From the Library: Solar Cooker

Here’s another “what is it?” from the image collection:

Vertical Access Solar Furnace at Fuller Road Laboratory, ca. 1970s

If you’re like me, you associate the phrase “solar cooker” with a summer camp construction project made out of cardboard and aluminum foil, used to toast a marshmallow.  But that’s not the limit of solar ovens.  At the extreme end of the range, the Odeillo solar furnace is southern France is capable of producing temperatures of  3,500 °C.  Or course, it’s over 50 meters tall.  Still, much more modest solar furnaces are still capable of producing usefully high temperatures.

This device, called a vertical access solar furnace, could focus sunlight into the small dome seen in the center.  A small sample of material could be placed in the center dome, and it would then be subjected to a beam of extremely powerful light capable of heating the sample to high temperature.  I haven’t found a record of how hot it could go, but a slightly larger version of this device in Texas managed 3,000 °C.  These temperatures could simulate the  extreme conditions that particles could experience in space or when entering the earth’s atmosphere.

From the Library: “A Plan for Securing Observations of the Variable Stars”

Pamphlets were the blog posts of the nineteenth century.  They could be quickly and cheaply produced, then distributed either for free or for a few pennies to cover printing costs.  If popular, they could be bound and go from being ephemera to being permanent.  One fan of the preserving the media, Samuel Johnson, explained the appeal:

From pamphlets, consequently, are to be learned the progress of every debate; the various state [sic] to which the questions have been changed; the artifices and fallacies which have been used, and the subterfuges by which reason has been eluded; in such writings may be seen how the mind has been opened by degrees, how one truth has led to another, how error has been disentangled …

“De stella β lyrae variabili disquisitio” (Discussion of variable star Lyrae β) Argelander, Friedrich, 1844

Because of their quick production, pamphlets could be part of larger discussion, and so they let us see the discussion in motion instead of in retrospect.

The wide reach and low cost of pamphlets made them useful in another way: a person who  didn’t have a lot of money could still get the word out.  Enter Edward Pickering, director of the Harvard Observatory.  In 1882, he was running out of money.  He had tried everything, from soliciting donation to selling the lawn clippings, but there were always more demands than there was money to hire staff.

At that point, he was particularly interested in variable stars.  These stars appear to pulse; they brighten and dim in a regular pattern with a period that can last for seconds or years depending on the star. Interest in these stars seems to start with German astronomer Friedrich Wilhelm Argelander, and came to America through one of his students, our own Benjamin Gould.

Of course, figuring out the variable brightness and the length of the period of a variable star requires making hundreds of observations over a long stretch of time.  Most astronomers don’t have the kind of time. Gould hit upon the idea of inviting amateur astronomers to pitch in.  He made a call through his publication, the Astronomical Journal, asking for assistance.  He, and his student Seth Chandler, publish pamphlets instructing people on how to record their observations of a variable star.

Pickering borrowed that idea.  In 1882, he published a pamphlet, “A Plan for Securing Observations of the Variable Stars.”   For the most part Pickering followed the same approach as Gould and Chandler.  But there was one major addition:

“Much valuable assistance might be rendered by a class whose aid in such work has usually been overlooked. Many ladies are interested in astronomy and own telescopes, but with two or three noteworthy exceptions their contributions to the science have been almost nothing. Many of them have the time and inclination for such work, and especially among the graduates of women’s colleges are many who have had abundant training to make excellent observers. As the work may be done at home, even from an open window, provided the room has the temperature of the outer air, there seems to be no reason why they should not thus make an advantageous use of their skill. It is believed that it is only necessary to point the way to secure most valuable assistance. The criticism is often made by the opponents of the higher education of women that, while they are capable of following others as far as men can, they originate almost nothing, so that human knowledge is not advanced by their work. This reproach would be well answered could we point to a long series of such observations as are detailed below, made by women observers.”

“A Plan for Securing Observations of the Variable Stars,” Edward Pickering, 1882

Pickering had hired Williamina Fleming as a computer the year before, and she became the first of the women we now call  the “Harvard Computers.”   In this little pamphlet we can see the potential working itself out in Pickering’s head.

