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00:00February 4th, 1850.
00:10Work was just starting at the Hay Street Printing Press in New York City.
00:15But in the basement, temperatures inside their coal-fired boiler were reaching dangerous levels.
00:23A force of nature was struggling to break free.
00:30At 7.45, a huge explosion tore the building apart.
00:41Dozens were killed and many more injured.
00:45The boiler had overheated and exploded.
00:49Disasters like this were happening daily during the Industrial Revolution.
01:01We'd begun to harness energy, but we were struggling to control it with any precision.
01:07It's perhaps not surprising.
01:11After all, what is energy?
01:14Such an intangible thing to measure and understand.
01:18In this series, I've been exploring how we use measurement to quantify every aspect of our world,
01:25creating a system of seven fundamental units which have become the building blocks of modern science.
01:32From time and distance to temperature and mass,
01:36I want to understand how we've imposed order on the universe with these basic units of measurement.
01:43And how, through history, each step forward in precision has unleashed a technological revolution.
01:49This program is all about energy, a difficult and dangerous force that comes in many forms.
01:59The quest to describe this mysterious power with a few simple units has been a challenge for the greatest of minds.
02:08But it has also had the most profound consequences for the way we live.
02:13This is the story of light, heat and electricity.
02:29Hundreds of kilometres above our heads, a fleet of satellites watch over the Earth.
02:38What they can do seems almost magical, beyond belief.
02:44They can measure the thickness of sea ice with millimetre accuracy.
02:51Measure the temperature of our oceans or the subsidence of your house.
02:57And all of this is only possible because of our precise ability to measure energy.
03:05Harnessing the power of light, heat and electricity
03:09has transformed our lives in ways no one could have predicted.
03:17But how did we learn to measure energy with such precision?
03:21Until the late 17th century, no-one really understood anything about energy.
03:34Heat was considered a strange, invisible fluid.
03:39Electricity, a frightening and incomprehensible force of nature.
03:43It took the brilliance of Isaac Newton to revolutionise the understanding of energy,
04:03making the intangible tangible, and it started with light.
04:10The year was 1665, and as the play took hold of Britain,
04:15Newton fled his rooms at the University of Cambridge
04:17for the safety of his country retreat.
04:20He came here to Walthorpe Manor in Lincolnshire,
04:23and it's here that it's thought that he came up with a series of experiments
04:28that would change the way we think about light forever.
04:40At the time of Newton's experiments,
04:42it was well known that if you pass light through a prism like this,
04:45then a spectrum of colour is produced.
04:47But what most people thought was that somehow the prism was colouring the light.
04:55But Newton thought differently.
05:03He wrote in a letter to the Royal Society,
05:05Having darkened my chamber, I made a small hole in my window shuts
05:10to let in a convenient quantity of the sun's light.
05:14I place my prism at his entrance.
05:25Now, to prove that it isn't the prism that's colouring the light,
05:29Newton had a brilliant idea.
05:32What he did was to isolate one of the colours,
05:35and he did that using a screen.
05:38I'm going to pick out the green.
05:40Now, if it was the prism that was colouring the light,
05:45if I put a second prism in front of this green,
05:48it should change the colour.
05:50But when Newton did that,
05:53what he saw was the same green colour on the wall.
05:57It wasn't the prism that was colouring the light.
06:04Newton had proved that it was the sunlight
06:06that was made up of all of these different colours.
06:09He'd unearthed the secrets behind the visible light spectrum.
06:16His account continued.
06:18Light is a confused aggregate of rays,
06:22imbued with all sorts of colours.
06:24The blue flame of brimstone,
06:27the yellow flame of a candle,
06:29and the various colours of the fixed stars.
06:35Light was now something that could be analysed.
06:39Solving its mysteries would allow light to be manipulated,
06:43and most importantly of all, measured.
06:51Hypersensitive and extremely secretive,
06:53for years Newton didn't mention the experiment to anyone.
06:56But finally, in 1672,
06:59he submitted his first formal paper about the experiment
07:01to the Royal Society.
07:04When it was read to the fellows,
07:05it was met both with singular attention
07:07and uncommon applause.
07:14This experiment sowed the seeds for the age of enlightenment,
07:19the age of science.
07:21When Newton discovered the visible light spectrum,
07:26what he didn't realise
07:28was that there was also light that he couldn't see.
07:32And we call it...
07:34Infrared.
07:36Over 100 years after Newton's discovery,
07:40astronomer William Herschel
07:42stumbled upon these invisible rays.
07:46Experimenting with the visible light spectrum,
07:48Herschel began taking the temperature
07:50of all the different colours.
07:53To his astonishment,
07:55when he placed the thermometer beyond the red,
07:57the mercury began to rise.
08:03So I've got a much more sensitive thermometer here,
08:08called a thermocouple,
08:08and you can see on the screen,
08:10which is measuring the temperature,
08:11there's a sudden surge out beyond the red.
08:14There we go.
08:16There's the spike.
08:16Wow.
08:19Herschel called these invisible rays calorific rays,
08:23but we know them today as infrared.
08:26And in fact,
08:27all the waves,
08:28infrared,
08:29radio waves,
08:30x-rays,
08:31microwaves,
08:32gamma rays,
08:33they're all, like visible light,
08:35certain forms of electromagnetic radiation.
08:37And all of this electromagnetic radiation
08:39are made up of photons of light,
08:42of different wavelengths,
08:43some which we can see
08:44and some which we can't.
08:46And it's the measurement of these invisible rays
08:49which is at the heart
08:50of 21st century measurement.
08:52If light is made up of wavelengths of photons,
09:01what is heat?
09:04For millennia,
09:05this question remained a mystery.
09:09But its nature can best be seen
09:11using a heat-sensitive camera.
09:14So if I take this piece of wood
09:15and hit it with a hammer,
09:18then the infrared camera
09:22is picking up a change in temperature.
09:24It's getting hotter.
09:25So the mechanical energy of the hammer
09:28is causing an increase in heat.
09:34To understand what is happening in the wood,
09:37I've come to meet heat expert,
09:39Michael de Podesta.
