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XXI. Gas Theory §c. 



To the Editors of the Philosophical Magazine. 

 Gentlemen, 



REFERRING to a quotation on page 40 of your July 

 number concerning the difficulty of reconciling the 

 theoretical and actual ratios of specific heats or elasticities in 

 the case of a permanent gas with diatomic molecules, I have 

 long been accustomed to teach (I hope correctly) that any 

 rotational energy possessed by a dumbbell about its longi- 

 tudinal axis could have no influence on smooth collisions, and 

 accordingly could not be transferred or altered in amount ; 

 therefore such rotation ought not to be included in the par- 

 tition of energy within the meaning of the Maxwell-Boltzmann 

 law when properly stated. The wording of this law should 

 contain the phrase effective degrees of freedom ; and of these 

 there are manifestly 5 in a rigid dumbbell, thus giving at once 

 the theoretical and observed ratio 1*4. The question of vibra- 

 tional energy is different : that has to be, and to some extent 

 has been, dealt with in another manner. 



As I am writing may I take the opportunity of congra- 

 tulating Dr. H. A. Wilson on his successfully destructive 

 criticism, in the same July number, of the over emphasized 

 experiments of M. Oremieu, and of the revolutionary deduc- 

 tions too readily promulgated on the strength of them. 

 I am, Gentlemen, 



Your obedient Servant, 



Oliver Lodge. 



University of Birmingham, 

 July 13, 1901. 



XXII. Notices respecting New Books. 



Papers on Mechanical and Physical Subjects. By Osborne 

 Reynolds, F.B.S., Mem. Inst. C.E., LL.D., Professor of 

 Engineering in the Owens College, and Honorary Fellow of 

 Queen's College, Cambridge. Reprinted from various Transactions 

 and Journals. Vol.11. 1881-1900. Cambridge: at the University 

 Press, 1901. Pp. xii + 740. 



r PHE task of grappling successfully with the steadily increasing 

 -*- volume of scientific literature is a problem essentially modern, 

 a problem which did not trouble our forefathers in the seclusion 

 Phil. Mag. S. 6. Vol. 9. No. 8. Aug. 1901. R 



