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All human cultures build up a lot
of the stories they tell each other,

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their rituals, their religions, and
their science by thinking about light.

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Man of God declared light divine.

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Scientists bent it
through glass to see to the

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depth of space and the
minute interiors of cells.

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It seemed, by understanding
the truth about light,

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we would understand the
truth about everything.

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But it turned out, and
this is surely one the great

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paradoxes of the light stories
that we have been telling,

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it turned out, that the more
people can manipulate light,

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the more puzzling and tricky,
light turned out to be.

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And in very same idea that light
and truth go together, it turns

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out that a great deal of what
light gives us is an illusion.

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In 1664, the great
natural philosopher, Isaac

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Newton, performed his
ground breaking experiment,

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showing that a prism can split
white light into colored rays.

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But above all, what Newton
did with his prism was

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to set up a great challenge
for future generations,

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He'd shown white light
as a mixture of colors,

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but beyond that, he admitted
to be completely mystified.

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Color was light's last mystery.

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Understanding color would be
the key that would unlock the

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truth about light, and as it
did, it would change everything.

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Science, art, and even our
understanding of the human mind.

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The first step in the story
into the heart of light

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needed one of the greatest
upheavals in history.

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The industrial revolution
began in the late

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18th century textile mills
of North West England.

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People were forced to think about light and
particularly, color in a new and urgent way.

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Controlling color counted.
Because the British market was

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being flooded by brightly colored
clothes from India, from Asia.

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British industrialists
counted this flood with their

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own crafts and their own
industrially manufactured dyes.

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Standardizing those colors, getting

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chemical control over
how they were made, and

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then making sure they mix tightly with the
dye clothes, was the key to market success.

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Perhaps the most dramatic impact
of the new color industries was the

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way it changed folk sense, of what
was natural, what was artificial.

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Colors which were previously been
understood as matching natural objects,

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the blue of the sky, the green
of grass, the red of the rose,

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could be made completely artificially.

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Artificial dyes revealed
that many people didn't

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see a colored clothes the
same way as others did.

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For the first time, people realized there
was a mystery about the way we see color.

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It is inevitable that the puzzle of getting
color judgments systematically wrong,

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appears precisely at the place and the
time of mass color industrialization,

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North West England at the
end of the 18th century.

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The man who matters was John Dalton.

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John Dalton, the gifted son of
an impoverished weaver, threw

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himself into the new chemistry
of the industrial revolution.

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He is best known now for proposing
the atomic theory of matter,

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but his first scientific paper
was based on his realization

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that there was something awry
with his own color perception.

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Dalton, who was a Quaker,
showed several signs

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of getting color wrong
or judging it badly

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when he went to Quaker
meetings, he would sometimes

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turned up dressed in the
most inappropriately bright

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colors in a red gown,
not the sort of thing that

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a dweller, solid, Quaker
citizen should be wearing.

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For the first time in
history, Dalton started

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to systematically analyze
his own sense of color.

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He went back to nature and to his
childhood fascination with botany.

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The bright pink flower of
clover seemed bright blue to him.

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The pink geranium,
the pelargonium seemed

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absolutely blue when
he collected it outside.

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And when he brought it into the
house and looked it by candlelight,

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it changed strangely from
being blue to being yellow.

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Dalton meditated on this problem,

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was it special to him? Dalton,
who worked as a school teacher,

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asked his pupils whether
they had the same problem.

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And it turned out in a
class of about 2 dozen, 4

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or 5 boys suffered from
exactly the same puzzle.

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Dalton was the first person to identify
and scientifically study color blindness.

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Dalton himself thought it was caused
by a physical property of the eye,

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he came up with a gruesome
way of testing this idea,

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In Dalton's will, he
instructed his medical adviser,

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Ransom, to take out one of
his eyes, and dissect it.

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Because Dalton guessed that
the reason for his color

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blindness was that there was
a blue liquid inside his eye.

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Ransom followed Dalton's
will to the letter.

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He extracted one of the great
man's eyeballs and cut it open.

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There was no blue liquid.

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Ransom, instead,
described the eyeball as

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pellucid, it let the
light through perfectly,

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it showed no staining, no color,

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there was no blue liquid
inside, that couldn't be

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the explanation of Dalton's
own color blindness,

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instead, and this was
what was really suggestive,

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the problem must be to do
with some kind of judgments,

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something more psychological, something
between the brain and the back of the eye.

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Dalton may have got the cause
of color blindness wrong,

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but he proved that
condition ran in families£¬

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and it came in just a few common forms.

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He published this revolutionary findings
in the new industrial age's greatest city.

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Dalton's great lecture
of October 1794 on the

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Manchester literary and
philosophical society

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set a stage for nothing less than a

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revolution in the science
of light and color.

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The commercial imperatives of the
industrial revolution would lead

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to the discovery that the mind has
a role to play in how we see color.

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The booming factories and
towns of 18th century Europe,

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urgently needed brighter and
more efficient lamps and lanterns.

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Designing them would revolutionize our
understanding of the true nature of light.

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Now put the lens in. The key
figure in this story was an

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American immigrant living in
Europe called Benjamin Thompson.

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Thompson did one of the most intriguing
experiments ever on the behavior of light,

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but it started because he was trying to save
money for his employers, the city of Munich.

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The Munich government gave him
a really important job which was

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to clean every single beggar off
the Munich streets and put them

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into newly designed workhouse
which Benjamin Thompson constructed.

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As a reward, Thompson
became a Count, Count Rumford

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Now on of the things his workhouse
is going to need was lighting,

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and so Rumford decided to do a series
of extraordinarily precise experiments

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to work out what the cheapest
kind of lighting could possibly be.

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One set of experiment he was really keen
on doing was seeing if it is possible

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to compare say, the brightness of a
candle, with the brightness of sunlight,

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now he need to stop down the
sunlight that was coming into his lab,

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so what he did was to
use a series of colored

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filters in order to
bring the light down.

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But as he put colored filters
in front of sunlight or lamps,

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he noticed something
absolutely extraordinary.

