Eclipse Vicissitudes:Thomas Edison and the Chickens
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