That little teaser at the end – “here’s your chance to prove them wrong” – actually came to pass.  In 1908, one of Harvard’s Computers named Henrietta Swan Leavitt was able to work out the relationship between the brightness of a variable star and the period of its bright/dim cycle.  This meant that an astronomer could know the actual brightness of a variable star, and using the amount of the light that makes it to earth work backwards to determine the distance.  This discovery was essential for working out the size of our universe.

These pamphlets, from Argelander, Chandler and Pickering, are part of Dudley’s pamphlet collection.  We owe a debt to Katherine Brent, student at the University at Albany’s Library Science program and associate librarian at SUNY Cobleskill, for her work arranging and describing this incredibly valuable collection.

Edison and the Eclipse: Chickens Come Home to Roost

I mentioned the eclipse of 1878 a couple of weeks ago.  I am now required by the historian’s code of ethics and the miSci by-laws to mention the stories around Edison’s trip out to Wyoming.

There are a lot of stories.  At the age of 31, Edison was already a folkhero.  Some of it stemmed from his invention of the phonograph.  More of it came from the press.  Edison was good copy; he was quick with a quip or an eye-catching pull quote, and he carefully played the everyman as opposed to the egghead.

Edison’s close relations with the press may have backfired on him in 1875.  After discovering what he thought to be a new phenomenon caused by a vibrating magnet, he announced his finding in the newspapers rather than to the scientific community.  This was a violation of the unwritten rules of science: you don’t issue a press release until after your scientific peers have had a chance to look at your results.  When his discovery was pronounced to be nothing new, Edison looked foolish before the whole community, and he didn’t take the embarrassment well.

Edison doubled down on the anti-intellectualism.  A number of choice quotes come from this period:  “I wouldn’t give a penny for the ordinary college graduate, except those from Institutes of Technology . . . they aren’t filled up with Latin, philosophy, and all that ninny stuff.”  And my favorite, “I can hire mathematicians at $15 a week, but they can’t hire me.”

Edison’s Tasimeter

All of which raises the question of why Edison was tagging along to Wyoming with all the scientists.  Edison had invented a new device called the tasimeter, a clever bit of engineering that used a carbon button [c] and a vulcanite rod [A] to detect small changes in infrared radiation.  The ultimate test for such a device would to measure the heat of the solar corona, which was best done during an eclipse.  The 1878 Eclipse was just in time, so after taking a quick trip to Austria to steal the tasimeter from Nikola Tesla (kidding, kidding), he headed for Wyoming.

Edison’s folksy quips didn’t endear him to the scientists, which maybe explains some of the stories that come down.  Some are innocuous, like the story recorded by Wyoming historian Phil Roberts, in which Edison does some stargazing and comes up with the idea for the electric lightbulb.  Since the bulb already existed by that point, the story in unlikely.

Most of the stories have fun at Edison’s expense.  The most often repeated is the story of the drunken cowboy who barged into Edison’s room late at night, intent of showing the famous inventor how well he could shoot.  This story comes to us from Edison’s own mouth, as recorded by his biographer Frank Lewis Dyer:

“There were astronomers from nearly every nation,” says Mr. Edison. “We had a special car. The country at that time was rather new; game was in great abundance, and could be seen all day long from the car window, especially antelope. We arrived at Rawlins about 4 P.M. It had a small machine shop, and was the point where locomotives were changed for the next section. The hotel was a very small one, and by doubling up we were barely accommodated. My room-mate was Fox, the correspondent of the New York Herald. After we retired and were asleep a thundering knock on the door awakened us. Upon opening the door a tall, handsome man with flowing hair dressed in western style entered the room. His eyes were bloodshot, and he was somewhat inebriated. He introduced himself as ‘Texas Jack’—Joe Chromondo—and said he wanted to see Edison, as he had read about me in the newspapers. Both Fox and I were rather scared, and didn’t know what was to be the result of the interview. The landlord requested him not to make so much noise, and was thrown out into the hall. Jack explained that he had just come in with a party which had been hunting, and that he felt fine. He explained, also, that he was the boss pistol-shot of the West; that it was he who taught the celebrated Doctor Carver how to shoot. Then suddenly pointing to a weather-vane on the freight depot, he pulled out a Colt revolver and fired through the window, hitting the vane. The shot awakened all the people, and they rushed in to see who was killed. It was only after I told him I was tired and would see him in the morning that he left. Both Fox and I were so nervous we didn’t sleep any that night.”