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So, look at the shadow through
this red filter, and you

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see that the shadow is now
a rather beautiful turquoise,

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and the shadow cast by this lamp,
which was black, has gone red.

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Well, we might be able to see why
the shadow on the left has gone red,

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because we have put red filter in front
the light that is illuminating that shadow,

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but what is going on with the other
color, that was Rumford's big problem.

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At this point, Rumford
tried to eliminate from his

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field of view, everything
except the turquoise shadow,

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he decided to look at the
turquoise shadow through a tube

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painted black on the inside.
And this was even spookier.

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To Rumford's utter amazement,
when he used his tube, so

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the only thing in his field
of view was the blue shadow,

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its blueness disappeared.

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I was not able even to
tell when the colored

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glass was before the
lamp and when it was not,

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and though the assistant often exclaimed the
striking brilliancy of the shadow's color,

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I could not discern in it the least
appearance of any color at all.

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He couldn't see any color change,
whatever the assistant was doing.

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He saw a uniform shadow.

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That was really hard to understand.

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Two people see the
same thing differently.

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There could only be one
explanation, that color exhibited by

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one of the shadows only is real,
that of the other is imaginary,

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being an optical deception
occasioned in someway unknown to us.

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These colors that we see are
actually the work of our own brains,

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they are not simply just
out there in the world.

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Rumford had shown, for reasons
he didn't understand, that the

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human mind can add colors to the
dull colorless grey of a shadow.

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Rumford himself hoped that the
effect of this discovery on the

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future of art, and painting would
be revolutionary and so it was.

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Contemporary painters, like Joseph
Turner, realized that colored shadows

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would make their paintings more
authentic, more psychologically real.

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This is The Fighting Temeraire. The
shadowed side of the tug boat, instead of

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being grey, is tinged with violet to bring
out the melancholy mood of the sunset.

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The shadows in Claude Monet's paintings
of Rouen Cathedral are alive with color,

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yellow to evoke the haze of mid day sun,

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purple for the dying light of twilight.

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Rumford recon that the implications
of the fact that colors are

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partly made up by the mind would
then go far beyond painting.

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Rumford, kind of had a dream,

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if colors are subjective,
then you ought to be able to

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use them to entertain people,
to seduce people in fact.

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The idea was that you
could key the keyboard of a

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harpsichord to colored lights,
and when you played a note,

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a color would appear.

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Rumford called this device,
an optical harpsichord.

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He never actually built one, it was
too difficult with 18th technology.

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It took 200 years for Rumford's
dream of light and music to come true.

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But back in the late 1700, people
were observing more and more

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aspects of light and color which
they had no way of explaining.

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What it caused to John
Dalton's color blindness?

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What was causing
Rumford's colored shadows?

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What was needed was a breakthrough
in the understanding of what light is.

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And that breakthrough came in the
early 1800, but not from someone who

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was investigating light, but from
someone who was investigating sound.

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The hero of this story was
a wealthy, and precocious

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Cambridge medical student
called Thomas Young.

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Now as a member of the college
and a wealthy one of that

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Thomas Young liked horse riding, he
liked music, and he liked placing bets.

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And there is a bet recorded
in the gambling book

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of the college that
Thomas Young, as a student,

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bet that before he graduated, he would
write the best essay ever on sound.

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He thought he did, no one
else did, and he lost the bet.

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But that essay argued that
if you listen hard to organ

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pipes, you are unlocking the
mystery of the way sound travels

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An amazing truth about light would be
hidden in Young's essay about sound.

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His initial interest was
to investigate a fact that

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people had known since
antiquity: sound travels in waves.

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For instance, columns of air in
organ pipes vibrate up and down,

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rather like ripples of water
going back and forth in a lake.

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Young studied the unusual and distinctive
way in which sound waves behave,

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particularly when they overlap.

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You play a single not on the
organ, and it sounds pure.

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if you add another note,
which is out of tune,

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you begin to hear beats,

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which are relates to the difference
in frequency between the two notes.

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When two waves meet,
they can either add or

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subtract, you get pulses
of addition and difference.

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Young now made a dramatic
leap in imagination,

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he realized that light must work
in the same way that sound does.

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If you shine a beam of light
through a card with two slits in it,

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as the two light beams
emerging from the slits

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recombine, you see a patter
of bright and dark bands.

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The two beams of light cancel each other

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out in places just as
the two sound waves do.

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That could only mean one thing:
light, like sound, was a wave.

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Today, everything from
optical fibers to spectacle

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design is based on the
idea that light is a wave.

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But at the time, it was an incredible
idea, from Newton on, the existing

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notion of light was that it is a stream
of tiny core parcels, or particles.

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Young's radical idea was
greeted with house of derision.

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Young's lectures on his new theory that

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light travel in waves
were very controversial.

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It was going right against 150 years
of models of light as a particle.

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Young hit back.

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And the example that
came to mind was a pond.

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Think of waves traveling on the surface of a
pond, and you could see the way light moves.

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Young's lecture with
their watery model of light

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were a powerful argument
for a new wave theory

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which would explain how we
see and how light travels.

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The idea that light was
a wave is now heralded

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as one of the great
discoveries of science.

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It meant color was at
last comprehensible.

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Just as different frequencies of
sounds gives you different notes,

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different frequencies of light
give you different colors.

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00:22:31,188 --> 00:22:33,967
On essence, the idea was really simple

228
00:22:33,991 --> 00:22:37,294
and it was illustrated during the 19th

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00:22:37,295 --> 00:22:41,379
century by pretty simples
machines like this.

230
00:22:45,589 --> 00:22:49,512
Now imagine that this is a wave of light

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00:22:49,569 --> 00:22:57,972
what Young asked is what happens when
light waves of this kind enter our eyes.

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00:22:58,602 --> 00:23:05,104
It seemed obvious to him that what
the retina is doing is vibrating,

233
00:23:05,159 --> 00:23:09,414
it is not some kind of passive
screen that get hit by particles,

234
00:23:09,544 --> 00:23:12,560
it is a vibrating membrane,

235
00:23:12,595 --> 00:23:17,300
and the faster it vibrates
explains the difference in colors,

236
00:23:17,677 --> 00:23:23,402
so the blue making rays
are vibrating really fast,

237
00:23:23,682 --> 00:23:26,494
red rays much more slowly.