09:41Heat is the motion of molecules.
09:46Everything around you right now,
09:49inside it,
09:50the atoms and molecules are moving.
09:52They're moving very, very fast.
09:54Each of those fat globules
09:56is being bombarded by the atoms around it.
09:59OK, so I can't see the atoms,
10:01but what I'm seeing is the effect
10:03that those atoms and the heat,
10:05which is the movement of those atoms,
10:07has on the globules of fat.
10:09Exactly so.
10:11Heat is a type of energy.
10:12It's the energy that's tied up
10:14in the motion of the particles.
10:17But temperature is a measure of their speed.
10:20Right.
10:21So actually when I touch something
10:22and I'm actually detecting how hot it is,
10:25what I'm really detecting
10:26is how fast the molecules are moving on the surface.
10:29That is exactly what you're detecting.
10:32It's astonishing.
10:34To get to this molecular understanding of temperature,
10:38we first had to go through hundreds of years
10:40of experimentation and invention.
10:44And it all started in Renaissance Italy
10:46in the 16th century.
10:48Using touch or seeing how the colour of something changes
11:07as you heat it up
11:08was about the only way we knew how to measure temperature
11:11for thousands of years.
11:12An accurate temperature measurement remained elusive
11:15until a breakthrough was made here in Italy
11:18towards the end of the 16th century.
11:19And that moment came from the father of modern physics,
11:29Galileo Galilei.
11:32He revolutionised so many different areas.
11:35Astronomy, physics, mechanics,
11:37and my own subject of mathematics.
11:42But for me, the really big surprise
11:45is that Galileo was one of the first
11:47to come up with a way of measuring temperature.
11:52At the time, he was reading a recently translated text
11:56by an ancient Greek mathematician and engineer,
11:59Hero of Alexandria.
12:00And it's thought that Hero's ideas inspired Galileo
12:04to look at temperature.
12:06Galileo invented what was then called the thermoscope.
12:10It was wildly inaccurate,
12:13but it was the world's first thermometer.
12:16A friend observed Galileo's groundbreaking experiment.
12:22He took a small glass flask,
12:25about as large as a small hen's egg,
12:27with a neck about two spans long
12:29and as fine as a wheat straw
12:31and warmed the flask well in his hand.
12:38When he took away the heat of his hands from the flask,
12:42the water at once began to rise in the neck.
12:50What Galileo was exploiting here
12:52was the fact that if you heat something up,
12:54like air, it expands.
12:56So the level of the water goes down.
12:59And if I take my hands off
13:01and let the flask cool down,
13:05then suddenly the level starts to go up again.
13:08So suddenly we had the first way
13:10of measuring the temperature
13:12instead of using our hands or our eyes.
13:14Intrigued by the practical possibilities of temperature measurement,
13:23esteemed physician Santorio Santorio began making his own thermoscopes.
13:29He'd noticed that when his patients were feverish,
13:35they felt hotter than usual,
13:37and he wanted a way to prove it.
13:40He gave the thermoscope a scale
13:42and for the first time recorded the temperature of a patient's mouth.
13:48But because it was open-ended,
13:51it was highly inaccurate,
13:52the results varying according to local air pressure.
13:58Over the next few years,
14:00Florence became a hotbed for thermometer experimentation.
14:03In 1657, the Medici family set up and funded the Academia del Cimento,
14:11known as the Academy of Experimentation.
14:14Their motto was proving and proving again,
14:18and temperature measurement was all the rage.
14:21It was a real fusion of art and science,
14:30using the skills of some of the finest glassblowers in the world.
14:37Thermometers became increasingly accurate.
14:41Water was replaced with alcohol and the stems became sealed.
14:46Designer Sagredo built circular thermometers with 360 divisions.
14:51An idea he borrowed from the ancient Babylonians,
14:55who were the first to divide circles into degrees.
14:59It's why today we measure temperature in degrees.
15:08Having a thermometer became the height of fashion for any thinking man.
15:13The intangible had become tangible.
15:18By the end of the 18th century,
15:20we didn't really understand what temperature was.
15:24But we did have a means of measuring it.
15:27As for light, the opposite was true.
15:30We understood what it was, but we couldn't measure it.
15:34However, the study of the other great form of energy,
15:37electricity, was in its infancy.
15:40For thousands of years, lightning and strange tales of torpedo rays
15:49were the only manifestations of this awesome force that we knew about.
15:58Striking fear into our hearts,
16:00all we could do was observe its blinding light and its searing heat.
16:04Before the 18th century, we had little idea what electricity was.
16:12We could only puzzle over the effects of static electricity,
16:15marvel at the destructive power of lightning.
16:18So how did we come to exploit and measure it so precisely?
16:29To answer that question, we have to go back 300 years
16:32to a world that was dark, cold and quiet.
16:36When the working day was determined by when the sun set,
16:38letters were delivered by horseback.
16:41Electricity was just a spectacle performed by showmen
16:43who called themselves electricians.
16:47But this was also a time when people were becoming
16:50increasingly inquisitive about their world.
16:54The 18th century was a remarkable period in the history of measurement.
16:59This was the age of the Enlightenment,
17:00when scientists were looking at the world around them with a keen eye,
17:04trying to find rational explanations for the phenomenon that they observed.
17:09And the strange force of electricity was coming under scrutiny.
17:13The breakthrough was made here in Pavia in northern Italy,
17:21and it was made by a charismatic and brilliant young scientist
17:24called Alessandro Volta,
17:26who became obsessed with the seemingly magical power of electricity.
17:30In a state of deep emotional distress,
17:33after a torrid love affair with a beautiful opera singer called Mariana,
17:36the lovesick Volta threw himself
17:38into the investigation of animal electricity.
17:41And the animal he studied was the torpedo ray,
17:47a fish capable of electrocuting its prey.
17:55What Volta was intrigued by was,
17:58what was it inside the torpedo ray that was causing this electrical shock?
18:02When he looked inside its anatomy,
18:04what he found was a column of cells that seemed to be responsible for the shock.
18:09So this is what he tried to copy.
