 00:46:36,100
and how our eyes combine
these different colours

697
00:46:36,100 --> 00:46:38,396
to perceive brightness.

698
00:46:38,396 --> 00:46:42,284
Their work would lead to
the creation of the candela,

699
00:46:42,284 --> 00:46:44,660
the unit we use
to measure light today.

700
00:46:50,492 --> 00:46:53,084
Here at the
National Physical Laboratory,

701
00:46:53,084 --> 00:46:57,404
Dr Nigel Fox can show me
how unreliable my eyes are

702
00:46:57,404 --> 00:46:59,780
as a means of measurement.

703
00:46:59,780 --> 00:47:01,804
Yes, that's good. So let's measure.

704
00:47:01,804 --> 00:47:06,260
So, it looks a bit like
a '70s disco in here, but...

705
00:47:06,260 --> 00:47:11,444
Yes. Yes, we can't quite reproduce
the experiment of the 1920s.

706
00:47:11,444 --> 00:47:13,604
The equipment has all disappeared.

707
00:47:13,604 --> 00:47:15,332
But what we've tried to do

708
00:47:15,332 --> 00:47:17,924
is simulate the effect
of that experiment here.

709
00:47:17,924 --> 00:47:21,380
So, Marcus, which of those lights
looks the brightest to you?

710
00:47:25,268 --> 00:47:27,644
Well, I'd say
that the green one is...

711
00:47:27,644 --> 00:47:30,236
seems to be a lot brighter
than the red and the blue.

712
00:47:30,236 --> 00:47:34,124
The red and the blue. Maybe the blue
next and then the red third.

713
00:47:34,124 --> 00:47:36,716
But, yeah, the green
certainly seems the brightest.

714
00:47:36,716 --> 00:47:38,444
Well, would it surprise you

715
00:47:38,444 --> 00:47:40,820
if I said the green
is less than all of the others?

716
00:47:40,820 --> 00:47:44,060
Oh, really? Less intense? That's
right. So you're not tricking me?

717
00:47:44,060 --> 00:47:46,652
No, no. This is...
What's this recording?

718
00:47:46,652 --> 00:47:49,892
This instrument is measuring
the actual radiometric power

719
00:47:49,892 --> 00:47:52,916
that is coming from
those different light sources.

720
00:47:52,916 --> 00:47:56,372
And as the instruments prove,
my eyes really are deceiving me.

721
00:47:58,100 --> 00:47:59,612
That's extraordinary.

722
00:47:59,612 --> 00:48:02,852
The red is actually much more
powerful than the green,

723
00:48:02,852 --> 00:48:07,036
yet my eye is seeing the green
as more luminous. Exactly.

724
00:48:12,356 --> 00:48:14,516
The 1920s tests revealed

725
00:48:14,516 --> 00:48:16,892
not only that our eyes
were much more sensitive

726
00:48:16,892 --> 00:48:18,836
to yellowish-green light,

727
00:48:18,836 --> 00:48:20,564
but that our age and sex

728
00:48:20,564 --> 00:48:24,020
also affect how we perceive
the brightness of light.

729
00:48:25,532 --> 00:48:29,204
Compiling their results,
the scientists came up with

730
00:48:29,204 --> 00:48:32,228
an average human perception
of brightness.

731
00:48:32,228 --> 00:48:37,060
It's roughly equivalent to how
a woman in her late 20s sees light.

732
00:48:39,004 --> 00:48:41,516
To this day,
the definition of the candela

733
00:48:41,516 --> 00:48:43,892
remains locked to these findings.

734
00:48:46,916 --> 00:48:49,076
I can understand
the need for the candela.

735
00:48:49,076 --> 00:48:51,316
I mean, having
a unit of measurement

736
00:48:51,316 --> 00:48:55,124
which measures how the human eye
sees light is clearly useful.

737
00:48:55,124 --> 00:48:57,716
I mean, take this traffic light
that's coming up.

738
00:48:57,716 --> 00:49:00,388
I want to know that it's bright
enough that I'm going to see it

739
00:49:00,388 --> 00:49:02,900
but not so bright
that it's going to dazzle me.

740
00:49:02,900 --> 00:49:06,356
The same applies to
the car headlamps, street lamps,

741
00:49:06,356 --> 00:49:08,732
lights in our home -
the list is endless.