238
00:23:28,437 --> 00:23:35,720
And Young even guessed something really
important about the way we sense color,

239
00:23:36,195 --> 00:23:42,892
if light is a wave, and colors are
different frequencies of that wave,

240
00:23:43,513 --> 00:23:47,832
then maybe in the very back
of the eye, we have different

241
00:23:47,833 --> 00:23:52,374
kinds of senses which pick up
different kinds of vibrations.

242
00:23:53,230 --> 00:23:59,447
Young experimented with spinning color
wheels, and he saw if you spun fast enough,

243
00:23:59,451 --> 00:24:06,660
just three colors: red green and
blue, can combine to appear as white.

244
00:24:08,456 --> 00:24:11,783
What Thomas Young
concluded from this is that

245
00:24:11,784 --> 00:24:15,327
the vast panoply of colors
humans think they see

246
00:24:15,486 --> 00:24:23,716
comes from combining our responses to just
3 frequencies of light, red green and blue.

247
00:24:25,939 --> 00:24:31,730
Now if that model is right, this
will begin to explain the kinds

248
00:24:31,731 --> 00:24:37,343
of color blindness that his
friend John Dalton was exhibiting,

249
00:24:37,643 --> 00:24:41,477
because if one set of receptors
wasn't working properly,

250
00:24:41,704 --> 00:24:45,869
you wouldn't pick up that kind
of color, that was Young's idea.

251
00:24:46,425 --> 00:24:51,253
Dalton, the man who begun
the study of color perception,

252
00:24:51,254 --> 00:24:56,166
provided bizarre posthumous
confirmation of Young's idea.

253
00:24:56,266 --> 00:25:01,320
In 1995, 150 years after his death,

254
00:25:01,537 --> 00:25:05,454
doctors extracted DNA
from Dalton's eyeball,

255
00:25:05,561 --> 00:25:10,659
which amazingly have been preserved
by a Manchester scientific society,

256
00:25:10,873 --> 00:25:16,051
Dalton's DNA showed that he
was blind to red and green.

257
00:25:19,850 --> 00:25:23,919
Back in the 19th century,
understanding the mystery of

258
00:25:23,920 --> 00:25:27,915
how we see color couldn't
have come on a better time,

259
00:25:28,015 --> 00:25:31,804
color perception was now
a matter of life and death.

260
00:25:56,749 --> 00:26:01,979
In 1875, in Sweden, near the town
of Largarenda, a train missed a

261
00:26:01,980 --> 00:26:07,288
red signal, and hurtle towards
another in the middle of the night.

262
00:26:07,723 --> 00:26:11,186
9 people died, hundreds were injured.

263
00:26:13,206 --> 00:26:17,196
A local professor, guy called Holmgren,

264
00:26:17,608 --> 00:26:20,451
guessed that one of
the guys on the north

265
00:26:20,452 --> 00:26:23,564
bound train was probably
color blind and then

266
00:26:23,925 --> 00:26:30,408
mistaken a red light for green and sent
the train hurtling to its destruction.

267
00:26:35,422 --> 00:26:39,073
In Britain where there
were more railway lines than

268
00:26:39,074 --> 00:26:42,654
anywhere else, the government
lurched into action.

269
00:26:44,524 --> 00:26:49,837
Experts from the scientific establishment
were hired to do tests on whether

270
00:26:49,838 --> 00:26:55,359
there were good ways of spotting the
color blind among its drivers and pilots.

271
00:27:01,581 --> 00:27:05,251
The leader of the inquiry
was Lord Rayleigh, a

272
00:27:05,252 --> 00:27:09,000
very well connected and
very wealthy gentleman.

273
00:27:09,733 --> 00:27:12,694
Rayleigh was an expert
on light and sound

274
00:27:12,769 --> 00:27:15,545
and he had already
studied the rather bizarre

275
00:27:15,546 --> 00:27:17,958
fact that a lot of his brothers in law,

276
00:27:18,107 --> 00:27:21,845
including the eminent Tory
politician, Arthur Balfour,

277
00:27:22,114 --> 00:27:25,991
seems to suffer from a
strange form of color blindness

278
00:27:25,992 --> 00:27:29,445
in which they were over
sensitive to red lights,

279
00:27:29,523 --> 00:27:33,218
not as you would have thought
a normal problems among Tories.

280
00:27:33,407 --> 00:27:37,530
But what Rayleigh then did
was to introduce a system of

281
00:27:37,531 --> 00:27:41,654
absolutely rigorous color
testing on the working class.

282
00:27:44,941 --> 00:27:49,697
Building on Young's 3 color theory,
Rayleigh devised the first ever color

283
00:27:49,698 --> 00:27:54,195
blindness tests for every train
driver and boat pilot in the country,

284
00:27:54,721 --> 00:27:58,268
and by the early 1900,
the modern color perception

285
00:27:58,269 --> 00:28:01,676
tests which most people
now take were developed.

286
00:28:07,821 --> 00:28:13,178
But back in Victorian times, the
human ability to discriminate between

287
00:28:13,179 --> 00:28:18,384
subtle differences in color was at
the heart of massive controversy.

288
00:28:20,748 --> 00:28:24,911
It was widely accepted
that all people, not just

289
00:28:24,912 --> 00:28:28,905
the color blind, see
color slightly different,

290
00:28:29,041 --> 00:28:35,369
and some Victorian scientists believed
that if they could accurately measure this

291
00:28:35,370 --> 00:28:42,006
variation, they would prove, categorically,
the most repugnant of all European ideas:

292
00:28:42,098 --> 00:28:43,344
white supremacy.

293
00:28:45,127 --> 00:28:49,351
Color perception played
an absolutely crucial

294
00:28:49,352 --> 00:28:53,943
role in European ideas
about human nature itself,

295
00:28:54,891 --> 00:29:03,631
the coming fashion for racist explanations
of the difference between human groups

296
00:29:03,982 --> 00:29:10,938
cashed out its ideas in the area of
differential sensitivity to colors.