18:12Now, Volta must have played around with many different ideas,
18:15trying things out, nothing worked,
18:17until suddenly he had a breakthrough.
18:19His lead came from the work of Luigi Galvani.
18:24Attaching copper and iron wires to a dead frog,
18:27Galvani discovered that he could make its legs twitch.
18:31He believed he'd found a strange new force inside the frog.
18:35Volta's brilliance was realising the phenomena was actually down
18:39to Galvani's use of two different metals.
18:42Inspired, he set about recreating the torpedo ray's cell column,
18:48using alternating types of metal.
18:54First of all, he took a copper metal plate,
18:57put that one down the bottom of the pile,
19:00and then on top of that,
19:01he put a metal plate made out of zinc.
19:03And then the next ingredient was a piece of card
19:08soaked in a weak acid solution.
19:11And then that gets put on top of the zinc.
19:15So that's our first cell.
19:17And then he's going to make copies of these cells,
19:20build up this kind of pile,
19:21a little bit like in the torpedo ray.
19:24Another piece of acid.
19:26So that goes on there.
19:29Now, to test his idea,
19:30what he did was to attach a wire
19:32to the bottom copper plate,
19:34another wire to the top zinc plate,
19:38and then what he hoped
19:39was he'd get an electrical shock
19:41if he joined these two together.
19:43And to really test it,
19:44what he did was to place the two ends of the wire
19:46on his tongue to actually feel the shock.
19:48So hopefully I haven't made this too powerful.
19:50Let's try this out.
19:54Yeah, it's quite gentle,
19:55but there is definitely the taste of a fizz of electricity.
19:59And the more cells I put on top of this,
20:01the bigger the current.
20:03Now, to prove that I'm not just acting,
20:04I've got a little light bulb here.
20:07So if I attach this to one end of the wire
20:09and then to the other,
20:12there we go.
20:14The light lights up.
20:17But what's amazing about this
20:18is it's not just a spark of static electricity
20:21or the shock of the ray.
20:24This is a gentle, continuous stream of electricity.
20:29This was the first time this had ever been done.
20:35And this is what really gave birth to the modern battery.
20:38In Voltar's typical self-confident and flamboyant way,
20:50he toured the lecture halls,
20:51showing off his great invention.
20:54Other scientists latched on to the discovery,
20:57using the cells in their own experiments.
20:59It would take hundreds of years
21:05before we fully understood electricity,
21:07but Voltar had begun to unlock its secrets.
21:13Electricity, light and heat
21:15were no longer supernatural forces,
21:18but tangible forms of energy
21:20that were attracting the greatest minds in science
21:23to their study.
21:23And these scientists soon realised
21:27better measurement would hold the key
21:30to harnessing their immense power.
21:36By the time Voltar was creating
21:38the world's first continuous electrical current,
21:42thermometers had already been around for 200 years.
21:45But readings varied depending on whose model you used.
21:51It took Polish-born scientist
21:53Daniel Fahrenheit
21:54to make the first big leap
21:56in standardising temperature measurement.
22:00He chose mercury
22:01as it expands more uniformly than other liquids,
22:05and is liquid over a wide temperature range.
22:09But his real innovation
22:10was to introduce two reliable
22:13and reproducible fixed temperature points,
22:16so a scale could be calibrated.
22:19At the low end,
22:21he chose the melting point of pure ice,
22:23at 32 degrees.
22:25And the upper end,
22:2796,
22:28the temperature of human blood.
22:31This later changed
22:32to the more practical boiling point of water,
22:35at 212.
22:37And as Celsius,
22:39simplified things,
22:40choosing a 100 degree scale
22:43based on the boiling and freezing points of water.
22:45His brilliance was to calibrate his thermometers
22:49to standard atmospheric pressure,
22:52making them accurate whatever the weather.
22:59Both scales are still used today,
23:02but it took the industrial revolution
23:04to show up their limitations.
23:06as the demands for ever greater accuracy and range grew,
23:12the Celsius and Fahrenheit thermometers
23:14were simply not up to the job
23:16in the fast-evolving world of heavy industry.
23:18by the end of the 19th century,
23:30steam engines like this watt engine
23:32were really driving the industrial revolution.
23:35They were pumping down mines in distilleries,
23:41controlling the machines in factories across the country.
23:45This extraordinary engine at Papelwick
23:48will be pumping over a million and a half gallons of water a day
23:52for the citizens of Nottingham.
23:53The six huge furnaces would use 100 tonnes of coal a week,
24:06shoveled by a team of 14 men
24:08working back-breaking shifts around the clock.
24:13The temperature inside this furnace
24:15is getting to over 1,000 degrees centigrade.
24:18That's heating water at the back,
24:20which turns into steam,
24:21which, using some valves,
24:22drives the pumps of the watt engine.
24:30Now, the thing is,
24:31when water turns into steam,
24:33the volume changes by a factor of 1,600,
24:36and that's where all the power comes from.
24:38Now, the pressure depends on the temperature
24:40inside this furnace.
24:42Get that temperature wrong,
24:43the whole place blows sky-high.
24:48By the second half of the 19th century,
24:51boilers were exploding
24:52at a rate of almost one every four days
24:55in America alone.
24:58One of the worst incidents
24:59was later called
25:01the Titanic of the Mississippi.
25:07The American Civil War had just finished,
25:10and the steamship Sultana,
25:12packed with newly released Union prisoners of war,
25:14was returning home.
25:15At 2 a.m. on April 27th, 1865,
25:22her boilers exploded,
25:25tearing the ship apart.
25:29Over 1,700 lost their lives
25:33in what remains
25:34one of America's worst maritime disasters.
25:37steam power was changing our world,
25:43but at a high cost.
25:45Thermometers simply wouldn't work
25:47at these high temperatures.
25:49The glass would break.
25:51And the Fahrenheit and Celsius scales themselves
25:54were far too inaccurate
25:55at recording temperatures,
25:57so much higher than the boiling
25:58and freezing points
26:00that they were based on.
