Abstract
PROF. MARANGONI has lately experimented (Riv. Sci. Ind., March 15) on the diathermanous power of films of soapy water. A series of equidistant films (eight to ten) were produced in a wide vertical glass tube, and horizontal heat-rays from a smoked plate having a temperature of about 400 were directed down the tube by means of a metallic mirror, a second mirror below directing them to a thermopile communicating with a Weber magnetometer. The conclusions arrived at from the tabulated numbers are these: 1. The first of the films, notwithstanding its great tenuity, absorbs more than half the incident heat, reducing it (as expressed in the magnetometer deflections) from 38 to 18. 2. The successive films produce decrements, as theory indicates; the differences of their logarithms are sensibly constant (on an average 7.5), and the logarithms themselves, after the second film, decrease proportionally to the number of the films. 3. The diminution, of intensity observed must depend very little on reflection, but be due almost wholly to absorption. Indeed the first two films act like a sieve, intercepting, probably, the less refrangible rays in very large proportion, such as would hardly have been expected. 4. A given film becomes more diathermanous the thinner it becomes. 5. When various salts are mixed with the soap solution the diathermanous power is not sensibly affected. All these conclusions are in full agreement with the results of Melloni and with the theory of the phenomenon.
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Physical Notes . Nature 21, 620–621 (1880). https://doi.org/10.1038/021620a0
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DOI: https://doi.org/10.1038/021620a0