A more embarrassing story comes down from a shipping agent in Separation, Wyoming named John Jackson Clarke, recounted in Thomas Levenson’s wonderful book “The Hunt for Vulcan.”  Apparently, Edison’s comment about “game in great abundance,” wasn’t just an idle note.  He intended to bring home a trophy:

Edison returned to the station first, and he asked whether there might be anything else worth shooting nearby. Clarke told him that the surrounding plain enjoyed an abundance of jackrabbits—”what the locals call narrow-gauge mules:’ Edison asked where he might find them, and Clarke “pointed west and noticing a rabbit in a clear space in the bushes, said there is one now.”

Edison picked out a silhouette from the platform, but he wanted to make sure of his kill. He “advanced cautiously to within 150 feet and shot.”

The animal did not move. He closed to one hundred feet. He fired again.

The beast wouldn’t jump. He aimed, pulled the trigger once, and then again.

His target stood its ground. Edison glanced over his shoulder and saw that the entire station staff had gathered for the show. The penny dropped.

He’d been set up, played for a dude. His target looked like a desert hare, all right, all ears and legs. It was exactly where one might expect to spy such an exotic creature.

And yet … Thomas Edison, genius, had just murdered … a stuffed jack-rabbit.

Probably the most famous story comes down through as astronomical community, notably from astronomer John A. Eddy.  According to that story, Edison’s late arrival at the viewing site meant that the choice places to set up instruments were already taken.  He was forced to set up his tasimeter in a chicken coop:

In the afternoon of 29 July, as totality neared, a brisk Wyoming wind arose, filling the darkening sky with dirt and debris. These conditions made the balancing of the tasimeter . . . especially difficult, and with the onset of darkness at second contact, the tasimeter was still not adjusted. Only two minutes of totality remained. Feverishly he worked, but alas! With the sun covered and sky dark, the chickens came home to roost, through Edison’s observatory door, past the telescope, in, around, and over the frantic inventor. Uninitiated in astronomy, he had failed to allow for a fundamental eclipse phenomenon.

All these stories make for an embarrassing trip for Edison.  But worst is probably the fact that the tasimeter didn’t work.  It was either too sensitive or not sensitive enough, and it failed to detect the heat from the solar corona.  Unfortunately, the tasimeter would go down in history as one of Edison’s more interesting failures.

Dr. Boss and the Martians

By now, you’ve probably seen our Outreach Astronomer, Dr. Rapson, talking about the new discovery of exoplanets around the TRAPPIST-1 system.  Or maybe you’ve heard her talking about the coming solar eclipse, or the discovery of water on Mars, or any of a number of astronomical topics.  She’s fulfilling a role that the representatives from Dudley have played for over a century: explaining new developments in astronomy to the public of the Capital region.

Of our directors, Dr. Benjamin Boss was the most active public scientist.  Local papers frequently went to his to deliver an explanation or a verdict.  And it wasn’t always restricted to astronomy; when an earthquake shook Albany in October, 1935, Dr. Boss could be found in the Albany Times-Union explaining fault lines.

And sometimes, he could be found crushing a dream …

Albany Times-Union, November 12, 1931

The gist of the article is that a group of scientists were speculating on a rocket trip to Mars.  The TU turned to “internationally noted authority on astronomy” Benjamin Boss.  Boss explained some of the difficulties: the duration of the trip and the need for supplies and oxygen, the damage that could be inflicted by the velocities at take off and the velocity on hitting Mars, and the fact that there would be no obvious way back.