26:01A new means of measuring
26:04high temperatures
26:05was urgently needed,
26:07and the answer ultimately came
26:10from an unlikely source,
26:12electricity.
26:14The breakthrough came in 1820,
26:17when a German scientist,
26:19Thomas Johann Seebeck,
26:21realised that if he took
26:22two wires of different metals
26:24and wound them round each other
26:25and put the two wires
26:27inside the furnace,
26:29then took a compass
26:32and put it over the wires,
26:36he discovered that
26:36the needle of the compass moved.
26:38There was a magnetic field
26:40being caused by this wire.
26:43The difference in temperature
26:44between the end inside the furnace
26:46and this end here
26:48is causing a difference
26:50in voltage potential,
26:51which is creating
26:52an electrical current
26:54running through this.
26:54the electrical current
26:55causes the magnetic field,
26:57and that's what's being picked up
26:58when I put the compass
27:00over the top of this.
27:02This simple observation
27:03is what led to the creation
27:05of a device called
27:06a thermocouple.
27:09In fact,
27:10a modern-day thermocouple
27:11can actually measure
27:13this voltage difference.
27:15I can record
27:16at the heart of the furnace
27:17that it's going up
27:18900 degrees.
27:20Look, it just topped
27:20over 1,000 there.
27:23For me,
27:24the amazing thing
27:24is that we're using
27:25the measurement
27:26of electricity
27:27to actually find out
27:29what the temperature
27:29is inside this furnace.
27:32But before we could
27:33fully harness heat's power,
27:35we needed to understand
27:37what heat really was.
27:42In the 18th century,
27:44a popular theory
27:45among scientists
27:46was that heat
27:47was an invisible liquid
27:48that flowed
27:49in hot substances.
27:55It took keen amateur scientist
27:57James Prescott Jewell
27:59in 1840
28:00to start to unlock
28:01its mysteries.
28:04And it begins
28:05at rather an unlikely place,
28:08a brewery.
28:08Rather fond of beer,
28:14Jewell realised
28:15that accurate temperature
28:16measurement
28:17was crucial
28:18to making a good pint
28:20in the family brewery.
28:21He became so good
28:23at measuring temperature
28:24that he claimed
28:25you could measure it
28:26to an accuracy
28:27of 1 200th of a degree
28:29Fahrenheit.
28:30But he also worked out
28:32something else,
28:33something that was crucial
28:34for scientists
28:35to understand.
28:36He devised
28:37a simple experiment
28:38that had
28:39an extraordinary result.
28:43Placing a paddle
28:45in a tank of water
28:46and turning it
28:47using the energy
28:48of a falling weight,
28:49he found that
28:50the temperature
28:51of the water
28:51went up.
28:53He also found
28:54that if the weight
28:55fell from even higher,
28:57the water
28:57got even warmer.
29:00Jewell had discovered
29:01mechanical energy
29:02could be transferred
29:04into heat.
29:08It was a huge breakthrough.
29:11Heat wasn't
29:12an invisible fluid,
29:13but a form of energy.
29:16But at the time,
29:18the scientific community
29:19largely shunned
29:20his findings,
29:22refusing to believe
29:23this middle-class brewer
29:25could have anything
29:26meaningful
29:26to contribute to science.
29:29It took a chance meeting
29:30for Jewell
29:31to be taken seriously.
29:33On honeymoon
29:34in the French Alps,
29:35and still obsessed
29:36with proving
29:37his theories on heat,
29:39Jewell spent his time
29:40not with his wife,
29:41but at waterfalls,
29:43measuring the difference
29:44in water temperature
29:45between the top
29:46and the bottom.
29:49And it was here
29:51that he bumped into
29:52the world-renowned scientist
29:53Lord Kelvin.
29:57Their friendship
29:58would revolutionise
30:00our understanding
30:01our understanding
30:01of heat.
30:03And inspired
30:04by the work of Jewell,
30:06Lord Kelvin set about
30:07devising a new
30:09temperature scale.
30:12No longer would
30:13temperature measurement
30:14be based on the boiling
30:15and freezing points
30:16of water,
30:17but on the very nature
30:19of heat itself,
30:21energy.
30:23Performing hundreds
30:24of gas experiments,
30:26Kelvin's goal
30:27was to find
30:27the coldest temperature
30:29in the universe
30:30and to use this
30:32as the base
30:33for his new scale.
30:34This is liquid helium
30:41and all this movement
30:43is caused by the molecules
30:44firing around inside it.
30:47But as the temperature
30:47drops,
30:49something strange
30:50starts to happen.
30:51The molecules
30:52slow right down
30:53until they virtually
30:54stop moving.
30:56The helium is close
30:57to a theoretical temperature
30:59called absolute zero.
31:02Kelvin calculated this
31:03to be minus 273 degrees Celsius,
31:08a temperature
31:08where molecules
31:10no longer move.
31:11There is no energy
31:13and therefore
31:14no heat.
31:16The inside of this flask
31:18is now one of the
31:19coldest places
31:20in the universe.
31:24Using absolute zero
31:25as the lower point
31:27of the scale,
31:28Kelvin had tied its base
31:29to the nature of heat.
31:32Yet to make
31:33the scale practical,
31:34what was needed
31:35was a fixed point
31:37higher up.
31:38Kelvin died
31:39before his theories
31:40were put into practice.
31:43But the scientist
31:44that followed
31:45in his footsteps
31:45chose a strange phenomena
31:47called the triple point,
31:50where a substance
31:51can exist simultaneously
31:53as a gas,
31:54liquid,
31:55and a solid.
31:56Now the reason
31:58measurement scientists
32:00like this triple point
32:01so much
32:01is that it happens
32:03at a very precise temperature.
32:06So at this point
32:07we see the nitrogen
32:09in liquid and gas form
32:11and we're going to reduce
32:14the pressure.
32:16As the pressure drops,
32:18so does the temperature
32:19and the nitrogen
32:21begins to solidify.
32:23And we should be able
32:24to get...
32:25There we go.
32:27We've now captured
32:28the nitrogen
32:29in both liquid,
32:31gaseous,
32:32and solid form.