297
00:29:12,824 --> 00:29:14,114
This is how it worked,

298
00:29:14,373 --> 00:29:21,114
it was believed that animals had
faster, better attuned senses than humans

299
00:29:22,134 --> 00:29:26,649
and at that time, it was also
believed that black people were

300
00:29:26,650 --> 00:29:31,018
lower down in the evolutionary
scale, so more like animals.

301
00:29:31,468 --> 00:29:34,987
And to prove that fact,
all you had to show was

302
00:29:34,988 --> 00:29:38,872
that their responses to
light and color were better.

303
00:29:40,305 --> 00:29:46,138
In 1898, a group of Cambridge based
scientists and medics went from

304
00:29:46,139 --> 00:29:52,743
England to the Torres Straits, the
islands between Australia and new guinea.

305
00:29:52,868 --> 00:29:58,115
One of the most important members of this
expedition was a man named William Rivers.

306
00:29:58,743 --> 00:30:01,115
Rivers was an extraordinary figure.

307
00:30:01,322 --> 00:30:05,362
He was a brilliant
physiologist, and medic.

308
00:30:05,426 --> 00:30:11,350
He'd written the definitive accounts of
optics, and vision, and color perception.

309
00:30:11,557 --> 00:30:16,122
What Rivers was gonna do was to set
up a psychology lab on the beach.

310
00:30:18,009 --> 00:30:21,778
This is one of the actual
bits of equipment Rivers took

311
00:30:21,779 --> 00:30:25,749
to the Torres Straits to assess
native's color perception.

312
00:30:26,440 --> 00:30:29,812
It is called a tintometer,
it was designed to

313
00:30:29,813 --> 00:30:33,551
test human sensitivity to
subtle changes in color.

314
00:30:34,213 --> 00:30:42,970
What Rivers was going to do was to test
how Torres Straits islanders matched colors,

315
00:30:43,320 --> 00:30:47,309
so for example, he might
take a particular red,

316
00:30:47,537 --> 00:30:51,442
and dropped it in to this tube,

317
00:30:51,501 --> 00:30:55,817
and then invite the
islanders to select a glass

318
00:30:55,818 --> 00:30:59,864
color which corresponded
to that, like that,

319
00:31:02,224 --> 00:31:06,672
then the islander would look down
the tube, and degree that this two

320
00:31:06,673 --> 00:31:11,572
colors are the same, or this shall be
slightly darker, or slightly lighter.

321
00:31:12,160 --> 00:31:16,093
What this allowed Rivers
to do, then, was to

322
00:31:16,094 --> 00:31:20,288
construct numerical color
scales for islanders'

323
00:31:20,289 --> 00:31:24,396
color perception and
test whether islanders or

324
00:31:24,397 --> 00:31:28,503
others could make finer
color discriminations.

325
00:31:31,451 --> 00:31:36,306
Day after day, bemused islanders
queued up to look at tinted

326
00:31:36,307 --> 00:31:41,321
slides, spinning disks, and have
their reaction time measured.

327
00:31:53,542 --> 00:31:57,812
But River was in for big
surprise, what he found,

328
00:31:57,813 --> 00:32:02,168
by an large, the range of
discrimination of colors

329
00:32:02,385 --> 00:32:07,076
he found amongst the islanders
was not bit different from

330
00:32:07,077 --> 00:32:11,848
the range of discrimination
of colors amongst the English.

331
00:32:13,064 --> 00:32:17,245
In other words, the
English differs from each

332
00:32:17,246 --> 00:32:21,244
other as much in their
color discrimination

333
00:32:21,245 --> 00:32:25,516
as they did on average
for many Torres Straits

334
00:32:25,517 --> 00:32:29,424
islander. The psychic
unity of human kind,

335
00:32:29,674 --> 00:32:34,185
most people see things
in roughly the same way.

336
00:32:37,154 --> 00:32:41,302
To Rivers it turned no credit,
when he found that this evidence

337
00:32:41,303 --> 00:32:45,191
contradicted his original
hypothesis, he simply ditched it.

338
00:32:50,525 --> 00:32:56,815
On his return to England, Rivers spear
headed a movement that argued that there

339
00:32:56,816 --> 00:32:59,488
was no scientific evidence for the

340
00:32:59,489 --> 00:33:03,340
superiority of European
culture over any other.

341
00:33:06,994 --> 00:33:11,358
For many of the sides I think
Rivers is an extraordinary hero,

342
00:33:11,638 --> 00:33:18,638
He understood extremely well that European
culture, Cambridge culture could be

343
00:33:18,639 --> 00:33:25,993
studied in exactly the way that other
cultures was studied by European scientists.

344
00:33:26,241 --> 00:33:28,710
He has a wonderful story about what it

345
00:33:28,711 --> 00:33:31,763
would be like if an
islander from the Pacific

346
00:33:31,992 --> 00:33:37,124
came to Cambridge and began
to study the Cambridge natives,

347
00:33:37,414 --> 00:33:39,021
surely Rivers pointed out,

348
00:33:39,220 --> 00:33:44,222
this islander would naturally
assume that the natives of Cambridge

349
00:33:44,223 --> 00:33:49,523
had some kind of primitive, or
sentimental, or superstitious mentality

350
00:33:49,721 --> 00:33:54,432
which completely explained their
bizarre rituals and strange behavior.

351
00:33:56,534 --> 00:34:01,276
Studying the human response to
light created two new sciences:

352
00:34:01,637 --> 00:34:04,255
psychology and anthropology,

353
00:34:07,893 --> 00:34:10,955
but light itself remained enigmatic.

354
00:34:11,169 --> 00:34:14,881
Thomas Young's idea of
light waves was accepted,

355
00:34:14,916 --> 00:34:17,428
but what was these waves made of?

356
00:34:17,687 --> 00:34:20,770
The answer would come
from studying an aspect

357
00:34:20,771 --> 00:34:23,584
of light, but it is
not at first obvious,

358
00:34:23,632 --> 00:34:28,922
the fact that the light doesn't just
show us the world, it changes it.

