A text-book on chemistryFor the use of schools and colleges . ieties of radiant heat ? 1)2 82 RELATIONS OF HEAT AND LIGHT. cause which gives different colors to light, namely, thatheat, being an nnclulatory motion, has waves of variouslengths, and varying velocity of vibration. In the pris-matic spectrum the maximum of heat is found belowthe red end, and it steadily declines on passing towardthe violet. But in the interference spectrum, producedby a ruled grating, as discovered by Prof. Draper,the maxima of heat and light coincide, and are found inthe centre of the yellow. The prismatic s
A text-book on chemistryFor the use of schools and colleges . ieties of radiant heat ? 1)2 82 RELATIONS OF HEAT AND LIGHT. cause which gives different colors to light, namely, thatheat, being an nnclulatory motion, has waves of variouslengths, and varying velocity of vibration. In the pris-matic spectrum the maximum of heat is found belowthe red end, and it steadily declines on passing towardthe violet. But in the interference spectrum, producedby a ruled grating, as discovered by Prof. Draper,the maxima of heat and light coincide, and are found inthe centre of the yellow. The prismatic spectrum in-duces the supposition that heat is produced by slowerand longer vibrations than those of light, but the inter-ference spectrum corrects this hypothesis, and showsthat they coexist in the same place at the same time,and are probably one and the same force. Obscure heatis invisible light, and light, when extinguished, pro-duces heat. The apparatus by the aid of which Melloni prosecu-ted his extensive researches on heat is shown in Fig. 63. Fig. At M is a stand for the source of heat, with a concavemirror for concentrating the rays; at N, a perforatedscreen; at P, a plate of the substance to be examined;at T, a thermo-electric pile; at G, a galvanometer. Sis an unperforated screen that can be turned down, outof the way. What is the distribution of heat in the prismatic spectrum ?What is the distribution in the interference spectrum ? What is therelation between light and heat ? THEOEY OF EXCHANGES OF HEAT. LECTURE XVI. Theory of the Exchanges of Heat.—delations ofLight and Heat.—Theory of Exchanges.—Explana-tion of the Cold Ray Experiment. — Wellss Theoryof the Dew.— Cold on Mountain Tops.—Tempera-ture of the Sun.—Polarized Seat.—Heat of Chemi-cal Combination. The facts which militate against the doctrine of theunity of light and heat are, 1st, that the relations oftransparency for the two are not the same, smokyquartz or dark-colored mica allowing
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