742
00:49:14,780 --> 00:49:17,156
Because it's based
on human perception,

743
00:49:17,156 --> 00:49:21,260
there's something rather odd
about the candela as a unit.

744
00:49:21,260 --> 00:49:25,364
I mean, it's kind of the black sheep
of the measurement family.

745
00:49:25,364 --> 00:49:28,172
And the candela's days are numbered.

746
00:49:29,548 --> 00:49:33,140
Today scientists are trying
to base all measurement

747
00:49:33,140 --> 00:49:37,244
on the fundamental,
unchanging laws of the universe.

748
00:49:37,244 --> 00:49:41,564
We've done it for the metre -
basing it on the speed of light.

749
00:49:41,564 --> 00:49:45,452
And the second - on the movement
of electrons inside an atom.

750
00:49:48,044 --> 00:49:53,012
Now the goal is to do the same
for heat, electricity and light.

751
00:50:02,300 --> 00:50:05,756
Today, just as during
the Industrial Revolution...

752
00:50:07,052 --> 00:50:09,860
..our ability to measure
these energy units

753
00:50:09,860 --> 00:50:12,668
is failing to keep up
with the demands of industry.

754
00:50:17,636 --> 00:50:20,876
Here at Rolls Royce,
measuring and harnessing heat

755
00:50:20,876 --> 00:50:24,196
at temperatures
higher than 2,000 degrees kelvin

756
00:50:24,196 --> 00:50:29,084
will help deliver more fuel-
efficient and powerful jet engines.

757
00:50:29,084 --> 00:50:32,324
Accurately measuring
very high temperatures

758
00:50:32,324 --> 00:50:34,484
is a huge technical challenge.

759
00:50:35,564 --> 00:50:37,940
This is the high pressure
turbine blade.

760
00:50:37,940 --> 00:50:40,316
This is the first rotating component

761
00:50:40,316 --> 00:50:44,420
that the gas stream would encounter,
coming down from the combustor.

762
00:50:44,420 --> 00:50:47,308
Whereabouts is that in here?
Are we downstream of the...?

763
00:50:47,308 --> 00:50:49,172
Downstream of the burners, yes.

764
00:50:49,172 --> 00:50:51,764
So this is exposed
to extreme temperatures.

765
00:50:51,764 --> 00:50:54,356
It is indeed, and temperatures
above its melting point.

766
00:50:54,356 --> 00:50:56,084
ABOVE its melting point?!

767
00:50:56,084 --> 00:50:59,108
So this would actually...
SHOULD be melting, then? But... OK.

768
00:50:59,108 --> 00:51:01,996
How do you make sure it doesn't
melt? We have to heavily cool them.

769
00:51:01,996 --> 00:51:05,156
So you can see
some of the features that do that.

770
00:51:05,156 --> 00:51:09,476
The holes on the surface, there
are passageways inside of the blade,

771
00:51:09,476 --> 00:51:12,068
finished items would have
a coating on them as well,

772
00:51:12,068 --> 00:51:14,444
a thermal barrier coating,

773
00:51:14,444 --> 00:51:17,764
a ceramic layer which also
takes a lot of the heat away.

774
00:51:17,764 --> 00:51:21,572
Despite state-of-the-art
thermocouples, computer modelling,

775
00:51:21,572 --> 00:51:24,164
and thermal paints
on the turbine blades,

776
00:51:24,164 --> 00:51:27,188
the experts here
can only achieve an accuracy

777
00:51:27,188 --> 00:51:28,996
of about four degrees kelvin.

778
00:51:30,940 --> 00:51:34,316
Better accuracy
isn't just a technical problem.

779
00:51:34,316 --> 00:51:37,340
The Kelvin scale itself
loses accuracy

780
00:51:37,340 --> 00:51:38,932
the higher temperatures get.

781
00:51:44,252 --> 00:51:46,196
Today, new technologies

782
00:51:46,196 --> 00:51:49,004
are pushing temperature measurement
to the absolute limit.

783
00:51:49,004 --> 00:51:52,028
Such that a new standard
is critically needed.

784
00:51:52,028 --> 00:51:55,564
Here at the NPL heat lab, they think
they might be close to cracking it.

785
00:51:59,156 --> 00:52:00,884
Michael de Podesta has built

786
00:52:00,884 --> 00:52:04,124
the most accurate thermometer
in the world,

787
00:52:04,124 --> 00:52:06,500
an acoustic gas thermometer.