359
00:34:34,189 --> 00:34:37,547
As anyone who had a rather
bad sunburn would tell you,

360
00:34:37,634 --> 00:34:41,776
light doesn't leave the
body it touches unaffected,

361
00:34:41,797 --> 00:34:44,445
on the contrary, light is a powerful

362
00:34:44,446 --> 00:34:47,902
chemical, physiological,
and biological agent

363
00:34:47,952 --> 00:34:53,206
which can have the most huge effects
on anything with which it interacts.

364
00:35:01,173 --> 00:35:05,507
The story of this discovery of
the most miraculous of light's

365
00:35:05,508 --> 00:35:09,562
properties begins in the late
1700s in industrial England

366
00:35:09,769 --> 00:35:13,697
with one of the greatest
English chemist Joseph Priestley.

367
00:35:18,322 --> 00:35:23,906
Joseph Priestley, a Yorkshire
man, of impeccable intellectual

368
00:35:23,907 --> 00:35:29,671
credentials, tough minded,
radical, materialist, and ambitious,

369
00:35:29,688 --> 00:35:34,330
was one of the leading natural
philosophers of late 18th century Britain.

370
00:35:34,559 --> 00:35:40,401
And for Priestley and his closest
friends, light and life went together.

371
00:35:40,711 --> 00:35:48,061
In this experiment, Priestley put
a mouse into a sealed bell jar,

372
00:35:48,131 --> 00:35:53,831
to test what happened to the air,
as the mouse breath in and out

373
00:35:53,866 --> 00:36:01,551
Fairly quick, the mouse
sickened, got exhausted, and died.

374
00:36:02,111 --> 00:36:06,998
This air, he reckoned, must
be really bad, really bad

375
00:36:06,999 --> 00:36:11,795
not just for living animals,
but for plants as well.

376
00:36:11,842 --> 00:36:18,424
So into the jar, Priestley
introduced a set of growing plants.

377
00:36:18,447 --> 00:36:22,536
And he left them there
for several weeks.

378
00:36:23,208 --> 00:36:27,257
To his amazement, they grew happily.

379
00:36:27,941 --> 00:36:35,534
Whatever was in the air that killed the
mouse seemed to make plants flourish.

380
00:36:38,784 --> 00:36:45,593
Priestley decided to test what
it was in the air where the mouse

381
00:36:45,594 --> 00:36:52,506
had died that was responsible for
encouraging the life of plants.

382
00:36:52,523 --> 00:36:55,568
He would simply introduce another mouse.

383
00:36:56,981 --> 00:37:00,248
The result was absolutely amazing,

384
00:37:00,278 --> 00:37:03,998
he found, provided that
the plants was growing

385
00:37:03,999 --> 00:37:07,638
there, that the animal
would suddenly revive.

386
00:37:07,938 --> 00:37:13,507
This was, what he called, the luxury
air, which only a couple of mice

387
00:37:13,508 --> 00:37:18,917
and myself have had the privilege
of breathing, and there was more,

388
00:37:19,155 --> 00:37:25,968
what Priestley found was that the quality
of the air wasn't just improved by growing

389
00:37:25,969 --> 00:37:32,861
the plant in it, if you shone a light on
the plant, the air quality went shooting up.

390
00:37:32,883 --> 00:37:38,118
What it showed was that light
shining on the green matter

391
00:37:38,119 --> 00:37:43,353
in plants could restore the
air to an almost paradisiacal

392
00:37:43,354 --> 00:37:48,498
quality where it would keep
animals alive for unparallel

393
00:37:48,499 --> 00:37:54,455
periods of time, where flames
would burn with extraordinary life.

394
00:37:54,601 --> 00:37:59,083
Light and life went together.

395
00:37:59,497 --> 00:38:04,588
We now know Priestley's
discovery as photosynthesis,

396
00:38:05,038 --> 00:38:09,472
the remarkable way plants
absorb the energy from light,

397
00:38:09,473 --> 00:38:13,906
and in the process, convert
carbon dioxide into oxygen.

398
00:38:14,762 --> 00:38:18,192
Light doesn't just show
us the world, it is a

399
00:38:18,193 --> 00:38:21,697
form of energy that is
essential for all life.

400
00:38:25,466 --> 00:38:29,332
The discovery that light
was energy and could effect

401
00:38:29,333 --> 00:38:33,489
powerful chemical changes
would have surprising results.

402
00:38:33,581 --> 00:38:37,931
It would open up a world that
no one had ever seen before.

403
00:38:47,597 --> 00:38:51,308
The story begins with
Tom Wedgwood, son of the

404
00:38:51,309 --> 00:38:55,176
famous potter Josiah.
Tom Wedgwood's experiments

405
00:38:55,177 --> 00:38:58,887
would kick start one of
the most revolutionary

406
00:38:58,888 --> 00:39:01,966
technologies of all time, photography.

407
00:39:04,830 --> 00:39:08,284
It began with Tom try to
help out the family business.

408
00:39:08,624 --> 00:39:13,487
Wedgwood's pots were famous
for their hand drawn decorations

409
00:39:13,488 --> 00:39:18,509
and tom wanted to find a way of
decorating pots automatically.

410
00:39:21,476 --> 00:39:26,821
So what Wedgwood did was to
prepare of special chemical

411
00:39:26,822 --> 00:39:31,785
mixture, made up of silver
nitrate and common salt.

412
00:39:32,104 --> 00:39:37,939
Others have noticed that silver nitrate
goes black when light shines on it.

413
00:39:38,004 --> 00:39:41,661
But Wedgwood experiment
it with ways of using

414
00:39:41,662 --> 00:39:45,557
this to draw patterns
what he called sun prints.

415
00:39:47,700 --> 00:39:54,607
What I am going to do is to make
a sun prints by wrapping my silver

416
00:39:54,608 --> 00:40:02,429
nitrate with this foil and then exposing
it suddenly to a very bright light.

417
00:40:04,693 --> 00:40:10,448
What we get are these
blackened images where

418
00:40:10,449 --> 00:40:16,331
the silver nitrate has
been hit by the light.

