Last August 11 my wife and I found ourselves in the countryside of southern Hungary preparing to watch a total eclipse of the Sun. Luck was with us; an overcast, rainy morning gave way to clear skies an hour or two before totality began near midday. Although it wasn't our first total solar eclipse, we were nevertheless caught up in the fascination the event always brings: the increasingly eerie quality of the dying light as the moon relentlessly gnaws its way across the face of the sun, the expectant hush of the staring people around us, the sudden cries of awe as, in this case, the diamond ring phenomenon suddenly flashes into view. And with the closing darkness the local birds, true to form, set off to roost in the nearby trees, twittering in bewilderment at the early coming of night. I was immediately reminded of the story of Thomas Edison and the chickens.
It's a story that centers on the total eclipse of July 29, 1878, an eclipse notable on more than one historical front. I have already written about it (Marginalia, September–October 1994) in connection with the search for a putative planet, Vulcan, thought to revolve between the Sun and Mercury. Vulcan's presence, it had been hoped, would explain a discrepancy of about 40 arcseconds per century between theory and observation in the orbital motion of Mercury.
It was an eclipse well above average in interest to astronomers. The path of total eclipse, starting in Alaska, was to sweep down the spine of the Rocky Mountains and out across the Gulf of Mexico before ending in Cuba. This meant that it might be observed from an area with generally clear weather containing many high-altitude mountainous sites, mostly above the haze and water vapor that plague lower sites. This fact took on added importance in that the later 19th century was a time in which astrophysics, the study of stars themselves, as distinct from their positions and motions, was beginning an explosive growth. So it was that Samuel Langley, director of the Allegheny Observatory, intended to use these auspicious circumstances to further investigate the strange outer atmosphere of the sun called the corona. A recent theory at the time proposed that the corona, then visible only at a total solar eclipse, was the moon's atmosphere rendered visible by backlighting from the sun. Langley wanted to find out more about the corona and, in particular, its temperature. But how to measure the temperature of something 150 million kilometers away? The obvious thought was that if the corona is hot, as one would expect if it were solar, it must produce infrared radiation, albeit difficult to measure at that distance. This was a real problem for Langley, since existing thermopiles were generally too insensitive to yield a useful result. And it was here that Thomas Edison entered the story.
Edison Steps In
Edison, although only 31 at the time, was already the most famous inventor in the world, having the previous year invented the phonograph, which amazed people everywhere. Working at all hours, he directed a 12-man laboratory at Menlo Park, New Jersey, turning out astonishing inventions almost daily. He already held 89 patents in telegraphy alone, had invented the stock ticker and the carbon-button telephone, and had just that year announced the development of the incandescent light bulb, although it was really still a year from completion. But it was typical of Edison to make seemingly wild and certainly premature announcements. All in all he was a forceful and brash young man, and the popular press just loved him for it. To judge from the space accorded him in newspapers of the day, he must have had a reporter at his side almost daily.
By early 1878 he had, in fact, already been experimenting with a new invention that was particularly sensitive to heat and had discussed it briefly in correspondence with Langley. So it was to Edison that Langley turned in his quest for an instrument that could measure the corona's heat during the forthcoming eclipse. He noted that the necessary instrument would have to be at least 100 times more sensitive than existing thermopiles. Edison saw no difficulty in that. Langley's best thermopile was capable of detecting a change in temperature of about 10–4 degrees Fahrenheit, and Edison's new invention was already capable of about 4 x 10–5 degrees.
He called it a tasimeter, a name that took him more time and worry to invent than the instrument itself. Its basis was the carbon button, already developed as a transducer for telephones. The infrared radiation was focused onto a vulcanite rod. The heat caused the rod to expand and press against the button of powdered graphite. Since the electrical resistivity of powdered carbon is extraordinarily sensitive to pressure, the output of the instrument was read as a deflection of a galvanometer incorporated in an electrical circuit with the button. The thing certainly worked. Naturally there were demonstrations for the press, and Edison liked to show how easily the tasimeter could detect the heat from a person's hand 30 feet away. One correspondent found it to be so sensitive that "let a person come into the room with a lighted cigar, and it will drive the little animal wild." Edison's favorite demonstration was to show that the tasimeter was six times more sensitive to heat from his little finger than was a thermopile to a red-hot iron. After some further tweaking, Edison claimed the tasimeter had a sensitivity of 10–6 degrees Fahrenheit, and so met Langley's challenge. There is some doubt, however, as to whether Edison ever really made a sensitivity test in these terms.
But time was moving on, and Langley needed to make some astronomical tests before setting off to the eclipse. In early June he wrote Edison asking that the latter send a tasimeter to the Allegheny Observatory for tests, as well as additional carbon buttons for tests with other instruments. The carbon buttons arrived, but no tasimeter. Well into June Langley sent a reminder of the "promised tasimeter which I shall have great pleasure in testing." Then, "I expect to go in the beginning of July to observe the solar eclipse . . .," and finally, on July 5, just days before leaving, a terse telegram, "Send by express to Allegheny. I leave Monday." There was no reply from Edison.