Apparently the editors of the TU decided to run through their clippings file on Mars and include whatever pictures they found. The “martian” is Oamaruru, the martian woman who was supposedly in psychic contact with Dr. Hugh Mansfield Robinson in the 1920s.  That raises questions about who these scientists planning a trip to Mars actually are.

(“But all these dreams are shattered by Dr. Benjamin Boss, noted astrologist …”  I dare you to call Dr. Rapson an “astrologist.”  Just wait until I’m in another room.)

From the Collection: Velocity Model

Image collections can be an entertaining headache.  Imagine someone going through the shoebox of old photographs that your parents keep in the closet and trying to figure out each picture.  Sometimes the subject of the photo will be obvious. Other times it will be something that no one will ever be able to puzzle out without having been there.

Dudley has a modest collection* of glass plate negatives from the time of Benjamin Boss.  They seem to be part of Boss’s personal collection, so the shots of galaxies and lunar eclipses are mixed in with his wedding photographs and pictures of his children.  And there are also several pictures of whatever this thing is:

Galactic Velocity Model

The images were only labeled  “velocity model,” which isn’t very helpful.  It took a lot of digging, but eventually I stumbled across this bit from an interview with Boss:

Aided by an ordinary box which he had constructed, Dr. Boss was able to demonstrate the startling bit of news that the Milky Way actually spins or rotates.

Dr. Boss had ingenuously stretched fine lengths of thread between the top and bottom side of the box and upon which were fixed small beads. Dr. Boss pointed out that each small bead attached to the thread represented a star in the Milky Way. The entire cluster of beads suggested that they had been scattered, as a farmer scatters seed within the 180 degree angle. Dr. Boss then said that, were it possible to bring all the stars in the Milky Way into a small cluster to be held or fixed and then released for one minute and then fixed again, the stars in the Milky Way would appear in relatively the small positions he had arranged the beads. This, Dr. Boss said, proves to his satisfaction that Milky Way with its more than 30 billion stars is in reality a spinning or rotating mass.

– Albany Times-Union, Nov 24, 1935, p.2-B

Dudley’s major function during early twentieth century was creating a catalog of star positions and velocities.  This kind of work can be dismissed as boring “stamp collecting,” but it lead to some major scientific discoveries.  Here Benjamin Boss was using a simple model to show the three-dimensional position of stars within our galaxy to show how their motion leads to the realization that the whole galaxy is rotating.


(*) Bear in mind that I’m sitting next to miSci’s collection of GE photographs.  With 1.6 million photographs and negatives, it’s one of the largest image collections in the world.  In this building, anything that doesn’t fill a room will be considered “modest.”

The Total Eclipse of 1878

Harper's Weekly, July 1878 Eclipse

Harper’s Weekly, July 1878 Eclipse

As we gear up for the Eclipse Across America this summer, it’s worth looking back at the history of eclipse viewing and the role it played in modern astronomy.  Treks out to some remote location to view a solar eclipse were a type of pilgrimage for American astronomers, bringing together large numbers of scientists in one remote location.  Questions were answered, rivalries were struck, scores were settled and a lot of good science was accomplished.

One of the most interesting was the solar eclipse of July 1878, which allowed several old friends (and enemies) to settle one of the most vexing questions of 19th century astronomy.

The path of the 1878 eclipse made it visible from Alaska down through the Rockies and then into the Gulf of Mexico and Cuba.  There were a number of sites in its path that would be ideal for viewing: dry, elevated and dark.  Even better: the decade old transcontinental railroad ran out to the path of the eclipse, meaning that astronomers could take along all the bulky equipment they could ship.

So the scientific community boxed up their gear and headed out to Rawlins, Wyoming, where the total eclipse would be visible for two minutes, fifty-six seconds.  Along for the trip were men like Simon Newcomb of the Naval Observatory, soon to become possibly the most famous astronomer in America.  Also in attendance was Norman Lockyer, founder of the journal Nature, and James Craig Watson of the Ann Arbor Observatory.

