so one of the things that I love about science is sometimes the work of two
different people
end up coming together and building a massively important oevre of scientific
knowledge
Such as the story a light and polarization especially with one man
Augustine Jean Fresnel, or in American English
Fresnel
So Fresnel was a French engineer. He wasn't this PhD-I'm-going-to-study-physics-and
figure-out-how-the-world-works kinda dude he was just really really really
interested in Light. Between the years 1814 1816 he had pissed off the French
government
While he was in exile he decided
Alright, I'm just gonna can play around with light, because it's fun!
So he starts playing with light, and comes up with these mathematical equations.
So he's got all this math, and gets back to Paris and he shows it to some people and they're like
You just described with Christiaan Huygens proposed a hundred and forty years ago
Supported by Thomas Young but no one had actually unified it yet. And Fresnel
Goes
Who? I guess its French so it's: Qui? Fresnel had no idea who Christiaan Huygens
was and no idea who Thomas Young was and yet he comes up with all this math that
supports the wave theory of light and in fact had reproduced Thomas Young's
double slit experiment
without ever knowing it! Anyway now that propels on the light scene he pairs up
with Dominique Francoise Jean
Arago, who had in 1809 discover the polarization in the sky, and in 1811
invented the first polariscope for analyzing polarization of crystals and
minerals.
In 1816, Fresnel and Arago show that two polarized beams of light,
if they're at the end ninety degrees polarization to each other, will never interact
meanwhile back over in
England Thomas Young starts thinking about this and looking at calcite, and
makes a really big leap, in 1817,
when he proposes that in order for light to work as a polarized ray
there has to be at least one part of it that that is a transverse wave in a
longitudinal wave, which is what sound is a cycle moves along with the direction
of motion, but with the transverse wave the cycles cut across the direction of
movement
Oh Yeah....
This is a big leap by Thomas Young to say that light had a transverse component 'cause
up until then
all they really knew about was longitudinal waves: sound waves, water waves
these are all on longitudinal waves and that's what they'd found in nature. A lot of the
particle theorists were like: now you're just talking crazy talk! And they still
wouldn't believe it until something really important happens once again with our
friend Fresnel!
In 1818 the Academy des Sciences de Paris decided that the next year's Grand
Jury Prize will be awarded you whoever could solve the question
of diffraction. One of its members Simeon Denis Poisson believed that one of the
people who believed in particles would be the one to prove that particles explain
diffraction and therefore light could not be a wave.
But, Fresnel! Fresnel publishes his Memoirs on
Defreaction, which contains most of the equations for the wave-like nature
light and submits it to the Academy des Sciences de Paris
And they look at it and they're like: well, this is pretty cool; and Poisson looks it over
and goes
Oh, Hang on a minute! If this is true, if I shine a light
added disc, I should see a dot in the middle (of the shadow)
So if you can show me that then yeah, we'll believe you... believing that it would
never happen.
Arago goes out, and does the experiment and
The dot's there! Which is now ironically called the Poisson point
So since Arago essentially proves Fresnel's equations to be a hundred
percent
right, the Academy des Sciences awards the Grand Jury Prize to Fresnel for his
Equations on diffraction
And they become the standard equations that was still used today.
This 1819 Grand Jury Prize settled all the critics
of the wave theory of light. Poisson and a lot of the other corpuscle theorists
of light finally start saying.. well...maybe we were...
uh.. well, we were wrong... we were just weren't quite right
But Fresnel had one more important thing to give. In 1821 he publishes a
very important paper based on his observations of the polarization light.
Basically he calculated mathematically and show that if light had
any longitudinal component it could not be polarized - it had to be a 100 percent
transverse wave. And this is why today we still look at the wave component of
light
as being a transverse wave. So, thanks Fresnel! You're really cool!
And that's ignoring all your other stuff that you did which we don't have time to
get into today
Don't forget to subscribe to Tech Laboratories because next time I'm gonna
be cutting my
own prism out of calcite. I thought "Hey, this should be easy" it turns out it's not
but it's really cool! 'Till next time, I'm Tech Adams saying "Keep thinking"
and thanks for watching.
Invented in 1811 by Dominic Francois Jean Argo
Not Argo - that's a movie, Arago. In 1816 Fresnel and Arg....
Arago
Great movie by the way! At the moment the cat
is playing with my wired remote and I actually think its quite adorable.
You're ruining the shot!