334 



SCIENCE 



[N. S. Vol. XXXVI. No. 924 



reality there is no experimental foundation 

 for any other conclusion. According to the 

 usual gas formulae it would be possible to 

 extract an infinite quantity of caloric from 

 a finite quantity of gas by compressing it 

 at constant temperature. It is true that 

 (even if we assumed the law of gases to 

 hold up to infinite pressures, which is far 

 from being the case) the quantity of caloric 

 extracted would be of an infinitely low 

 order of infinity as compared with the pres- 

 sure required. But, as a matter of fact, 

 experiment indicates that the quantity ob- 

 tainable would be finite, although its exact 

 value can not be calculated owing to our 

 ignorance of the properties of gases at in- 

 finite pressures. In a similar way, if we 

 •assume that the specific heat as ordinarily 

 measured remains constant, or approaches a 

 finite limit at the absolute zero of tempera- 

 ture, we should arrive at the conclusion 

 that an infinite quantity of caloric would 

 be required to raise the temperature of a 

 finite body from 0° to 1° absolute. The 

 tendency of recent experimental work on 

 specific heats at low temperatures, by Til- 

 den, Nemst, Lindemann and others, is to 

 show, on the contrary, that the specific 

 heats of all substances tend to vanish as the 

 absolute zero is approached and that it is 

 the specific capacity for caloric which ap- 

 proaches a finite limit. The theory of the 

 variation of the specific heats of solids at 

 low temperatures is one of the most vital 

 problems in the theory of heat at the pres- 

 ent time, and is engaging the attention of 

 many active workers. Professor Linde- 

 mann, one of the leading exponents of this 

 work, has kindly consented to open a dis- 

 cussion on the siibject in our section. "We 

 are very fortunate to have succeeded in 

 securing so able an exponent, and shall 

 await his exposition with the greatest in- 

 terest. For the present I need only add 



that the obvious conclusion of the caloric 

 theory bids fair to be completely justified. 

 A most interesting question, which early 

 presented itself to Rumford and other in- 

 quirers into the caloric theory of heat, was 

 whether caloric possessed weight. While 

 a positive answer to this question would be 

 greatly in favor of a material theory, a 

 negative answer, such as that found by 

 Rumford, or quite recently by Professor 

 Poynting and Phillips, and by Mr. L. 

 Southerns working independently, would 

 not be conclusively against it. The latter 

 observers found that the change in weight, 

 if any, certainly did not exceed 1 in 10^ 

 per 1° C. If the mass of a molecule of 

 caloric were the same as that generally 

 attributed to an electron, the change of 

 weight, in the cases tested, should have 

 been of the order of 1 in 10' per 1° C, 

 and should not have escaped detection. It 

 is generally agreed, however, that the mass 

 of the electron is entirely electro-magnetic. 

 Any such statement virtually assumes a 

 particular distribution of the electricity in 

 a spherical electron of given size. But if 

 electricity itself really consists of electrons, 

 an argument of this type would appear to 

 be so perfectly circular that it is question- 

 able how much weight should be attached 

 to it. If the equivalent mass of an electron 

 in motion arises solely from the electro- 

 magnetic field produced by its motion, a 

 neutral corpuscle of caloric should not pos- 

 sess mass or energy of translation as a 

 whole, though it might still possess energy 

 of vibration or rotation of its separate 

 charges. For the purpose of mental im- 

 agery we might picture the electron as the 

 free or broken end of a vortex filament, and 

 the neutral corpuscle as a vortex ring pro- 

 duced when the positive and negative ends 

 are united; but a mental picture of this 

 kind does not carry us any further than the 



