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HOME > PAST ISSUE > May-June 2000 > Article Detail

MARGINALIA

Eclipse Vicissitudes:Thomas Edison and the Chickens

J. Donald Fernie

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.

Figure 2. Tasimeter is now preservedClick to Enlarge Image

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.





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