PHYSICS 117 



boron, and silicon. At temperatures from 100 abs. downwards there is a rapid fall 

 in atomic heats, which tend to zero as the absolute zero of temperature is approached. 

 This observation forms the raison d'etre for the theory of heat quanta propounded by 

 Einstein and worked out more fully by Nernst, 1 which differs from Planck's (revised) 

 theory by postulating not only a unitary emission, but also a unitary absorption of 

 energy, a modification for which E. Bauer has recently (1912) advanced some fur- 

 ther theoretical reasons. 



The smallness of specific heats near absolute cold is then accounted for somewhat 

 as follows. Near o abs. only very few atoms will possess any quanta of energy, but 

 the few that do will determine the temperature of the aggregate. The remainder are 

 simply at rest. Therefore a very small quantity of heat suffices to raise the apparent 

 temperature of the body, in other words, its specific heat is small. 



But this is only one of many useful applications of the theory. It enables us to 

 calculate not only specific heats, but melting points and heats of transformation, besides 

 giving a quantitative expression for chemical affinity. The atomic frequency v, which 

 enters into all the formulae, is calculated either from absorption spectra, or from the 

 selective photoelectric effect, as in the extensive work of Pohl and Pringsheim; or the 

 cubic elastic compressibility. And Lindemann 2 gives the formula v = 4.sgXio lb ^nd/A, 

 where A is the atomic weight, n the valency, and d the density of the body. 



F. Haber, 3 who defines Planck's action constant h as " the amount of work required 

 to extract an electron from an atom or molecule having a frequency of i vibration per 

 second," deduces the relation vt=Vv^mlM., where Vi, v v are the infra-red and ultra- 

 violet frequencies respectively, m is the mass of an electron, and M that of the atom. 



The Revival of " Caloric." How far the " materialising tendency" has proceeded 

 in recent years is evidenced in a striking manner by Prof. H. L. Callendar's opening 

 address to Section A of the British Association at Dundee, in which he pleaded, if not 

 for a revival of the caloric theory of heat, at least for a recognition of the legitimate 

 claims of some of its leading principles. The materiality of heat cannot be refuted 

 by weighing if it consists of electrons whose mass is purely electromagnetic, or, better 

 still, if it consists of doublets of positive and negative electrons, which would have rto 

 perceptible weight, no evident electrical properties, and no absorbing power for light. 

 They might even constitute the aether of space, which, as Witte has shown, must not 

 be a continuum, but have a discrete structure, if it is to exist at all. At all events, caloric 

 would have a physical existence, instead of being merely the logarithm of a probability. 

 It would be identical with entropy. 



In this connection an observation by L. Dunoyer (1911) may be of interest. He 

 finds that in very high vacua the vapours of potassium and sodium are precipitated 

 on the walls of the vessels by a kind of radiation or straight-line trajectory in which 

 obstacles produce sharply-defined shadows. This' looks like a realisation of R. W. 

 Wood's " fourth state of matter," and suggests that neutral doublets of high velocity 

 come into action at high temperatures and low pressures. Whether these doublets are 

 identical with Wood's electronic doublets, or with Righi's "magnetic rays" (which 

 consist of positive atoms attended by revolving electrons) cannot at present be discussed. 



Shortest Sound Waves. Advances into" the region of shortest sound waves were 

 made almost simultaneously by Campbell and Dye 4 and by Lebedef and Neklepajef 5 

 in 1911. The former passed sparks of definite frequency close to the mouth of a Kundt's 

 dust tube. They were able to obtain as many as 50 streaks per cm, which means a 

 frequency in air of 830,000. The number agreed with the value deduced' from the 

 capacity and inductance of the spark circuit within 5 per cent. Lebedef calculated the 

 shortest observable sound waves from Stokes's formula governing the attenuation of 

 sound by the viscosity of the gas, introducing corrections made by Rirchhoff and 



1 Physikalishe Zeitschrift, 12, p. 976 (1911). 



* Deutschen Physikalischen Gesellschaft, Verhandlungen, 13, p. 482 (1911). 

 3 Ibid., 13, p. 1117 (1911). 4 Electrician, 66, p. 862 (1911). 



*Annalen der Physik, 35, pp. 171 and 175 (1911). 