What Langley didn't know was that Edison himself was going to the eclipse, armed with the tasimeter. Henry Draper, a wealthy medical doctor with an interest in astronomy, had invited Edison to join his party at the eclipse site in Rawlins, Wyoming Territory. Edison, in need of a break from Menlo Park, treated the trip as a vacation and gladly accepted.
He would travel free as a courtesy of the Union Pacific Railroad Company, which further provided him with a letter introducing him as "Mr. Edison, the celebrated inventor and telegrapher," and instructing telegraphers along the route to "send all messages of Mr. Thomas A. Edison free." The New York press turned out in full to see him off at the Pennsylvania Railroad depot and record his parting words:
"Yes," said Thomas Edison, "it [the tasimeter] will measure any degree of heat that can be measured. If the sun's corona has any heat of its own . . . the tasimeter will measure it accurately."
That evening the Daily Graphic devoted its full front page to Edison and the tasimeter.
En route to the Rockies Edison was accompanied by a correspondent of the New York Herald and hailed at every stop by the local press and railroad telegraphers, who regarded him as one of their own. Edison, one presumes, was never at a loss for a reply.
Rawlins, population 800, had been chosen as an eclipse site by some scientists since it was over 2,000 meters in altitude and, in particular, was readily available by train. Others, however, were spread up and down the mountain ranges, including Langley, 400 kilometers southward on the eclipse path at Pike's Peak, 4,300 meters high, still hoping to measure the coronal heat with a thermopile. All told, the astronomers observing the eclipse included some of the most illustrious names from around the world. They were doubtless unamused to find themselves summed up by the press in the phrase, "Professor Edison accompanied by a party of scientists . . .," especially since Edison was young, boastful, knew little astronomy and was not a professor to boot. Their feelings can be judged from the 500-page report on the eclipse eventually prepared by the U.S. Naval Observatory: The name of Edison appears nowhere in it!
Edison was more explicit regarding his contempt for most academics. He is on record with the statement "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." As for the mathematical sciences, "I can hire mathematicians at $15 a week but they can't hire me." He was scornfully amused at the precise latitude and longitude determinations made at the eclipse site: "It seemed to take an immense amount of mathematics. I preserved one of the sheets which looked like the timetable of a Chinese railroad."
One modern writer has described Edison at Rawlins as unwittingly like "a rather typical modern day eclipse-goer since (1) he made preparations only shortly before leaving, (2) he elected to defer final assembly and tests until arrival at the site, (3) he claimed success immediately after third contact, (4) he never reduced his data and (5) he never published his scientific findings." Which brings us finally to the chickens. This oft-told tale has been recorded by J. A. Eddy thus:
When Edison stepped off the train at Rawlins he found the professional astronomers already ensconced in the best rooms of the only hotel and already in possessive claim of the more protected places from which to observe the coming eclipse. All that remained for the tasimeter was a dilapidated hen-house, and in its doorway Edison set up his telescope and equipment. 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.
What degree of credence one can place in this story is highly uncertain; one suspects a good deal of gleeful embellishment with the passing years. Edison himself, dictating his memoirs some 30 years later, tells of setting up his equipment "in a small yard enclosed by a board fence six feet high; at one end there was a house for hens. I noticed they all went to roost just before totality. At the same time a slight wind arose and at the moment of totality the atmosphere was filled with thistle down and other light articles." This was the account that made the official biographies, of course, but the truth probably lies somewhere in between.
What is certain, however, is that Edison did in the end get a shot at the corona with his tasimeter. The New York Herald reporter, in his dispatch home, noted, "When but one minute of totality remained Edison succeeded in crowding the light from the corona upon the small opening of the tasimeter. Instantly the galvanometer cleared its boundaries. Edison was overjoyed." Edison himself, however, in later years faced up to the irony of having made too much of an improvement over existing detectors: "My apparatus was entirely too sensitive and I got no results."
Langley, by contrast, found himself once again the victim of an inadequate thermopile, which failed to detect the corona.
As for the tasimeter itself, it faded into obscurity rather rapidly. For a while there was talk of commercial applications (iceberg detector on ships, navigator's sun-finder in cloudy weather etc.), but it proved to be a slow, nonlinear, poorly repeating and highly unstable device. In short, great for qualitative demonstrations but useless for quantitative measurements. Edison got in a parting shot by dedicating it without patent to "the dilettantes in the higher branches of science."
Langley had his revenge by inventing the bolometer a couple of years later. Much better than a thermopile, it was less sensitive than the tasimeter, but it was stable, gave readings repeatable to one percent and could be used over a wider range of the spectrum. In announcing it Langley made no comparison with nor even mention of the tasimeter.
History perhaps had the last laugh. It was later pointed out that, during a total solar eclipse 36 years before the 1878 one, Professor Luigi Magrini, observing at Milan with an unusually sensitive thermopile on a reflecting telescope, had already measured a definite infrared signal from the solar corona. It had long been overlooked. Not, I suppose, that Edison would have cared much. Ninny stuff.
© J. Donald Fernie