419
00:40:17,333 --> 00:40:21,572
Deluged as we are by
fantastic photographic images,

420
00:40:21,573 --> 00:40:25,484
these grey splodges
looked rather unimpressive,

421
00:40:25,580 --> 00:40:31,001
But in 1770, they gave a
glimpse of a wonderful future.

422
00:40:32,383 --> 00:40:35,740
Wedgwood and his
collaborators were absolutely

423
00:40:35,741 --> 00:40:38,882
fascinated by this
process of sun printing.

424
00:40:38,892 --> 00:40:42,983
Because what is meant was
that there might be a way of

425
00:40:42,984 --> 00:40:47,893
preserving forever the information
that light carries to the eye.

426
00:40:47,928 --> 00:40:55,325
The dream of enlightenment immortality was
turning into the reality of photography.

427
00:40:55,926 --> 00:41:01,375
Within 50 years of Wedgwood's
experiments, paper soaked in silver

428
00:41:01,376 --> 00:41:07,568
nitrate was being used to capture real
images. Photography became a craze.

429
00:41:07,584 --> 00:41:11,569
The expose is going to have
to be about 30 seconds. OK.

430
00:41:11,618 --> 00:41:15,968
Stand probably with your
head or your shoulders so

431
00:41:15,969 --> 00:41:20,659
that they can supported by
the mantelpiece behind you.

432
00:41:20,721 --> 00:41:23,355
Now this could make you
bit of uncomfortable,

433
00:41:23,356 --> 00:41:25,474
could you draw yourself up a little.

434
00:41:26,237 --> 00:41:29,562
Photography pandered to
the vanity of middle class

435
00:41:29,563 --> 00:41:33,605
Europeans, cause having your
own portrait was now affordable.

436
00:41:36,502 --> 00:41:40,551
Photography was a very
seductive and popular art,

437
00:41:40,552 --> 00:41:45,005
but I think it was also seen
as extremely threatening.

438
00:41:45,396 --> 00:41:48,556
All sorts of social
boundaries were broken

439
00:41:48,557 --> 00:41:52,156
down or breached by the
new photography process.

440
00:41:52,632 --> 00:41:56,491
Things you weren't supposed to
see, places you weren't supposed

441
00:41:56,492 --> 00:41:59,989
to look at, images that were
not for popular consumption,

442
00:42:00,289 --> 00:42:06,277
the boundaries between elite
tastes and vulgar industrial tastes,

443
00:42:06,545 --> 00:42:13,093
all these fences were being torn down
by the chemical process of photography.

444
00:42:14,001 --> 00:42:17,279
29... 30. Thank you very much.

445
00:42:23,535 --> 00:42:27,148
Photography was crucial
to Florence Nightingale

446
00:42:27,149 --> 00:42:30,234
campaigns to improve military hospitals,

447
00:42:30,293 --> 00:42:33,617
it helped fund the salvation
army, and it brought home

448
00:42:33,618 --> 00:42:36,820
to the public the horrors
of the American civil war.

449
00:42:41,714 --> 00:42:47,085
But photography will do more
than uncovering social secrets,

450
00:42:47,122 --> 00:42:53,456
the ability to capture light would reveal
unimagined truth about the natural world.

451
00:42:53,619 --> 00:42:57,446
It would revolutionize
biology, engineering, and

452
00:42:57,447 --> 00:43:01,977
ultimately through physics,
take us into a new dimension.

453
00:43:08,860 --> 00:43:14,997
It started with a simple question,
what happens when a horse gallops?

454
00:43:16,333 --> 00:43:20,497
In the age of the horse,
it was an old question

455
00:43:20,498 --> 00:43:24,488
as how exactly they
move when they galloping.

456
00:43:24,526 --> 00:43:28,912
Do their feet, all,
simultaneously, come off the ground?

457
00:43:28,963 --> 00:43:33,655
Now that was an ancient question, but
you couldn't solve it with the naked eye

458
00:43:36,341 --> 00:43:40,612
Eadweard Muybridge, a photographer
on the west coast of America,

459
00:43:40,729 --> 00:43:44,360
was commissioned for a
bet, to use this new fangled

460
00:43:44,361 --> 00:43:48,830
technology to prove once and for
all, how a horse really moved.

461
00:43:50,056 --> 00:43:54,033
Muybridge's plan was to use
24 cameras placed in a row

462
00:43:54,034 --> 00:43:57,865
across the race track, each
attached to a trip wire.

463
00:43:58,145 --> 00:44:00,804
And when the horse
galloped past, its exact

464
00:44:00,805 --> 00:44:03,885
movement at that instant
will be caught on camera.

465
00:44:13,758 --> 00:44:17,907
Muybridge then developed
the photos and had a

466
00:44:17,908 --> 00:44:22,508
series of amazing images
of horses moving quickly.

467
00:44:25,084 --> 00:44:30,989
It was true that at one point in the gallop,
the horse takes all its fee off the ground.

468
00:44:31,024 --> 00:44:34,612
Something you could never
see with the naked eye

469
00:44:34,613 --> 00:44:38,566
which the camera had now
revealed for the first time.

470
00:44:39,578 --> 00:44:45,906
But the ability to freeze motion with a
photograph was far more than a gimmick,

471
00:44:45,981 --> 00:44:50,349
others believed that if they
could examine animal motion in fine

472
00:44:50,350 --> 00:44:54,717
enough detail, they would be able
to replicate it, artificially.

473
00:44:55,192 --> 00:45:01,150
A French scientist, Etienne Marey,
had a particularly audacious dream

474
00:45:01,542 --> 00:45:06,943
Using Muybridge's cameras, he hoped
to discover the secrets of flight.

475
00:45:17,517 --> 00:45:23,847
But it turned out pretty quickly that
birds are just too quick and move in far too

476
00:45:23,848 --> 00:45:27,356
complicated way to be
able to be photographed

477
00:45:27,357 --> 00:45:30,635
the way Muybridge took
pictures of horses.

478
00:45:31,397 --> 00:45:36,532
So Murey cast about for another
kind of camera, and he found one.