And also a 31 year old tinkerer named Thomas Edison, but that’s another story.

The eclipse viewing crew, led by Henry Draper.

The eclipse viewing crew, led by Henry Draper.  Edison is second from the right.  The two women are Mrs. Draper and Mrs. Watson.  It’s nearly impossible to identify the rest of the mustached mass of men.

There was a great deal of scientific work to be done in the just-under three minutes of the eclipse, but the goal that caught the popular attention was the search for the hypothetical planet Vulcan.  

The French mathematician Urbain Le Verrier had theorized the existence of this small planet in between Mercury and the Sun during the mid 19th century.  Many astronomers considered it the most likely explanation for certain irregularities in the orbit of Mercury.  But finding it had proved difficult. Many astronomers had caught fleeting glimpses of something in the right vicinity – asteroid, sunspot or maybe a small planet.

The search for Vulcan had taken on a new urgency after an eclipse in 1869, thanks to our own Benjamin Gould.  After leaving Dudley, Gould had become one of the early astronomers skilled in photo-astronomy.  He set up his equipment in Burlington, Iowa, during the eclipse in order to photograph the solar corona.  On the right bank of the Mississippi he snapped forty two images of the eclipse.

Gould reasoned that if there was a planet orbiting between Mercury and the Sun, then it should be visible in the shadow of the eclipse.  He examined his own photographs, plus over three hundred other photographs of the eclipse, and came to the conclusion that nothing was there.  Not a man for mincing words, Gould announced, “I am convinced that this investigation dispenses with the hypothesis that the movement of the perihelion of Mercury results from the effects of one or many small interior planets.”

For Gould, the matter was settled.  But popular theories don’t die that easily.  For a while, most astronomers continued to find nothing.  Then in April, 1876, a German astronomer working in northern China named Heinrich Weber sent a telegram back to Europe announcing that he had seen a circular object in transit across the Sun.  Once again, the game was afoot.

America was still struggling to catch up to Europe in the realm of science. Many in the American scientific community would have loved to find Vulcan from a spot on American soil.  So many of those tromping out to Wyoming were hoping to be the one to spot the rogue planet.  

In the end, the verdict was mixed.  Most of the astronomers, including Newcomb, had found nothing.  Watson had, and Watson was a well respected observer.  He also seemed to be supported by Lewis Swift, an amateur astronomer from Rochester who had been observing the eclipse in Denver.  

Rochester has produced many fine astronomers, but in the end it came down to what Watson believed he saw.  Surprisingly, Benjamin Gould’s verdict on Vulcan ended up being supported by his arch-nemesis – and fellow Dudley alumni – Christian F.H. Peters.  After leaving Dudley, Peters had ended up at Hamilton College are racked up an impressive number of asteroid discoveries.  He had been a Vulcan skeptic since the beginning, and he left no doubt that he believed Watson had made some basic errors in his supposed sighting.

While the journal Nature chided Peters for his tone, few seemed eager to defend Watson’s observations.  After the bulk of the astronomers viewing the 1878 eclipse reported no luck in spotting Vulcan, the pendulum seems to shift towards skepticism.  The problems with Mercury’s orbit remained, but the search for Vulcan drifted to a close.  In 1915, Albert Einstein was able to use his new theories of gravitation to accurately predict the orbit of Mercury, ending any need for another planet and closing the debate.

Goulds all the way back

There’s one advantage to inheriting a library; you don’t just get the books, you also get the bookmarks.  This bit of paper was found in one of the books used by Benjamin Gould.  On one side are some calculations.  On this side is a rough family tree.

Like any good Boston pure-blood, Gould was very interested in his own genealogy.  I know we’ve got some fans who can trace their lineage back to Gould’s family, so I thought this might be useful.

In the third column, the John Gould that is married to Sarah Parker would probably be Lieutenant John Gould (1635-1710), who served during King Phillip’s War.  Since he had eight children, you can see that this listing is very partial.