788
00:52:09,740 --> 00:52:15,436
It's the culmination of a 150-year
story that began with Kelvin himself.

789
00:52:15,436 --> 00:52:18,164
What we are doing
is we're determining temperatures

790
00:52:18,164 --> 00:52:22,052
in terms of the speed
with which molecules are moving.

791
00:52:22,052 --> 00:52:24,428
What we measure is the speed of sound

792
00:52:24,428 --> 00:52:27,452
through argon gas trapped
in this container down here.

793
00:52:27,452 --> 00:52:30,908
It seems extraordinary
to be using sound,

794
00:52:30,908 --> 00:52:33,500
in a way,
to be measuring temperature.

795
00:52:33,500 --> 00:52:37,172
Well, if you think about
a sound wave,

796
00:52:37,172 --> 00:52:41,492
momentarily, gas is compressed
and that heats up the gas

797
00:52:41,492 --> 00:52:46,244
and the gas then springs back and
you're turning that thermal energy,

798
00:52:46,244 --> 00:52:49,348
the motion of... the microscopic
motion of the molecules,

799
00:52:49,348 --> 00:52:51,428
back into mechanical energy.

800
00:52:51,428 --> 00:52:54,884
So sound is directly
linked to temperature.

801
00:52:54,884 --> 00:52:58,124
So what we measure
is the speed of sound

802
00:52:58,124 --> 00:53:00,500
and what we can infer
very, very directly

803
00:53:00,500 --> 00:53:02,012
is the speed of the molecule.

804
00:53:10,004 --> 00:53:13,244
If it's successful,
the acoustic gas thermometer

805
00:53:13,244 --> 00:53:15,836
will be as revolutionary
for the measurement of heat

806
00:53:15,836 --> 00:53:17,996
as the atomic clock was for time.

807
00:53:17,996 --> 00:53:19,724
Just as Kelvin dreamt,

808
00:53:19,724 --> 00:53:21,884
it will create an absolute system

809
00:53:21,884 --> 00:53:24,692
based on one of the fundamental
constants of the universe,

810
00:53:24,692 --> 00:53:27,716
the Boltzmann constant -
a magical number

811
00:53:27,716 --> 00:53:31,604
which relates the movement
of molecules to temperature.

812
00:53:31,604 --> 00:53:36,004
When that happens, temperature
will join the metre and the second

813
00:53:36,004 --> 00:53:40,028
in being tied to
a universal constant of nature.

814
00:53:41,756 --> 00:53:45,428
And with it
will come incredible precision,

815
00:53:45,428 --> 00:53:49,100
with devices capable
of measuring accurately

816
00:53:49,100 --> 00:53:52,340
at temperatures
hotter than the surface of the sun.

817
00:53:54,932 --> 00:53:57,956
It will give us
greater control of heat,

818
00:53:57,956 --> 00:54:00,548
making engines more efficient
and economical.

819
00:54:05,516 --> 00:54:08,540
Incredibly, in a lab
just down the corridor

820
00:54:08,540 --> 00:54:12,644
from the acoustic thermometer,
another breakthrough is underway.

821
00:54:19,772 --> 00:54:22,364
Here, JT Janssen and his team

822
00:54:22,364 --> 00:54:25,604
are revolutionising
the measurement of electricity.

823
00:54:28,412 --> 00:54:32,084
And their work can be traced back
to Volta's battery experiment.

824
00:54:34,028 --> 00:54:37,916
We now know if you break something
down into its building blocks,

825
00:54:37,916 --> 00:54:42,020
atoms, you'll find
a positively-charged nucleus,

826
00:54:42,020 --> 00:54:45,260
orbited by
negatively-charged electrons.

827
00:54:46,772 --> 00:54:49,796
Metals like the copper and zinc
used by Volta

828
00:54:49,796 --> 00:54:54,116
have electrons that readily
detach from their nuclei.

829
00:54:54,116 --> 00:54:56,788
It is these loose-moving electrons

830
00:54:56,788 --> 00:55:00,380
that enable electricity to flow,
forming a current.

