Heat 



SCIENTIFIC SIDE-LIGHTS 



298 



1452. 



The Atomic Theory 



in Chemistry. As long as distance sepa- 

 rates [atoms or molecules] they can move 

 across it in obedience to the attraction; and 

 the motion thus produced may, by proper 

 appliances, be caused to perform mechanical 

 work. When, for example, two atoms of 

 hydrogen unite with one of oxygen, to form 

 water, the atoms are first drawn towards 

 each other they move, they clash, and then, 

 by virtue of their resiliency, they recoil and 

 quiver. To this quivering motion we give 

 the name of heat. This atomic vibration is 

 merely the redistribution of the motion pro- 

 duced by the chemical affinity; and this is 

 the only sense in which chemical affinity can 

 be said to be converted into heat. We must 

 not imagine the chemical attraction de- 

 stroyed or converted into anything else. 

 For the atoms, when mutually clasped to 

 form a molecule of water, are held together 

 by the very attraction which first drew them 

 towards each other. That which has really 

 been expended is the pull exerted through 

 the space by which the distance between the 

 atoms has been diminished. TYNDALI, Frag- 

 ments of Science, vol. i, ch. 1, p. 25. (A., 

 1897.) 



1453. HEAT AND ELECTRICITY Elec- 

 tric Conduction Increased by Cold Atomic 

 Theory of Electricity. If we make a com- 

 parison of electric conductors we find that 

 the metals that conduct heat best also con- 

 duct electricity best. This, it seems to me, 

 is a confirmation of the atomic theory of 

 electricity so far as it means anything. If 

 a good conductor, as silver, is subjected to 

 intense cold by putting it into liquid air, its 

 conductivity is greatly increased. It is well 

 known that heating a conductor ordinarily 

 diminishes its power to conduct electricity. 

 This shows that, in order that electrical mo- 

 tion of the atom may have free play, the 

 heat motion must be suppressed. ELISHA 

 GRAY Nature's Miracles, vol. iii, ch. 5, p. 47. 

 (F. H. & H., 1900.) 



1454. HEAT A RESULT OF MOTION 



Water of Cataract Warmed by the Fall 

 Ocean Made Warmer by Storm. This small 

 basin contains a quantity of mercury which 

 has been cooled in the next room. One of 

 the faces of the thermo-electric pile is 

 plunged into the liquid metal. The deflec- 

 tion of the needle proves that the mercury 

 is cold. Two glasses are swathed thickly 

 round with listing, to prevent the warmth 

 of the hands from reaching the mercury. I 

 pour the cold mercury into one of the 

 glasses, and then from the one glass into 

 the other, and back. Its motion is de- 

 stroyed, but heat is developed. The amount 

 of heat generated by a single pouring out is 

 extremely small; so we will repeat the 

 process ten or fifteen times. The pile being 

 now plunged into the liquid, the needle 

 moves; and its motion declares that the 

 mercury, which at the beginning of the ex- 

 periment was cooler, is now warmer than 

 the pile. We here introduce into the lec- 



ture-room an effect which occurs at the base 

 of every waterfall. There are friends be- 

 fore me who have stood amid the foam of 

 Niagara, and I have done so myself. Had 

 we dipped sufficiently sensitive thermometers 

 into the water at the top and at the bottom 

 of the cataract, we should have found the 

 latter warmer than the former. The sailor's 

 tradition, also, is theoretically correct; the 

 sea is rendered warmer by a storm, the me- 

 chanical dash of its billows being ultimately 

 converted into heat. TYNDALL Heat a Mode 

 of Motion, lect. 1, p. 6. (A., 1900.) 



1455. HEAT DEVELOPED BY CHEM- 

 ISTRY AND ELECTRICITY It has already 

 been stated that chemical changes develop 

 electricity; which, in its turn, becomes a 

 powerful disturbing cause. As a chemical 

 agent, says Davy, its silent and slow opera- 

 tion in the economy of Nature is much more 

 important than its grand and impressive 

 operation in lightning and thunder. It may 

 be considered not only as directly producing 

 an infinite variety of changes, but as influ- 

 encing almost all which take place ; it would 

 seem, indeed, that chemical attraction itself 

 is only a peculiar form of the exhibition of 

 electrical attraction. LYELL Principles of 

 Geology, bk. ii, ch. 31, p. 542. (A., 1854.) 



1456. HEAT, FRICTION AN INEX- 

 HAUSTIBLE SOURCE OF Count Rumford's 

 Argument. With Rumford, however, a new 

 and powerful factor appeared on the scene. 

 He began by proving the hypothetical mat- 

 ter of heat to be imponderable, but the main 

 drift of his experiments was to prove fric- 

 tion to be an inexhaustible source of heat, 

 while the whole force of his logic went to 

 show that an inexhaustible emission is ir- 

 reconcilable with the notion that heat is a 

 kind of matter. TYNDALL Heat a Mode of 

 Motion, lect. 2, p. 39. (A., 1900.) 



1457. HEAT OF EARTH, LOSS OF 



No Sensible Diminution in Two Thousand 

 Tears. The gradual diminution of the sup- 

 posed primitive heat of the globe has been 

 resorted to by many geologists as the prin- 

 cipal cause of alterations of climate. The 

 matter of our planet is imagined, in accord- 

 ance with the conjectures of Leibnitz, to 

 have been originally in an intensely heated 

 state, and to have been parting ever since 

 with portions of its heat, and at the same 

 time contracting its dimensions. There are, 

 undoubtedly, good grounds for inferring 

 from recent observation and experiment that 

 the temperature of the earth increases as 

 we descend from the surface to that slight 

 depth to which man can penetrate: but 

 there are no positive proofs of a secular de- 

 crease of internal heat accompanied by con- 

 traction. On the contrary, Laplace has 

 shown, by reference to astronomical observa- 

 tions made in the time of Hipparchus, that 

 in the last two thousand years at least there 

 has been no sensible contraction of the globe 

 by cooling ; for had this been the case, even 

 to an extremely small amount, the day 