Benjamin A. Gould Family Tree (Gould Papers, B6,F6)

Benjamin A. Gould Family Tree (Gould Papers, B6,F6)

I’m afraid that all future generations will find in my books are the backs of Netflix envelopes and old receipts.  I feel like I’m failing history.


grand theodoliteIn regards to the last post, here’s Verplanck Colvin himself, taking notes on the right.  The instrument he’s using is called a theodolite, which is essentially a small rotating telescope for measuring horizontal and vertical angles.  Well, I guess in this case it’s not really a small telescope at all.  That looks like a brass telescope, maybe 4″ or so.

Colvin called this his “grand theodolite,” and last I checked, no one was sure where it had ended up.  Such a big and impressive big of technology porbably wasn’t scrapped (although, given that he and his crew had to hump this thing up and down a mountain, they probably wanted to).  If anybody has any idea, I’d love to know what happened to it.













barometerHere’s a less portable piece of technology.  This is George Washington Hough’s “automatic registering and printing barometer.”  It was Hough’s pride and joy.  He the bulk of the second Dudley annals describing it and showing tables of its results.

The object labeled B is a cylinder of mercury attached to a support frame that is bolted to a brick wall in the observatory.  A float is suspended in the mercury which rises and falls reacting to changes in the air pressure.  Changes in the position of the float trigger electromagnets, which release gears in the mechanism and cause the pen arm, S, to change position to match the float.  A drum wrapped in paper, O, rotates against the pen, recording a steady line that peaks and dips with the pen arm.

The weights at the bottom power the gears and the drum.  A battery powers the electromagnets.  By using batteries just to lock and unlock the gears, the use of electricity could be kept to a minimum.  Important in an are where recharging batteries required refreshing the chemicals.

Obviously it’s more complicated than I’m making it sound, but Hough was able to make it work.  It’s probably worth mentioning that when Hough was laid off in 1873, he went into private business selling his own inventions and was apparently successful.

How to Measure a Mountain Without Leaving Your Observatory

Nineteenth century observatories were more than just places to look at the stars.  They were packed with scientific instruments that were useful for all sorts of purposes: highly accurate clocks, barometers, thermometers, transits and other surveying equipment, and so on.  Many observatories were staffed by people eager to reach out to the public, either as part of their mission or to justify their funding.  Observatories could become little temples of science for their community.

As a rare privately funded observatory unattached to a university, Dudley had (and has) a strong need to be useful to the community which created it.  I’ve mentioned Benjamin Gould’s plan to provide accurate time for New York.  Since time is a measure of the earth’s rotation, the observatory could help mapmakers determine longitude. Dudley also offered public viewings to all, right through the Civil War.

Here’s one interesting example of Dudley making its scientific resources available.  In 1870, the naturalist and engineer Verplanck Colvin was working on a geological survey of the Adirondack region.  As part of this project he completed the first recorded ascent of Seward Mountain.  To complete his survey, he needed to know roughly how tall the mountain was.

One way to work out the height of a mountain was to take barometric readings at the top.  Since air pressure is lower the higher you climb, you can compare those numbers with readings taken from close to sea level.  By working out the difference, you can figure out the difference in elevation.

For the best accuracy, the readings should be from the same region and at the same time.  But synchronizing time can be a little tricky when you’re on the side of a mountain.  Fortunately for Colvin, in 1870 the head of the Dudley Observatory was George Washington Hough.

Hough was not only an astronomer, but also an inventor.  And his pride and joy was a self-reading and printing barometer, which could keep track of changes in the barometric pressure and keep record of when they happened.  So when Colvin came down from the mountain, he could send his notes to Hough, who would compare Colvin’s readings with his own records from the appropriate time.

Colvin took the results and presented a report at the Albany Institute.  Fortunately for us, he included the text of the letter he received from Hough:

Letter from George Washington Hough to Verplanck Colvin

Letter from George Washington Hough to Verplanck Colvin

The result was significantly lower than previous estimates, but not far off of the current measurements.  It’s a small thing, but it helped establish Colvin as a serious surveyor and helped him gain funding for his continued work in the Adirondacks.  And that is important for New York, because Colvin became the father of the Adirondack Park.

