338 



SCIENCE 



[N. S. Vol. L. No. 1293 



any purposes where great hardness and 

 strength are essential. 



Investigation of Gaseous Explosions. — 

 Brief reference must also be made — and it 

 will he gratifying to do so — to the impor- 

 tant work of one of the committees of the 

 British Association appointed in 1908, 

 under the chairmanship of the late Sir 

 "William Preeee, for the investigation of 

 gaseous explosions, with special reference 

 to temperature. The investigations of the 

 committee are contained in seven yearly re- 

 ports up to 1914. Of the very important 

 work of the committee I wish to refer to 

 one investigation in particular, which has 

 proved to he a guiding star to the de- 

 signers and manufacturers of iutemal-com- 

 bustion engines in this country. The mem- 

 bers of the committee more directly asso- 

 ciated with this particular investigation 

 were Sir Dugald Clerk, Professor Callen- 

 dar, and the late Professor Bertram Hop- 

 Mnson. 



The investigation showed that the in- 

 tensity of the heat radiated by the incan- 

 descent gases to the walls of the cylinder 

 of a gas-engine increases with the size of 

 the cylinder, the actual rate of this increase 

 beiag approximately proportional to the 

 square root of the depth of the radiating 

 incandescent gas; the intensity was also 

 shown to increase rapidly with the richness 

 of the gas. It suffices now to say that the 

 heat in a large cylinder with a rich ex- 

 plosive mixture is so intense that the metal 

 eventually cracks. The investigation shows 

 why this occurs, and by doing so has saved 

 enormous gums to the makers of gas- and 

 oil-engines in this country, and has led 

 them to avoid the large cylinder, so com- 

 mon in Germany before the war, in favor 

 of a multiplicity of smaller cylinders. 



Chaeles a. Parsons 



(To be continued) 



A QUESTION CONCERNING THE 

 NATURE OF VELOCITY 



Tolman's remarkable success in deriving by 

 means of his principle of similitude^ a large 

 mnnber of physical laws, laws which have also 

 been otherwise derived by the more natural 

 and usual method of experimentation and 

 measurement, ought to indicate that there is 

 probably something fundamentally right about 

 his method of procedure. His argument in- 

 volves two imiverses, while physics knows only 

 one — and the bearing of his conclusions upon 

 the single universe that we know is not alto- 

 gether apparent. When he further asks it to 

 be assumed that the velocity of light and the 

 charge of the electron shall be the same in 

 both tmiverses, his argument seems far re- 

 moved from the facts of the laboratory and its 

 relevance to the usual physics may be, and in- 

 deed has been, brought into serious question. 



But his argument may be developed without 

 any appeal to two universes. So developed it 

 has an important bearing upon the theories of 

 the nature of electricity and of the manner 

 of the propagation of light. Consider any 

 two observers in our present universe, each of 

 whom with a diilerent set of standards of 

 measurement makes experiments and deter- 

 mines laws. The laws determined by the two 

 observers will have the same algebraic form 

 and will differ only in the value of the con- 

 stants which they involve. Since all of the 

 measureable quantities of physics are defined 

 in terms of three fundamental and ultimately 

 undefined quantities, each observer will need 

 only three standards- in order that he may 



1 Tolman, Phys. Eev., 3, 244, 1914; 4, 145, 1914; 

 6, 219, 1915; 8, 8, 1916; 9, 237, 1917. Bueking- 

 ham, ihid., 4, 345, 1914. Nordstrom, FinsTca Vet- 

 ensTcaps Soc. Forh., 57, 1914-15; Afd. A. No. 22. 

 Ishiwara, Science Eeport of TohoTtu Imp. Univ., 5, 

 33, 1916. Ehrenfest-Afanassjewa, Phys. Eev., 3, 

 1, 1916. Bridgman, ibid., 8, 423, 1916. Karrer, 

 ibid., 9, 290, 1917. 



2 All seem agreed that length and time are 

 fundamental and undefinable. About the third 

 quantity, force or mass, or energy, as the case may 

 be, there seems to be considerable debate. The ar- 

 gument of the present paper is valid, whichever 

 one of them is favored. I have chosen force be- 



