326 



NATURE 



[December 27, 1917 



not those usually accepted, nor will Fru Wiig of 

 Bossekop feel happy in appearing as " Mrs. 

 Wiggs. " " Gastivare " (p. 125) is neither Finn- 

 ish nor Swedish, and " kestikievari " would 

 seem to be the word intended. Mr. Butler, how- 

 ever, can drive reindeer, just as he can follow 

 game in Africa, and the main thing is that he 

 accommodates himself so skilfully to his sur- 

 roundings. Even if we cannot hope to follow him. 

 and may be content to view the wilds of Lapland 

 from Abisko or the top of Kiirunavaara, we feel 



statistical mechanics and their applications to the 

 problems of stellar dynamics. Since the positions 

 and motions of individual stars are known only 

 in a few instances, it is impossible to treat the 

 motions of stars by the ordinary methods of 

 classical mechanics, so that statistical methods 

 have to be adopted. Important investigations in 

 stellar dynamics have been made recently on this 

 basis by several investigators, more particularly 

 by Eddington and Jeans. There are two funda- 

 mentally different methods of treatment : (a) The 



ipp tent and sledge at Jukasjarvi. From " Through Lapland.' 



IPhoto F. H. Butler. 



something, as we turn his pages, of the dry, 

 healthy air and the crispness of the arctic snow. 

 Grenville a. J. Cole. 



STELLAR DYNAMICS AND STATISTICAL 

 MECHANICS.^ 



THE five papers referred to below do not form 

 a logical sequence of discussion, but are re- 

 lated to one another in that they are all more or 

 less directly concerned with the methods of 



1 (i) "Statistical Mechanics, based on the Law of Newton," Lund 

 Meddelande, Ser. ii.. No. i6. (2) " Ueber den Satz von den Gleichen 

 Verteilung der Energie," Lund Medd., Ser. i.. No. 79; Arkiv for Mat. 

 Astr. och Fysik, Bd. xii.. No. 18. (3) " Ueber hydrodynamisches Gleich- 

 gewicht in Sx^rnsystcmcn," Lund Medd., Ser. i., No. 82; Arkiv for Mat., 

 etc., Bd. xii., No. 21. (4) "Conceptions Monistique et Dualistique de 

 rUnivers Stellaire," Lund Medd., Ser. i., No. 81 ; Scientia, vol. xxii., 

 p. 77 (1917). (5) " Eine Studie uber die Analyse der Sternbewegungen," 

 Lund Medd., Ser. i., No. 78 ; Arkiv /dr Mat., etc., Bd. xii.. No. 10. All 

 by Prof. C. V. L. Charlier. 



Stars may be compared with the molecules of a 

 gas, and the effect of the various encounters con- 

 sidered, the discussion proceeding along the lines 

 of gas theory, (b) It may be supposed that the 

 encounters of stars have but small effect, so that 

 the stars may be regarded as describing orbits 

 under the general attraction of the stellar system 

 as a whole, the discussion then proceeding along 

 the lines of hydrodynamics. Both methods may 

 be expected to give results of value for the general 

 theory. 



Prof. Charlier has adopted the first of these two 

 methods in (i), and has worked out a kinetic 

 theory for the stars based upon Newton's inverse 

 square law of attraction ; in- gas theory the treat- 

 ment has usually supposed either that the mole- 

 cules are elastic spheres or that they repel each 

 other inversely as the fifth power of the distance. 



NO. 2513, VOL. 100] 