479
00:45:36,567 --> 00:45:40,993
A camera that worked like
a gun, when you fire it,

480
00:45:40,994 --> 00:45:45,246
it took an enormous number
of shots each second,

481
00:45:45,404 --> 00:45:52,321
so what Murey would do would be to
point this gun at a bird and follow it

482
00:45:52,322 --> 00:45:59,705
through the sky taking first hundreds
and then thousands of shots each second.

483
00:46:08,855 --> 00:46:13,862
The scientific study of bird
motion now became possible.

484
00:46:17,635 --> 00:46:25,085
And by the end of the century, Murey's
photographs, not just of flying birds,

485
00:46:25,086 --> 00:46:32,535
but also of how winds controlled and
are effected by the air flow around them

486
00:46:32,574 --> 00:46:38,369
were being used to design the very
first effective flying machine.

487
00:46:41,302 --> 00:46:46,446
Photography not only revealed
what you couldn't see with

488
00:46:46,447 --> 00:46:51,320
the naked eye, it let humans
reveal their own dreams.

489
00:46:51,815 --> 00:46:55,121
Murey's bird photos
directly inspired the

490
00:46:55,122 --> 00:46:58,899
Wright brothers who built
the first aeroplanes.

491
00:46:59,006 --> 00:47:05,164
And his camera was adapted into the first
movie camera by the Lumiere brothers,

492
00:47:12,163 --> 00:47:16,748
By 1900, in this world of
new technological wonders,

493
00:47:16,749 --> 00:47:22,198
scientists finally believed they
could explain what light was.

494
00:47:22,413 --> 00:47:28,289
Building on Thomas Young's idea that
light is a wave, the great Scottish

495
00:47:28,290 --> 00:47:33,844
scientist James Clerk Maxwell showed
what this mysterious wave were.

496
00:47:36,201 --> 00:47:46,573
Pulses of electromagnetic energy. Humanity's
long quest to understand light seemed over.

497
00:47:48,927 --> 00:47:53,094
Light, it was argued, was
completely understood, we know what

498
00:47:53,095 --> 00:47:57,529
it is, we know where it came from,
and we know where it is going,

499
00:47:57,932 --> 00:48:02,171
light is a form of
electromagnetic radiation which

500
00:48:02,172 --> 00:48:06,825
travels through empty space
at a finite measured speed,

501
00:48:06,873 --> 00:48:11,873
and the physics of light, the technology
of light became a kind of symbol

502
00:48:11,874 --> 00:48:17,008
of the great successes of physics and
engineering and the whole of science.

503
00:48:18,357 --> 00:48:22,050
But there was a dramatic
twist in the tale,

504
00:48:22,289 --> 00:48:27,472
enter a Swiss patent clerk,
called Albert Einstein,

505
00:48:27,517 --> 00:48:33,920
aged just 25, using the idea that light
was an energy wave, Einstein was forced

506
00:48:33,921 --> 00:48:40,003
to conclude that all the laws of physics
needed to be completely rewritten.

507
00:48:44,640 --> 00:48:49,299
To understand how Einstein
could think so differently from

508
00:48:49,300 --> 00:48:53,801
his predecessors, picture
the world in which he grew up.

509
00:48:53,992 --> 00:48:58,247
So imagine you were
living in an European city

510
00:48:58,248 --> 00:49:02,593
around 1900, your world
had completely changed,

511
00:49:02,653 --> 00:49:06,223
you saw people whizzing
past on bicycles, the first

512
00:49:06,224 --> 00:49:10,343
horseless carriages, motorcars,
you could go to the cinema,

513
00:49:10,473 --> 00:49:14,830
and see exact reproductions
of what it is like

514
00:49:14,831 --> 00:49:19,373
to move really fast
through space, through time.

515
00:49:19,977 --> 00:49:24,723
Einstein¡¯s was the first
generation went to the cinema. And

516
00:49:24,724 --> 00:49:29,935
like most people, he loved watching
how time could be played with,

517
00:49:32,645 --> 00:49:38,582
speed it up, slow down, and even frozen.

518
00:49:38,653 --> 00:49:43,712
Einstein began to realize that time
might variable in the real world

519
00:49:43,713 --> 00:49:48,917
too, and you'd experience it if you
could travel like a beam of light.

520
00:49:50,949 --> 00:49:54,969
And he certainly began to
imagine what it would be

521
00:49:54,970 --> 00:49:59,226
like sitting on a light
beam traveling through space,

522
00:49:59,897 --> 00:50:04,926
all sorts of paradoxical effects,
he quickly worked out would follow,

523
00:50:05,328 --> 00:50:09,543
Flying along a light beam into
the depth of space, Einstein

524
00:50:09,544 --> 00:50:13,757
would see a reality completely
different to the normal one.

525
00:50:14,510 --> 00:50:19,088
Time would stop, distance stretch out,

526
00:50:19,460 --> 00:50:22,696
it was just as weird as a cinema trick.

527
00:50:24,769 --> 00:50:30,455
And 1915, he published on his
general theory of relativity,

528
00:50:30,477 --> 00:50:36,084
an astonishing intellectual
achievement, it declared that humanity's

529
00:50:36,085 --> 00:50:41,772
most basic intuitions about space,
time, and light cannot be trusted.

530
00:50:46,574 --> 00:50:50,177
Now Einstein's big
idea was that when light

531
00:50:50,178 --> 00:50:54,435
travels near a heavy object,
like our sun, it bends

532
00:50:58,084 --> 00:51:06,194
What the gravitation of a very heavy
object does is to distort space and time.

533
00:51:06,472 --> 00:51:12,604
Near very heavy objects,
straight lines curve.

534
00:51:14,945 --> 00:51:19,083
Put in another way, a
vast entity like a star

535
00:51:19,084 --> 00:51:22,952
makes empty space,
the void itself, curve,

536
00:51:25,467 --> 00:51:30,038
it seemed bizarre, but if
Einstein's incredible idea

537
00:51:30,039 --> 00:51:34,782
was right, it could be proved
by looking at the stars.

538
00:51:36,227 --> 00:51:41,804
Near the sun, light will
change direction, it will curve,

539
00:51:41,805 --> 00:51:47,766
and the apparent position of
stars beyond the sun will shift.