32:33You can see this solid,
32:34kind of like nitrogen ice
32:36sitting on the top.
32:38And the gas is bubbling
32:39underneath,
32:39pushing the solid up
32:41and the liquid
32:41below that.
32:42The old Fahrenheit
32:45and Celsius scales
32:46were fixed to the boiling
32:48and freezing points
32:49of water,
32:50which can vary enormously.
32:52The beauty of triple points
32:53is that they never vary
32:55by more than
32:56a few millionths
32:57of a degree.
32:59Now with this idea
33:00of a theoretical
33:01absolute zero
33:02and these triple points
33:03corresponding to
33:04different substances,
33:05nitrogen,
33:06water,
33:07finally the world
33:08had a precise scale
33:10to measure temperature.
33:12Half a century
33:16after his death,
33:18the Kelvin was adopted
33:19as the international unit
33:21of temperature measurement
33:22and tied to a fixed point
33:25more accurate
33:26than Celsius and Fahrenheit
33:28could ever have imagined,
33:30the triple point of water.
33:33With it,
33:34incredible feats
33:35of engineering
33:36were now possible.
33:37From forging metals
33:39to growing crystals,
33:41the world finally had
33:42a temperature scale
33:44it could trust.
33:54Like heat,
33:56the story of electricity
33:57also took a giant leap forward
33:59during the Industrial Revolution.
34:03It was French maths prodigy
34:06and physicist André-Marie Ampère
34:08who was to make
34:09the next real breakthrough.
34:13Intrigued with Ersted's discoveries,
34:15he decided to further investigate
34:17the relationship
34:18between electricity
34:19and magnetism.
34:25Using apparatus
34:27very similar to this,
34:28he discovered
34:29that if he passed
34:29an electrical current
34:31between two parallel wires,
34:33it created a magnetic
34:34attraction between them.
34:36Now,
34:37I've beefed up the experiment
34:38a little bit
34:38by using these coils of wire,
34:41but if I turn on
34:41the electrical current,
34:42the coils
34:45are then attracted
34:47to each other.
34:48And the key thing for us
34:50is that
34:50the greater
34:51the electrical current,
34:52so if I beef that up a bit,
34:54the greater
34:56the magnetic force
34:58between them.
35:00Ampère had found
35:01a new way
35:03to measure electricity.
35:06By measuring
35:07the strength
35:08of the magnetic force,
35:09he was able
35:10to build a machine
35:11to measure current,
35:13called a galvanometer,
35:15named in honour
35:16of electrical pioneer
35:17Luigi Galvani.
35:21And there was
35:22a practical use
35:23to all this.
35:24Ampère's work
35:25was about to pave the way
35:27for modern communication.
35:32The first telegraph systems
35:34were basically a wire
35:35with a galvanometer
35:37stuck at each end.
35:41They worked
35:42by sending pulses
35:43of current
35:44down a wire,
35:45which then
35:46deflected these needles.
35:50Messages could now
35:51be sent
35:52at a speed
35:52of about
35:53six words a minute.
35:58But it took
35:59a grisly murder
36:00for this newfangled
36:01invention
36:02to be taken seriously.
36:03In 1845,
36:10John Towell
36:11poisoned his lover
36:12Sarah Hart
36:13with a deadly drink
36:14of prussic acid.
36:18Fleeing the scene,
36:20he jumped
36:20on a train
36:20to London.
36:23The alarm
36:24was raised
36:25and a telegraph message
36:26sent to Paddington Station.
36:28A murder
36:33has just been
36:34committed
36:34at Salt Hill
36:35and the suspected
36:36murderer
36:36was seen
36:37to take
36:37a first-class ticket
36:38to London
36:39by the train
36:40which left Slough
36:41at 7.42pm.
36:43He is in the garb
36:44of a Quaker.
36:48The message
36:49took ten minutes
36:50to get to London.
36:52The train
36:52took 50.
36:53On his arrival,
37:01Towell was met
37:02and tailed
37:02by a London bobby.
37:05News of his
37:05spectacular arrest
37:07made every paper
37:08in the country.
37:09The power
37:10of electrical
37:11communication
37:11was clear
37:12for all to see.
37:17Soon,
37:17telegraph lines
37:18were being laid
37:19across the world.
37:21A revolution
37:21in global communications
37:23was underway.
37:25But with no
37:26international system
37:27of measuring electricity,
37:29there were serious problems.
37:31If too much current
37:33was pushed down the line,
37:34the wires caught fire.
37:36Too little
37:36and the message
37:37never got through.
37:41With lots of competing
37:42and different units
37:43of electrical measurement
37:44in use,
37:46standardisation
37:46was urgently needed.
37:50And in 1881,
37:51on the site
37:52of the Grand Palais
37:53here in Paris,
37:55that dream
37:55would become
37:56a reality.
38:02It was at the first
38:03congress of electricians
38:05attended by 250 people
38:07from 28 different countries
38:08that the ampere,
38:10the volt,
38:10the ohm
38:11and the farad
38:12were finally defined.
38:14Ultimately,
38:15it would be the ampere
38:16that would become
38:17the international unit
38:18for electricity.
38:21Finally,
38:21the world had a standard
38:23for accurately measuring electricity.
38:25As the brains
38:27of the electrical world
38:28met behind closed doors,
38:30the French public
38:31were being treated
38:32to the greatest exhibition
38:33of electricity
38:34ever seen.
38:35All along the capital's
38:37tree-lined avenues
38:38and in the exhibition halls,
38:40the latest electrical lighting,
38:42trams,
38:42telephones,
38:43generating systems,
38:44signalling devices
38:45would have been gathered
38:46for the congress
38:47and the whole world
38:48to see.
38:49It must have been
38:49an extraordinary sight.
38:51In fact,
38:52onlookers described it
38:53as a great blaze
38:54of splendour.
38:56It really marked
38:57the spirit of the age,
38:58the spirit of innovation
38:59and invention.
39:00But it was a young
39:02American engineer
39:03and entrepreneur
39:04who stole the show
39:05that year.
39:08His name
39:09was Thomas Edison.
