- When we think of astronomy,
we tend to think of something like this,
a person studying the position
of the stars with a telescope,
but from the mid-1800s to the mid-1900s,
it looked more like this,
studying the image of different frequencies of stars
from a photograph made with an image from a telescope
and through a diffraction grating or a prism.
And now of course we use computers not photographs,
but the basic idea of studying the intensity
of different frequencies of light,
visible or invisible called spectroscopy
is a backbone of astronomy.
But what does that have to do with Joseph Fraunhofer
who was a glass maker not an astronomer?
How did a glass maker
discover spectroscopy and the diffraction grating?
Well, it's a crazy story.
Want to hear it?
Ready? Let's go.
(upbeat music)
I'd like to start in Munich, Bavaria
on a Tuesday July 21st, 1801.
I picked that momentous day
because that was when Joseph Fraunhofer was 14 years old
and he and his boss's wife were buried
in a collapsed building for several hours.
Now, you might think that was a terrible event
for young Joseph, and I'm sure it was very traumatic,
but it ended up being the event
that changed his life for the better.
Admittedly, his life up to that point
had been pretty horrific.
He was the youngest of 11 children
born to a poor overworked glass maker
in the small town of Straubing, Bavaria.
Seven of his older brothers and sisters died in childhood
from poverty, sickness, and dangerous work conditions.
On top of that, his mother died
when he was just 10 years old
and his father died the year afterwards
probably poisoned from the toxic fumes from the glasswork.
Orphaned and nearly alone, he was indentured
for six years to a decorative glass maker
named Phillip Weichelsberger in far-away Munich.
Before his parents died, Fraunhofer rarely went to school
because his father needed the help
in the glass making industry
and after his parents' death it was even harder.
There was a holiday school
that would teach workers to read and write
on Sundays and late at night.
But Weichelsberger wouldn't let Fraunhofer go.
Even at 14, Joseph Fraunhofer could barely read.
Then, as I said before, in 1801
the building that he was in collapsed
and he and his master's wife were buried alive.
Soon, a large group of volunteers came to rescue them
including the Prince of Bavaria
came by regularly to encourage the diggers.
Mind you at the time Munich was a pretty small town,
population around 40,000.
After four hours of digging,
they found young Fraunhofer saved by a cross-beam
whereas his master's wife
whose name has been lost to time and sexism
was crushed to death.
Fraunhofer's escape was the talk of the town
and the prince decided that the child
was a gift of providence
and personally gave the young boy money
and asked his privy councilor, Joseph Utzschneider,
to look out for him from then on.
Fraunhofer used the money to get out of his indentureship
and started engraving business that went bust
less than six months later.
Soon poor Fraunhofer found himself
back working for Weichelsberger and miserable.
Meanwhile, in 1804, the privy councilor, Utzschneider,
left politics and started a mechanical institute
with a friend,
and in 1806, Utzschneider took pity on Fraunhofer
and hired him as an assistant to the institute
where he impressed everyone.
At about the same time,
Utzschneider hired a glassmaker named Pierre Guinand
to make quality lenses for their telescopes.
Within a year, Guinand asked for a large raise
and Utzschneider agreed,
but with the stipulation
that Guinand had to teach all of his secrets
to 20-year-old Fraunhofer.
This partnership did not last long.
Fraunhofer and Guinand guess just didn't get along.
And by 1809, Utzschneider decided that his protege
was the far superior glassmaker
and actually paid Guinand to just go away
and not make glass anymore
and promoted Fraunhofer at just 22 years old
to be the director of the glassworks
and a junior partner of the Optical Institute
of Utzschneider, Reichenbach and Fraunhofer.
By 1811, Fraunhofer had 48 employees,
and by 1820, he was made the director of the institute.
Meanwhile, Fraunhofer was constantly searching
for ways to improve the quality and precision of his glass.
That is why in 1814 or so,
27-year-old Fraunhofer started looking for a way
to find single colors
so he could study precisely how much they refracted or bent
when they went through glass
or as he put it,
"It would be most advantageous if one could measure
for every kind of glass the dispersion for every color;
but the different colors in the spectrums
have no definite limit."
Fraunhofer had noticed a bright yellow-red spot from a lamp
when he viewed it through a prism
and decided to see if the sunlight had the same bright mark
that was diffracted in the same way.
He therefore shined sunlight
through a small opening to get a beam
and then through one of his prisms
and examined the light on the screen.
However, instead a bright spot at the yellow-red,
instead he saw dark lines.
Shocked, he looked through the light through a telescope
and as he put it,
"I saw with the telescope an almost countless number
of strong and weak vertical lines."