540
00:51:48,345 --> 00:51:53,745
We will be able to see stars in
positions that weren't there before.

541
00:51:54,766 --> 00:51:58,307
But normally the sun
is so bright; that it

542
00:51:58,308 --> 00:52:02,506
blanks out the stars that
is in the sky behind it,

543
00:52:03,315 --> 00:52:07,914
there is only one rare
occasion, when we can see the

544
00:52:07,915 --> 00:52:12,946
stars behind the sun, and
that is during a total eclipse.

545
00:52:21,066 --> 00:52:25,879
During an eclipse, the sun's
disk is completely darkened,

546
00:52:25,880 --> 00:52:31,107
the temperature drops, and the
sky seems to be extremely dark.

547
00:52:31,286 --> 00:52:35,451
Some of the stars, which the
sun's light otherwise is too bright

548
00:52:35,452 --> 00:52:39,295
for us to see, some of those
stars suddenly become visible,

549
00:52:39,395 --> 00:52:46,698
What you want to do, is take a photo of a
star you can see just past the sun's edge,

550
00:52:46,966 --> 00:52:49,514
and that would mean,
that the light wave from

551
00:52:49,515 --> 00:52:52,006
that star is coming
really close to the sun.

552
00:52:52,285 --> 00:52:56,542
If Einstein is right, then
that light ray will bend a bit,

553
00:52:56,789 --> 00:52:59,850
and the star will seem
to have shifted from

554
00:52:59,851 --> 00:53:03,190
where it normally is
when the sun is not there.

555
00:53:04,015 --> 00:53:08,911
Einstein worked really,
really hard, to trying get

556
00:53:08,912 --> 00:53:13,806
astronomers to watch stars
during a solar eclipse,

557
00:53:14,199 --> 00:53:17,784
because if those stars
seemed to shift position

558
00:53:17,785 --> 00:53:21,145
a bit, then his theory
will be proved right.

559
00:53:32,081 --> 00:53:36,517
In 1919, there was a total
solar eclipse, and a team of

560
00:53:36,518 --> 00:53:41,032
the finest British astronomers,
led by Arthur Eddington,

561
00:53:41,322 --> 00:53:47,089
armed with best telescopes and
photographic equipments went to Africa and

562
00:53:47,090 --> 00:53:53,090
Brazil to prove whether Einstein's mad
ideas about space and time were true.

563
00:53:54,050 --> 00:53:59,142
The scientific world held its
breath and waited for the result.

564
00:53:59,463 --> 00:54:04,359
It took months to do all the
comparisons and calculations, but at

565
00:54:04,360 --> 00:54:09,255
a meeting of the prestigious royal
astronomical society in London

566
00:54:09,605 --> 00:54:16,131
in November 1919, Eddington and his
colleagues were able to stand up and

567
00:54:16,132 --> 00:54:22,747
say: our photographic data proves,
unambiguously, that Einstein is right.

568
00:54:22,813 --> 00:54:28,004
A small shift of stars had
completely changed the world.

569
00:54:29,551 --> 00:54:33,952
All of a sudden, literately
overnight, Einstein became

570
00:54:33,953 --> 00:54:37,952
a world celebrity. The
new Newton, a global hero,

571
00:54:38,041 --> 00:54:43,185
there were cartoons of the
whole of earth with a single flag

572
00:54:43,186 --> 00:54:48,244
attached to the planet, saying
simply: Einstein lived here.

573
00:54:52,593 --> 00:54:56,262
He became not just a
celebrity, but kind of figure,

574
00:54:56,531 --> 00:55:00,809
of what it was to be a scientist,
what it was to be a genius,

575
00:55:00,810 --> 00:55:04,880
and I guess what it is to
obscene the secrets of universe.

576
00:55:05,179 --> 00:55:08,024
one person who visited
Einstein said visiting

577
00:55:08,025 --> 00:55:10,559
Einstein is like visiting 4th dimension.

578
00:55:11,014 --> 00:55:14,683
He stopped being a human being,
he became a force of nature.

579
00:55:16,621 --> 00:55:22,335
And the drama with which this
revolutionary discovery was proclaimed

580
00:55:22,336 --> 00:55:27,967
put the new science of light right
at the center of the news media,

581
00:55:28,056 --> 00:55:33,347
it made the physics of
light into a global event.

582
00:55:35,883 --> 00:55:42,028
But above all, what Einstein had done was
overturn 3000 years of thinking about light.

583
00:55:42,306 --> 00:55:47,686
Every philosopher, from the
ancient Greeks to 9th century Arabs,

584
00:55:47,986 --> 00:55:54,705
from medieval monks to Isaac
Newton, from Galileo to Maxwell,

585
00:55:55,015 --> 00:56:01,757
had unquestioningly accepted one fact
about light: it travels in straight lines,

586
00:56:01,951 --> 00:56:07,126
And now Einstein had shown
that even this was wrong.

587
00:56:11,877 --> 00:56:19,260
So Einstein was right, light don't travel
in perfect geometrical straight lines,

588
00:56:19,347 --> 00:56:25,156
but it travels through a
space and time that is curved.

589
00:56:25,244 --> 00:56:30,296
that makes light as it were depart
from the straight and narrow.

590
00:56:31,739 --> 00:56:35,800
Light had once be the
sign of reliability.

591
00:56:36,069 --> 00:56:38,627
It had been a tool for astronomers;

592
00:56:38,969 --> 00:56:44,071
it had been their basic technique
for finding out how the cosmos worked.

593
00:56:44,762 --> 00:56:51,101
Now it turned out, that far from
being a tool, light was a puzzle,

594
00:56:51,102 --> 00:56:56,967
it was a problem, it twisted,
it turned, it bend, it strayed.

595
00:56:57,309 --> 00:57:05,377
Einstein's world became a world in
which light needed to be teased upon,

596
00:57:06,048 --> 00:57:10,597
and in which the message that
light brought from the most

597
00:57:10,598 --> 00:57:15,695
distant stars was a puzzle, and
a challenge to human intellects.