750 



B;i rnx ( — ij) ' 



ƒ■■ 



y COS Ydy = i[.rn^r]f^''''^-'^^=i il 



S' 



{\-z^rdz, = -h 



_ü- 



11= ^J^n-'ö'ma . . ' (5g) 



' 15 ' 



III the calculation of tlie niuTil)er of collisions we have, however, 



lip to now disregarded tlie influence of the inutnal attraction of the 



molecules and of their diuiension in the direction of I he velocity. 



If for this we introduce the usual corrections, we tind : 



ti = n- rt' )na e /?'/' (5) 



15 V — b 



in which t re|1resents the difference between the amount of potential 



energy thai the molecules in the li(jiiid possess on an average, and 



the amount which the}' possess at the moment of a collision. 



(7. Jagkr ') and M. Biuu-oriN ") had already derived expressions 



for the friction of liquids; JXciER considers exclusively "friction in 



consequence of impact forces", whereas BkilloiIxN takes besides these 



also the friction by means of Iranspoit into consideration. The 



method of calculalion differs somewhat from that followed above. 



The results at which they arrive, are in somewhat modified notation: 



JaOER ïj = 



61 



ix: 



Brillouin?^ "-s9"M''^+^^^,77^ — A 

 ( 2(x/ Ö)] 



In this Q represents the density, .s- the mean velocity of the mole- 

 cules, and D the mean distance of a pair of adjacent molecules. 

 (( and p are two unknown constants, which will not differ much 

 from 1, and which have been introduced, because all kinds of 

 approximations have been introduced into the calculation, which 

 renders the numerical coefficients not entirely certain. The first 

 term of Brili.ouin's formula refers to transport, the second to impact 

 forces. If seems to me that Brii.louin should also have corrected the 

 first term for the "thickness" of the molecules. In his tram of 



1) G. JaGER, Wiener Sitzungsber. Gil, p. 25:5, Anno 1893. 



2) M- Brillouin, Leqons sur la Viscosité des I^iquides et des Gaz. Paris. