Distribution of Energy in a System of Material Points. 299 



(all those possessing, however, nearly the same degree of pre- 

 cision), and decidedly better results with these than with amy 

 of the other existing simple methods. 



Considerable aid in eliminating errors of parallax in such 

 work is sometimes found by looking down upon the horizontal 

 thermometer through a vertical tube having a small hole at 

 each end. One of the cheap French microscopes with its 

 lenses removed, and inverted in its stand, answers this pur- 

 pose well. 



With such a device two calibrations of the above-described 

 thermometer with threads of 3 and 5 centim. respectively, each 

 with only one series of observations, and requiring not more 

 than one hour and a half each for completion, gave results 

 whose average difference from each other at nine points was 

 O01 millim., and the arithmetical sum of the extreme differ- 

 ences was 0-12 millim., a result of sufficient accuracy for any 

 class of work of which such an instrument is capable. 



For brief descriptions of methods of separating threads of 

 mercury for calibration, reference may be made to the paper 

 by Russell, and the text-book by Pickering, noted below. 

 These processes are in general use, and are safe and convenient. 



References upon Calibration of Closed Thermometer-Tubes. 



Bessel. Posts-. Ann. \i. p. 287 (1826). 



Rudberg. Posts. Ann. ix. pp. 3-53, 566: xxxvii. p. 376 (1836): xl. 



pp. 39, 562 (1837). 

 Kohlrauseh, 'Physical ^Measurements,' p. 59 (English translation). 

 Pickering, ' Physical Manipulation,' ii. p. 75 (1876). 

 Thiesen (Neumann's Meth.), Carl's Rep. xt. p. 285 (1879). 

 Russell (Neumann's Meth, transl. from Thiesen), Amer. Journ. Sci. 



xxi. p. 373 (1881). 

 Marek, Carl's Repertorium, xt. p. 300 (1879). (Solution by least 



squares.) 

 von Oettina-en, Inaug. Diss., Dorpat, 1865. (This I have been unable 



to obtain.— S. W. H.) 



XXXIY. On Boltzmann's Theorem on the average Distribu- 

 tion of Energy in a System of Material Points* '. 



To the Editors of the Philosophical Magazine and Journal. 

 GENTLEMEN, Graz, April 6, 1882. 



POSSIBLY you may feel disposed to have the accom- 

 panying notice of a paper of Maxwell's translated for 

 your valuable ' Philosophical Magazine.' So far as I know, 

 this excellent paper of Maxwell's has not been reprinted in 

 your Magazine ; it may not, therefore, be without interest to 

 your readers that some notice of it should appear, if onlv ns 



* Translated from Wiedemann's Beibllltter. 



