382 Notices respecting New Books. 



Thus it appears that in addition to the circular orbits in 

 the cone = tan — x \/2, there are an infinite number of other 

 periodic orbits, and also that all these orbits are unstable, 

 results which appear to be subversive of the physical theory 

 suggested by Sir J. J. Thomson. 



Yours faithfully, 



Cambridge, July 4, 1910. J. it. JEANS. 



XXXVII. Notices respecting New Boohs. 



Bulletin of the Bureau of Standards. Vol. 6. No. 3. February 

 1910. Washington: Government Printing Office. 



HIS part contains three important papers on Kadiation : Selec- 

 tive Badiation from various solids, by W. W. Coblentz ; Lumi- 

 nous efficiency of the Firefly, by H. E. Ives and W. W. Coblentz ; 

 Luminosity and Temperature, by P. Gr. Nutting. The first is a 

 continuation of a detailed examination of the emission curves of 

 very various bodies and contains the curves. The second paper 

 gives the luminous efficiency of a glow-lamp as *43 per cent., while 

 that of a firefly is 96*5 per cent, (allowance being made for the 

 variation of visual sensibility with the wave-length). The third 

 paper discusses the connexion between luminosity and tempe- 

 rature, making use of the author's visibility function, 



T 



V=V exp.(-/c(\-X w ) 2 ). 



A fourth article is a theoretical and experimental study of the 

 Vibration Galvanometer by Prank Wenner; another deals with 

 an experimental study of the specific heat of some calcium chloride 

 solutions between —35° C. and +20° C. ; measured in part by a 

 continuous flow method and partly with the use of a Dewar vessel 

 containing the brine into which heat is admitted electrically. The 

 investigation was undertaken owing to the extensive use of calcium 

 chloride brine as a circulating medium in refrigerating plants. 



The last article is by E. Buckingham on the definition of an 

 ideal gas. To the present reviewer there is something nugatory 

 about all such discussions, it being somewhat arbitrary as to what 

 the criteria of ideality should be, as soon as we attempt anything 

 more scientific than the application of Boyle's and Charles' laws. 

 But Mr. Buckingham's article is well worth a detailed consideration 

 as it makes clear many things which are often treated very loosely 

 in discussions on this subject ; and though some of these matters 

 have been explained before, it does not appear to be unnecessary 

 to repeat them. 



