. Elements of chemistry ... ical influence may be increasedto any desirable extent. Such an instrument is called athermo-electric pile. That used by M. Melloni in his ex-periments consisted of fifty-five bars of antimony, and asmany of bismuth, laid side by side, with their alternate -endssoldered together. Fig. 11 repre-sents this thermometer; «, the fjir. bars; b, a lamp heatingone end of the pile, by which theelectricity is developed, and themagnetic needle, c, is moved. Thelamp being removed, and the endof the pile blackened, in order topromote the absorption of the raysof heat
. Elements of chemistry ... ical influence may be increasedto any desirable extent. Such an instrument is called athermo-electric pile. That used by M. Melloni in his ex-periments consisted of fifty-five bars of antimony, and asmany of bismuth, laid side by side, with their alternate -endssoldered together. Fig. 11 repre-sents this thermometer; «, the fjir. bars; b, a lamp heatingone end of the pile, by which theelectricity is developed, and themagnetic needle, c, is moved. Thelamp being removed, and the endof the pile blackened, in order topromote the absorption of the raysof heat, the substances, whosepowers of transmission were to be examined, having been cut into thin plates, were placedbefore the end of the pile. A screen, having an apertureequal to the face of the pile, was placed between the source What is meant by thermo-electricity ? What effect does the thermo-electrical current have on the magnetic needle ? How is the thermo-electricpile constructed ? In what manner is the pile employed ?. SPECIFIC CALORIC. 35 of heat; and the plate to be tried, while a second screen in-tercepted the rays of heat until the instant of trial. 55. By such means, M. Melloni obtained very curious,and often very unexpected results; and, among others, thatbodies which transmit light most freely, often almost entirelyintercept the rays of heat, while other transparent bodiesare as permeable to heat as to light. 56. Bodies which allow the ready passage of heat, arecalled transcalent, or diathermanous, while those which in-tercept its rays are called intranscalent, or all substances, rock salt is most highly transcalent,admitting the rays of heat to pass through it with verylittle interruption; while alum, and glass, though fully aspervious to light as the salt, almost entirely intercept thecalorific rays, On the contrary, some substances, thoughnearly opaque, with respect to light, admit the passage .ofheat with considerable facility, such as brow
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