332 



SCIENCE 



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



produced in the form of heat. It follows 

 from the energy principle that the quantity 

 of caloric generated in the process is such 

 that its total energy at the final tempera- 

 ture is equal to the work spent. If a quan- 

 tity of caloric represents so many neutral 

 molecules of electricity, one can not help 

 asking where they came from, and how they 

 were produced. It is certain that in most 

 cases of friction, wherever slip occurs, some 

 molecules are torn apart, and the work 

 spent is represented in the first instance by 

 the separation of electric ions. Some of 

 these ions are permanently separated as 

 frictional electricity, and can be made to 

 perform useful work; but the majority re- 

 combine before they can be effectively sepa- 

 rated, leaving only their equivalent in ther- 

 mal energy. The recombination of two ions 

 is generally regarded simply as reconsti- 

 tuting the original molecule at a high tem- 

 perature, but in the light of recent discov- 

 eries we may perhaps go a step further. 

 It is generallj'^ admitted that X or y rays 

 are produced by the sudden stoppage of a 

 charged corpuscle, and Lorentz, in his elec- 

 tron theory of radiation, has assumed that 

 such is the case however low the velocity of 

 the electron. A similar effect must occur 

 in the sudden stoppage of a pair of ions 

 rushing together under the influence of 

 their mutual attraction. Rays produced in 

 this way would be of an exceedingly soft or 

 absorbable character, but they would not 

 differ in kind from those produced by elec- 

 trons except that their energy, not exceed- 

 ing that of a pair of ions, would be too 

 small to produce ionization, so that they 

 could not be detected in the usual way. If 

 the X rays are corpuscular in their nature, 

 we can not logically deny the corpuscular 

 character even to the slowest moving rays. 

 We know that X rays continually produce 

 other X rays of lower velocity. The final 



stage is probably reached when the average 

 energy of an X corpuscle or molecule of 

 caloric is the same as that of a gas molecule 

 at the same temperature, and the number 

 of molecules of caloric generated is such 

 that their total energy is equal to the work 

 originally spent in friction. 



In this connection it is interesting to note 

 that Sir J. J. Thomson, in a recent paper 

 on "Ionization by Moving Particles," has 

 arrived, on other grounds, at the conclu- 

 sion that the character of the radiation 

 emitted during the recombination of the 

 ions will be a series of pulses, each pulse 

 containing the same amount of energy and 

 being of the same type as very soft X rays. 

 If the X rays are really corpuscular, these 

 definite units or quanta of energy generated 

 by the recombination of the ions bear a 

 close resemblance to the hypothetical mole- 

 cules of calorie. 



It may be objected that in many cases of 

 friction, such as internal or viscous friction 

 in a fluid, no electrification or ionization is 

 observable, and that the generation of cal- 

 oric can not in this case be attributed to the 

 recombination of ions. It must, however, 

 be remarked that the generation of a mole- 

 cule of caloric requires less energy than the 

 separation of two ions; that, just as the 

 separation of two ions corresponds with the 

 breaking of a chemical bond, so the genera- 

 tion of one or more molecules of caloric 

 may correspond with the rupture of a phys- 

 ical bond, such as the separation of a mole- 

 cule of vapor from a liquid or solid. The 

 assumption of a molecular constitution for 

 caloric follows almost of necessity from the 

 molecular theories of matter and electricity, 

 and is not inconsistent with any well-estab- 

 lished experimental facts. On the con- 

 trarj', the many relations which are known 

 to exist between the specific heats of similar 

 substances, and also between the latent 