Now, Fraunhofer wasn't the first one person
to see shadows in the sunlight.
12 years before in 1802,
an English scientist named William Hyde Wollaston
spent a long time determining the refractive index
of different materials by using a prism.
In this paper, Wollaston noticed five dark lines
and two fade lines in sunlight,
but he only thought they were bands
distinguishing four colors of red, yellowish,
green, blue, and violet.
Unlike Wollaston however,
Fraunhofer with the aid of his telescope
realized that the lines had nothing to do with the color
remarking, "The strongest lines do not in any way
mark the limit of various colors.
There's almost always the same color
in both sides of a line,
and the passage from one color into another
cannot be noted."
Fraunhofer labeled the thicker lines with capital letters
and counted over 540 lines in a ridiculously detailed chart.
And his labels are still used today.
Fraunhofer wondered if these dark lines
were inherent in the sunlight
or if there were some trick of the experiment
from like the shape or the size of the opening.
So after several experiments
he came upon the idea of looking at the spectrum from Venus
as he could examine it without making the light
pass through a small opening.
He then found, "the same lines
as those which appear in sunlight,"
with the caveat that some of the lines were hard to see
with the dim light from Venus.
He then turned his telescope to study some of the stars
and found to his surprise that they weren't all the same.
For example, the star Sirius had, "three broad bands
which appear to have no connection with those of sunlight,"
and various stars, "seem to differ among themselves."
Thus it seemed pretty conclusive
that these dark bands had something to do with the sunlight
or the starlight itself
and therefore could tell you something
about the sun or the stars,
or as he put it, he was
"convinced that these lines and bands
are due to the nature of sunlight."
He then went back to his lamplight and studied it again
now with a prism and a telescope,
and found that the reddish-yellow
bright line in the spectrum
consists of two very fine bright lines
which in intensity and distance apart
are like the two dark lines D.
Fraunhofer didn't know that the bright lines
from his lamp were from burning sodium
and the dark lines in the sunlight
were from the sodium on the atmosphere of the sun
absorbing those same frequencies.
Now, Fraunhofer was very busy
and didn't publish anything significant again
for seven more years till 1823.
When he had been experimenting with thin beams of light,
he noticed that before he added the prism,
the image of his beam of light on the screen
had colored edges.
Fraunhofer was intrigued by the colored lights at the edges
as it reminded him of the rainbow of light
you could get from a prism
and decided to investigate further.
He therefore started with light
going through a small opening
that he could change with a screw
and observed the results on a screen with a telescope.
He found there are many dim rainbows
on the side of the central beam of diminishing intensity.
He also found the position of this mini-rainbow
was a constant divided by the width of the opening.
This by the way is why single slit diffraction
is often called Fraunhofer single slit diffraction.
Fraunhofer became irritated
by how difficult his experiment was to do
because with light going through a tiny slit,
the image he was looking at was so very dim.
He therefore had the idea
of using multiple slits in a row or a grating.
He then had an ingenious idea of how to make a grating.
He round thick wire between two screws.
There were only slightly wider than the wire.
So he ended up with 260 parallel wires
that were 20 milli-inches thick
and only 3.8 milli-inches apart.
When he conducted the experiment,
instead of looking like a single slit only brighter,
he found a whole new result, writing,
"I was most surprised to observe
the phenomena seen through the telescope
when the grating was used was entirely different
from those observed by diffraction
through a single opening."
He then found that the first peak looked,
"exactly like those seen through a good prism,"
and even recreated his Fraunhofer lines with his grating.
Joseph Fraunhofer was appointed a Royal Professor
and knighted in 1824.
Tragically, less than three years
after publishing his work on gratings,
he felt ill from working with glass with heavy metals in it,
the same thing that killed his father
and died when he was just 39 years old.
At his funeral, his former mentor Joseph Utzschneider
added an epitaph "Approximativit Sidera"
which loosely translate to "He brought the stars closer".
Now, Utzschneider meant that Fraunhofer
brought the stars closer with his amazing glasswork
and his amazing telescopes
which you can still purchase if you have the cash,
but it turned out that his work
with the shadows in the sunlight
and the bright lights from his lamp
would bring the stars closer still
for they were the clue to solving an ancient mystery
which is, "What are the stars composed of?"
And how we know what the stars are composed of
is next time on the lightening tamers.
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Stay safe out there.
Bye.
Only video I've done so far
where a scientist was saved by a prince
and don't wait for princes.
They're not all that nice.
(laughs)
I've been watching "The Crown".
That's a bad idea.
Don't talk about princes when you watch "The Crown".
Definitely. Okay.
(laughs)
All right, too silly.