39:13In two enormous rooms
39:15filled with crystal chandeliers
39:17and hundreds upon
39:19hundreds of lights,
39:20the crowds were dazzled
39:21and amazed.
39:24But the invention
39:25that caught everyone's attention
39:27was his giant
39:28electrical generator,
39:30capable of lighting
39:311,200 lamps.
39:34With it were plans
39:36for the first complete
39:37electrical supply system,
39:40a system that would
39:41bring together
39:42the power of heat,
39:44electricity and light
39:45for the very first time.
39:48At its heart
39:49would be a steam-driven
39:51power station
39:52that would supply
39:53enough electricity
39:54to light over 100
39:56businesses
39:56and private houses.
39:57Edison was about
40:00to light up
40:01our world.
40:10Six months later,
40:11Edison's dream
40:12would become
40:13a reality.
40:13on the 4th of September
40:191882,
40:20Edison switched on
40:21his Pearl Street
40:22power station.
40:23An electrical current
40:24started flowing
40:25to 59 customers
40:26in Lower Manhattan,
40:28powering 400 lamps.
40:31The newspapers reported
40:33how, in a twinkling,
40:35the area bounded
40:35by Spruce, Wall,
40:37Nassau and Pearl Streets
40:38was in a glow.
40:40It marked the dawn
40:43of the electrical age.
40:46And the world
40:47would never be
40:48quite the same again.
40:49Electricity
40:50had arrived.
40:55And even Edison
40:57must have been surprised
40:58by its popularity.
40:59Within two years,
41:14demand for Pearl Street
41:15electricity
41:16had rocketed tenfold.
41:18Electricity soon became
41:19a household commodity,
41:20like buying a load
41:21of coal
41:22or a box of matches,
41:23at least
41:23if you could afford it.
41:25The next great challenge
41:26was measuring
41:27how much people
41:28were using.
41:30But the galvanometer
41:31and the units
41:32defined in Paris
41:33couldn't do this.
41:36Edison could have
41:37charged his customers
41:38based on the number
41:39of lamps they had.
41:41But soon he realised
41:42this was not
41:43a profitable way
41:44to do business.
41:47What he needed
41:48was a way to measure
41:49current usage
41:50over time.
41:52And his solution
41:53was to use the principles
41:54of electroplating.
41:56Edison's first
42:00electricity meter
42:01basically consisted
42:02of a glass jar
42:04with two copper plates
42:06suspended
42:07in a copper sulfate solution.
42:10Now,
42:11as I pass electricity
42:12through the cell,
42:14then what happens
42:15is that atoms
42:16transfer from the solution
42:18onto the plate,
42:20making the plate
42:20heavier.
42:21now the key point here
42:25is that the total mass
42:27of copper deposited
42:29on the plate
42:29is directly proportional
42:31to the total current
42:33running through the system.
42:34So now if I switch off
42:35the electricity
42:36and we take the plate out,
42:38you can see here
42:40the copper
42:41that's been deposited.
42:43Now the amazing thing
42:43for me is that
42:44instead of measuring
42:45this rather elusive
42:46property of electricity,
42:47we're actually just
42:48measuring a change
42:49in weight.
42:50Finally,
42:51Edison had a way
42:52to charge his customers
42:53for the amount
42:53of electricity
42:54they'd used.
42:55He'd send out
42:56one of his employees
42:56to visit the cells,
42:59they'd take out
42:59the plates,
43:00measure the change
43:00in weight,
43:01and the customers
43:02would be billed
43:03accordingly.
43:03Now it wasn't
43:05a brilliant system
43:06but at least it was
43:07a system
43:07for measuring
43:08the amount
43:09of electricity
43:09that had been used.
43:16While the measurement
43:17of heat and electricity
43:18was making great advances
43:20in the industrial era,
43:22the quest to measure light
43:23had been all but forgotten.
43:26It took the emergence
43:27of street lights
43:28to change all this.
43:30before Edison
43:32lit up our world
43:33using electricity,
43:35the very first lamps
43:36were powered by gas.
43:41It was the beginning
43:42of the 19th century.
43:44Theft was on the rise
43:45and murder was commonplace.
43:48There was a desperate need
43:50for safer streets.
43:51and that came
43:54with the installation
43:55of the first public gaslights
43:57here in central London
43:58in 1807.
44:02Demand for this newfangled
44:04gaslighting soared
44:05and soon unscrupulous companies
44:07were cashing in
44:08selling low quality gas
44:10at high quality prices.
44:13The outrage that ensued
44:14forced the government
44:15to introduce a new measure
44:17for light intensity.
44:20It was called candle power
44:21and it was based
44:22on the brightness
44:23of a special candle
44:24made out of beeswax
44:26and the naturally occurring oil
44:28taken from the head
44:29of a sperm whale.
44:31The spermaceti candle.
44:37The new unit
44:38was to be the light
44:39produced by one spermaceti candle
44:42weighing one-sixth of a pound
44:44and burning at a rate
44:45of 120 grains per hour.
44:50It was the world's first attempt
44:52to try and produce
44:52a standard measure
44:54of light intensity
44:55but it was still very arbitrary.
44:57Light inspectors
44:58would go out
44:59hold up greasy pits of paper
45:00trying to compare
45:01the brightness of light
45:03coming from gas lamps
45:04to those of a candle.
45:06It had a fundamental problem
45:07that still haunts
45:08the measurement
45:09of light intensity
45:10to this day.
45:11It depends entirely
45:13on our own perception
45:14of light.
45:25Now this is the light
45:27produced by a hundred candles.
45:29In a moment
45:30I'm going to extinguish
45:3150 of them.
45:33The problem is
45:34that the pupil in my eye
45:36expands and contracts
45:37to control the amount
45:38of light entering them.
45:40Which means that
45:41when I extinguish
45:42half of them
45:42it isn't going to look
45:44half as bright.
45:58Now although the camera
46:00is recording
46:00a lower light condition
46:02to my human eye
46:04although I've got
46:05half as many candles
46:06this looks as bright
46:08as it did before.
