Edisons Observations In Wyoming

In 1878, Edison was 31 years old. The year before he had invented the phonograph, which is widely regarded as the second best of his ideas, behind the incandescent electric light bulb. And there is evidence that the development of the light bulb was connected with the eclipse.

Edison had been working hard on a gadget known as a tasimeter to use during the eclipse. The basic concept of this device involves a small solid block having light shone on it from a certain source in the sky, selected by using a telescope with a screen or slit arranged such that only light from that source reaches the block. Any slight temperature change produced by the incoming radiation will cause the block to expand or contract, and the stress induced is a sensitive measure of the temperature variation. That stress or pressure can be measured electrically. It was reckoned that Edison's tasimeter could show a change ofjust one part in 50,000 of a degree Fahrenheit, and maybe even ten times better using an improved galvanometer. The idea was to try to measure the infrared radiation emitted by the corona, and so deduce its temperature.

Edison decided to combine his expedition to the eclipse with a month-long vacation in the western states. Leaving New York on July 13, he reached Laramie a week later and stopped to buy some hunting and fishing equipment. His spot for observing the eclipse was a hundred miles west, in Rawlins, Wyoming, along with various other parties who had used the Union Pacific railroad.

Unfortunately Edison made the mistake of setting up his equipment in a chicken coop. As the obscuration of the Sun progressed the chickens decided it was time to return to their boxes, getting under his feet at the critical stage, limiting the observations. He certainly got a reading, but did not have time to do much else. Edison should have read the Chinese annals of the thirteenth century: "The Sun was eclipsed; it was total . . .The chickens and ducks all returned to roost. In the following year the Sung dynasty was extinguished. "

At the start of August Edison headed onwards to San Francisco, also visiting Yosemite and various mines in the region to look into their ventilation and lighting requirements. He returned to Rawlins two weeks later to do some fishing, before heading on to Chicago and St. Louis. There he presented a paper on the tasimeter to the American Association for the Advancement of Science. On August 26 he returned to his laboratory in New Jersey, and the following day began his experiments on his electric light bulb. What is the connection with the eclipse?

In all Edison and his team of researchers tested something like six thousand different materials as possible filaments for the light bulb. (It was Edison who coined the term "filament" during these experiments.) Although they had many early successes, still the filament lifetimes were limited. It was not until 1897 that they settled on cotton thread that had been carbonized as the best they could do. In 1910 Edison's rival William Coolidge realized that a microscopically thin tungsten wire was much better, and that is basically what is still used in light bulbs today. In any case Edison's technique was limited by his insistence on using direct current, rather than the standard alternating current that soon took its place when the advantages were recognized.

Stepping back in time, Edison broke a bamboo fishing rod while angling near Rawlins and that night he threw it on the campfire. As he watched it burn he noticed how individual strands of the wood glowed white as they burned fiercely, and that convinced him that bamboo might be the best material to use for his light bulb filaments. His final solution, carbonized thread, is not much different.

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