831
00:55:02,756 --> 00:55:05,564
Using some of the strongest magnets
on the planet

832
00:55:05,564 --> 00:55:09,020
and temperatures
close to absolute zero,

833
00:55:09,020 --> 00:55:13,556
JT's team are controlling
the movement of single electrons

834
00:55:13,556 --> 00:55:17,444
and counting them as they pass
through their experiment,

835
00:55:17,444 --> 00:55:19,604
one at a time.

836
00:55:19,604 --> 00:55:23,924
Well, we've been working on this
experiment for about ten years now.

837
00:55:23,924 --> 00:55:27,812
It's all related to trying
to redefine the ampere,

838
00:55:27,812 --> 00:55:29,836
the unit for electrical current,

839
00:55:29,836 --> 00:55:32,348
in terms of a fundamental
constant of nature

840
00:55:32,348 --> 00:55:35,588
and, in this case, that is the
charge of an individual electron.

841
00:55:35,588 --> 00:55:37,532
And now we are at the level

842
00:55:37,532 --> 00:55:40,852
where we can control
a billion electrons per second

843
00:55:40,852 --> 00:55:43,796
and we're only missing
a few of those.

844
00:55:43,796 --> 00:55:48,980
JT's experiment will redefine
our measure of electrical current

845
00:55:48,980 --> 00:55:51,788
using these individual electrons.

846
00:55:51,788 --> 00:55:56,972
They are fundamental particles,
the same throughout the universe.

847
00:55:56,972 --> 00:55:59,996
For scientists, this is the goal -

848
00:55:59,996 --> 00:56:04,100
tying measurement
to the unchanging laws of physics.

849
00:56:07,124 --> 00:56:11,012
And their work won't just impact
on the world of measurement.

850
00:56:11,012 --> 00:56:14,036
Controlling the flow
of single electrons

851
00:56:14,036 --> 00:56:17,276
is key
to developing quantum computers.

852
00:56:17,276 --> 00:56:19,868
This next generation of technology

853
00:56:19,868 --> 00:56:23,324
will produce computers
capable of calculations

854
00:56:23,324 --> 00:56:26,132
that are vastly beyond
what is currently possible.

855
00:56:27,212 --> 00:56:30,236
They could simulate the human brain,

856
00:56:30,236 --> 00:56:32,828
model climate change in real-time

857
00:56:32,828 --> 00:56:35,204
and data storage using electrons

858
00:56:35,204 --> 00:56:37,796
would mean virtually
limitless capacity.

859
00:56:41,900 --> 00:56:45,572
As we delve deeper
inside the fabric of our universe,

860
00:56:45,572 --> 00:56:49,460
into the quantum world
of subatomic particles,

861
00:56:49,460 --> 00:56:53,564
measurement is undergoing
a fundamental and exciting change.

862
00:56:56,588 --> 00:56:59,612
We are now using the very
building blocks of matter

863
00:56:59,612 --> 00:57:02,204
to help us measure
the world around us.

864
00:57:05,876 --> 00:57:08,468
Even the black sheep
of the measurement family,

865
00:57:08,468 --> 00:57:11,924
the candela,
could soon be redefined,

866
00:57:11,924 --> 00:57:14,516
tied to the flow
of photons of light.

867
00:57:20,132 --> 00:57:24,020
What started with our senses
and crude guesswork

868
00:57:24,020 --> 00:57:28,340
is now getting down to the smallest
building blocks of the universe,

869
00:57:28,340 --> 00:57:32,444
as our human urge for ever-greater
precision drives us forward.

870
00:57:35,900 --> 00:57:39,788
Measurement has changed the course
of science and civilisation.

871
00:57:41,380 --> 00:57:44,324
Now, as the quantum age approaches,

872
00:57:44,324 --> 00:57:46,780
our world is set
to change once more.

873
00:57:52,828 --> 00:57:56,852
This is all part of a story which
started thousands of years ago,

874
00:57:56,852 --> 00:58:02,468
when our ancestors began to
measure time, length and weight.

875
00:58:02,468 --> 00:58:05,276
They were trying to understand
the environment around them,

876
00:58:05,276 --> 00:58:08,084
to measure it
and, ultimately, to manipulate it.

877
00:58:10,108 --> 00:58:13,268
But isn't that really
what's still driving us today?

878
00:58:13,268 --> 00:58:15,428
Because measurement is the key

879
00:58:15,428 --> 00:58:18,668
to understanding
our place in the universe.