46:14It took a remarkable
46:15series of experiments
46:17in the 1920s
46:18to solve the riddle
46:19of human light perception.
46:23In an international study
46:25200 people
46:26aged 18 to 60
46:28underwent a series
46:29of tests
46:30to find out
46:31what colour wavelengths
46:32we see best
46:33and how our eyes
46:34combine these different colours
46:36to perceive brightness.
46:38Their work would lead
46:40to the creation
46:40of the candela
46:42the unit we use
46:43to measure light today.
46:45Here at the National Physical Laboratory
46:52Dr Nigel Fox
46:54can show me
46:55how unreliable
46:56my eyes are
46:57as a means of measurement.
46:59Yes that's good.
47:00So let's measure.
47:02So it looks a bit like
47:03a 70s disco here.
47:06Yes.
47:07Yes.
47:07Well we can't quite
47:09reproduce the experiment
47:10of the 1920s.
47:12The equipment
47:12has all disappeared
47:13but what we try to do
47:15is to simulate
47:16the effect
47:16of that experiment here.
47:17So Marcus
47:18which of those lights
47:19looks the brightest to you?
47:25Well I would say
47:26that the green one
47:27seems to be a lot brighter
47:29than the red and the blue.
47:30The red and the blue
47:31maybe blue next
47:33and then the red third
47:34but yeah the green
47:35certainly seems the brightest.
47:36Well would it surprise you
47:38if I said the green
47:39is less than all of the others?
47:41Oh really?
47:41Less intense?
47:42That's right.
47:43Yeah you're not
47:43tricking me.
47:44No no no no this is
47:45So what's this recording then?
47:47This instrument is
47:48measuring the actual
47:48radiometric power
47:49that is coming from
47:50those different light sources.
47:53And as the instruments prove
47:54my eyes really are deceiving me.
47:58That's extraordinary.
47:59The red is actually
48:00much more powerful
48:02than the green
48:03yet my eye
48:03is seeing the green
48:05as more luminous.
48:06Exactly.
48:12The 1920s tests
48:14revealed not only
48:15that our eyes
48:16were much more sensitive
48:17to yellowish green light
48:18but that our age
48:20and sex
48:20also affect
48:21how we perceive
48:22the brightness of light.
48:26Compiling their results
48:27the scientists came up
48:29with an average human
48:30perception of brightness.
48:32It's roughly equivalent
48:33to how a woman
48:34in her late 20s
48:36sees light.
48:38To this day
48:40the definition of the candela
48:41remains locked
48:43to these findings.
48:46I can understand
48:47the need for the candela.
48:49I mean having a unit
48:50of measurement
48:51which measures
48:52how the human eye
48:53sees light
48:54is clearly useful.
48:55I mean take this traffic light
48:57that's coming up
48:57I want to know
48:58that it's bright enough
48:59that I'm going to see it
49:00but not so bright
49:01that it's going to dazzle me.
49:03The same applies
49:03to the car headlamps
49:05street lamps
49:06lights in our home
49:07but the list is endless.
49:15Because it's based
49:16on human perception
49:17there's something
49:18rather odd
49:19about the candela
49:20as a unit.
49:21I mean it's
49:21kind of the black sheep
49:23of the measurement family.
49:25And the candela's days
49:27are numbered.
49:29Today scientists
49:31are trying to base
49:32all measurement
49:32on the fundamental
49:34unchanging laws
49:35of the universe.
49:37We've done it
49:38for the metre
49:39basing it
49:40on the speed of light
49:41and the second
49:42on the movement
49:43of electrons
49:44inside an atom.
49:45Now the goal
49:49is to do the same
49:50for heat
49:50electricity
49:51and light.
50:02Today
50:03just as during
50:04the industrial revolution
50:05our ability
50:07to measure
50:08these energy units
50:09is failing
50:10to keep up
50:11with the demands
50:12of industry.
50:12Here at Rolls-Royce
50:19measuring and
50:20harnessing heat
50:21at temperatures
50:22higher than
50:222,000 degrees Kelvin
50:24will help deliver
50:25more fuel efficient
50:27and powerful
50:27jet engines.
50:29Accurately measuring
50:31very high temperatures
50:32is a huge
50:33technical challenge.
50:35This is the
50:36high pressure turbine
50:37blade.
50:38This is the first
50:39rotating component
50:40that the gas stream
50:42would encounter.
50:42coming down
50:43from the combustor.
50:44So whereabouts
50:45is that in here?
50:46So it's just
50:47downstream of the
50:48burns, yes.
50:49Right, so this
50:49is exposed
50:50to extreme temperatures.
50:51It is indeed
50:52and temperatures
50:53above its melting point.
50:54Above its melting point?
50:55Above its melting point.
50:56So this would actually
50:57should be melting then
50:58but okay
50:59so how do you
50:59make sure
51:00it doesn't melt?
51:00We actually have
51:01to heavily cool them
51:02so you can see
51:03some of the features
51:04that do that
51:04the holes
51:05on the surface
51:06there are passageways
51:08inside of the blade
51:09finished items
51:10would have a
51:11coating on them
51:12as well
51:13thermal barrier coating
51:14a ceramic layer
51:15which also takes
51:16a lot of the heat away.
51:18Despite state-of-the-art
51:19thermocouples
51:20computer modelling
51:21and thermal paints
51:22on the turbine blades
51:23the experts here
51:25can only achieve
51:26an accuracy
51:27of about 4 degrees Kelvin.
51:30Better accuracy
51:31isn't just
51:32a technical problem.
51:34The Kelvin scale
51:35itself loses accuracy
51:37the higher temperatures get.
51:38today new technologies
51:46are pushing temperature
51:47measurements
51:47to the absolute limit
51:49such that a new standard
51:50is critically needed.
51:52Here at the NPL heat lab
51:54they think they might be
51:55close to cracking it.
51:59Michael de Podesta
52:00has built the most
52:01accurate thermometer
52:02in the world
52:03an acoustic gas thermometer.
52:09It's the culmination
52:11of a 150-year story
52:13that began with Kelvin himself.