Immediately after this presenting this letter, Colvin began to describe the damage caused by lumbering that he had seen from Seward Mountain.  He proposed that the Adirondacks become a state park to protect the forest.  He cleverly tied the preservation of the forest land, which shielded lakes and snow packs, with the need for water in the Erie Canal.  It became a major theme of his work.  When he was later appointed the superintendent of the New York state land survey, he oversaw the creation of the Adirondack Forest Preserve in 1885.

Making New Mirrors

Proof of Concept for Silica Mirror (Thomson Papers, B#6, F001)

Proof of Concept for Silica Mirror, 36″ (Thomson Papers, B#6, F001)

This doesn’t look like much, but it was the start of something that was going to revolutionize the field of astronomy.  This is a disk of silicon dioxide, also known as silica.  Since it is made from very clean quartz sand, it is also known as “fused quartz”.  You can think of silica as being very pure glass without any additives.

Those additives serve a purpose.  They lower the melting temperature of the silica.  Without those, silica can require a furnace at 3,000 degrees Fahrenheit to work with.  But removing those additives means that you have a type of glass that is very resistant to changes in temperature.

One of the first people to see the advantages in this was Elihu Thomson, a scientist, engineer and businessman who founded the Thomson-Houston Electric Company.  This company later merged with Edison General Electric to create the General Electric company we’re familiar with today.

Since fused quartz is so resistant to heat, it has been used in high temperature applications like halogen lamps and furnaces.  It’s strong, so it has been used in bathyspheres and other high-pressure devices.  But Thomson was an avid amateur astronomer, and he saw a use for silica that others might have missed: telescope mirrors.

Since silica resists changing shape with heat, it could be used in unheated observatories that could get blistering hot or freezing cold without distorting the viewing.  It could also resist the heat produced by grinding and polishing, which made it easier and faster to work with that regular glass.  Mirrors could be produced faster and – more importantly – larger than ever before.

In the late 1920s, when George Hale convinced the Carnegie Institution to fund the construction of a new telescope for the Palomar Observatory, he was thinking big.  Hale had already worked on the largest telescope in the world: the 40-inch refracting telescope at Yerkes Observatory, 60-inch Hale reflecting telescope at Mount Wilson Observatory and 100-inch Hooker reflecting telescope at Mount Wilson.  For his next – and final – telescope, he would require a massive 200 inch mirror.

This was probably beyond the conventional technology of the time.  Hale needed to try something new.  He ended up turning to Elihu Thomson and his idea for a fused silica mirror.

The lump at the upper right was a proof of concept.  The next mirror would be a sixty inch disk, and no one had worked with silica on that scale before.  It required new techniques and the construction of new furnaces in Thomson’s Lynn, Massachusetts plant.

Construction of a experimental furnace for the 60-inch Palomar Mirror (Thomson Papers, B#6, F006a)

Construction of a experimental furnace for the 60-inch Palomar Mirror (Thomson Papers, B#6, F006a)

In the end, it took three years to produce two sixty-inch mirror.  The first mirror was of excellent quality, but it cracked during the cooling process.  The second mirror was marred by air bubbles.  Thomson and  General Electric had proven that large scale silica mirrors could be made, but that wasn’t enough.  Hale needed something produce quickly, and at a reliable price.

So the 200-inch mirror was not made in a Schenectady factory, but in Corning Glass works.  And instead of silica, it was made of Pyrex.  One of the first attempts at the 200-inch mirror is on display at the Corning Museum of Glass.

It’s a little frustrating, but it’s a good example of the difference between a new technology and a more mature technology.  Pyrex had been invented in the 1890s, about the same time that Thomson began experimenting with fused quartz.  But Thomson was a businessman, and a busy one.  There was no immediate need for silica mirrors, and the potential market seemed small.  General Electric had plenty of other things to do.

Corning invested more time and energy into Pyrex, and so they went into the process with more confidence.  They succeeded in six months when GE it had taken three years to not quite pull it off.