Prof. Norton on Molecular Physics. 437 



the electric equilibrium* ; and they are also sustained by the 

 fact of the close agreement that subsists between the conducting- 

 powers of the metals for heat and electricity. The analogy 

 between the conduction of heat and the conduction of a galvanic 

 current may be more fully stated thus : — A stream of heat con- 

 sists of two sets of pulses, viz. those conveyed by the electric 

 aether, and those conveyed by the universal aether ; and the pro- 

 pagation is attended with, and partly by means of, an induced 

 molecular polarization. The pulses propagated by the electric 

 sether tend to develope this polarization, which determines a 

 discharge of aether from one atmosphere to the next. But the 

 other set of pulses, in proportion as they are taken up by the 

 nearer side of the next atmosphere, tend to weaken the induced 

 polarization, and so to check the flow of the heat. A galvanic 

 current comprises two similar sets of pulses, is attended and 

 promoted still more effectually by a similar molecular polariza- 

 tion j and the absorption of the aethereal pulses, and their subse- 

 quent emission as heat, tends to check the flow of the current. 



The feeble conducting-power of many substances is probably 

 due to an aggregation of their particles in groups, with large 

 intervening spaces. The bad conductivity of gases and liquids, 

 both for heat and galvanic electricity, agreeably to the views just 

 offered, must be ascribed to a feeble polarizing action of one 

 particle upon another. This appears to be a consequence of 

 the peculiar state of the molecular atmospheres which deter- 

 mines the fluid condition (p. 279), combined with the effective 

 mutual repulsion of the particles in this condition. In the case 

 of liquids like water, whose ultimate molecules are compound, 

 a portion of the heat propagated should be consumed in expand- 

 ing the compound molecules. 



Capacity of Bodies for Heat. — The fundamental law discovered 

 by Dulong and Petit, that the specific heats of elementary sub- 

 stances are inversely proportional to their chemical equivalents 

 or atomic weights — or, in other words, that the atoms of such 

 substances have the same capacity for heat — if interpreted in 

 the language of the present theory, amounts to this, viz., what- 

 ever may be the difference of condition of the molecular atmo- 

 spheres of elementary substances, if the same amount of heat be 

 imparted to these atmospheres, the same amount will be given 

 off again and interchanged with surrounding bodies having the 

 same temperature. This would seem to imply that the portion 

 of the heat absorbed, which is consumed in expanding the atmo- 

 sphere, is the same for different simple molecules, and that the 

 remaining portion, which is taken up as new pulses by the atmo- 

 sphere, is also the same for molecules of different elementary 

 * See Dela Rive's Treatise on Electricity, vol. ii. p. 536 &c. 

 2F2 