52:15What we're doing
52:16is we're determining
52:17temperatures
52:18in terms of the speed
52:20with which molecules
52:21are moving.
52:22What we measure
52:22is the speed of sound
52:24through argon gas
52:25trapped in this container
52:27down here.
52:28It seems extraordinary
52:29to be using sound
52:31in a way
52:31to be measuring temperature.
52:33Well, if you think
52:34about a sound wave
52:35momentarily
52:38gas is compressed
52:39and that heats up
52:41the gas
52:41and the gas
52:43then springs back
52:44and you're turning
52:45that thermal energy
52:46the motion
52:47of the microscopic motion
52:48of the molecules
52:49back into mechanical energy.
52:51So sound
52:52is directly linked
52:53to temperature.
52:55So what we measure
52:56is the speed of sound
52:58and what we can infer
52:59very, very directly
53:00is the speed
53:01of the molecule.
53:10If it's successful
53:11the acoustic gas thermometer
53:13will be as revolutionary
53:14for the measurement
53:15of heat
53:15as the atomic clock
53:16was to time.
53:18Just as Kelvin dreamt
53:19it will create
53:20an absolute system
53:22based on one
53:22of the fundamental
53:23constants of the universe
53:25the Boltzmann constant.
53:26A magical number
53:28which relates
53:28the movement of molecules
53:29to temperature.
53:31When that happens
53:33temperature
53:33will join the meter
53:35and the second
53:36in being tied
53:37to a universal constant
53:39of nature.
53:41And with it
53:42will come incredible precision
53:44with devices capable
53:47of measuring accurately
53:48at temperatures
53:49hotter
53:50than the surface
53:51of the sun.
53:54It will give us
53:56greater control
53:57of heat
53:57making engines
53:59more efficient
53:59and economical.
54:06Incredibly
54:06in a lab
54:07just down the corridor
54:08from the acoustic thermometer
54:10another breakthrough
54:11is underway.
54:12Here JT Janssen
54:21and his team
54:22are revolutionising
54:23the measurement
54:24of electricity
54:25and their work
54:28can be traced back
54:29to Volta's
54:30battery experiment.
54:34We now know
54:35if you break something
54:36down into its building blocks
54:37atoms
54:38you will find
54:40a positively charged
54:41nucleus
54:42orbited
54:43by negatively charged
54:44electrons.
54:46Metals like the copper
54:48and zinc
54:48used by Volta
54:49have electrons
54:51that readily detach
54:52from their nuclei.
54:53It is these loose
54:55moving electrons
54:56that enable
54:57electricity to flow
54:59forming a current.
55:02Using some of
55:03the strongest magnets
55:05on the planet
55:05and temperatures
55:07close to absolute zero
55:08JT's team
55:10are controlling
55:11the movement
55:11of single electrons
55:13and counting them
55:15as they pass through
55:16their experiment
55:17one at a time.
55:20We've been working
55:20on this experiment
55:21for about 10 years now.
55:23and it's all related
55:24to trying to
55:25redefine
55:27the ampere
55:28the unit for electrical
55:29current
55:29in terms of
55:30a fundamental constant
55:31of nature
55:32and in this case
55:33that's the charge
55:34of an individual electron
55:35and now we're at a level
55:37where we can control
55:39a billion electrons
55:40per second
55:40and we're only missing
55:41a few of those.
55:44JT's experiment
55:45will redefine
55:47our measure
55:47of electrical current
55:49using these
55:50individual electrons.
55:51they are fundamental
55:53particles
55:54the same
55:55throughout the universe.
55:57For scientists
55:58this is the goal
55:59tying measurement
56:01to the unchanging
56:02laws of physics.
56:07And their work
56:08won't just impact
56:09on the world
56:10of measurement.
56:11Controlling the flow
56:12of single electrons
56:13is key
56:14to developing
56:15quantum computers.
56:16this next generation
56:18of technology
56:19will produce computers
56:21capable of calculations
56:23that are vastly beyond
56:24what is currently possible.
56:26They could simulate
56:27the human brain.
56:31Model climate change
56:32in real time
56:32and data storage
56:34using electrons
56:35would mean
56:35virtually limitless capacity.
56:37as we delve deeper
56:43inside the fabric
56:44of our universe
56:45into the quantum world
56:47of subatomic particles
56:48measurement
56:50is undergoing
56:51a fundamental
56:52and exciting change.
56:56We are now using
56:57the very building blocks
56:59of matter
56:59to help us measure
57:01the world around us.
57:02even the black sheep
57:07of the measurement family
57:08the candela
57:09could soon be redefined
57:11tied to the flow
57:13of photons of light.
57:19What started
57:21with our senses
57:22and crude guesswork
57:23is now getting down
57:25to the smallest
57:26building blocks
57:27of the universe
57:27as our human urge
57:29for ever greater precision
57:31drives us forward.
57:32measurement
57:36has changed
57:37the course
57:38of science
57:38and civilisation.
57:41Now
57:42as the quantum age
57:43approaches
57:43our world
57:45is set to change
57:46once more.
57:52But this is all
57:53part of a story
57:54which started
57:55thousands of years ago
57:56when our ancestors
57:58began to measure
57:59time, length
58:00and weight.
58:02they were trying
58:03to understand
58:03the environment
58:04around them
58:05to measure it
58:06and ultimately
58:06to manipulate it.
58:10But isn't that
58:11really what's still
58:11driving us today?
58:13Because measurement
58:14is the key
58:15to understanding
58:16our place
58:17in the universe.
58:18our world
58:32is the hein
58:32that thearry
58:33is the tower
58:33of the universe
58:33to overcome
58:34and we're goingì‹œì£
58:35for a long time
58:36there.
58:36We'll have to check
58:36some more
58:37things about and
58:38we've got if you're
58:38going to keep it
58:39and they're not
58:39information
58:39for us.
58:40And look for you
58:41as We're going to have
58:41is the economy
58:41to improve the universe
58:42to achieve that
58:43how you do well
58:43itam
58:45and try to celebrate it
58:46and work with you already
58:47Amen.
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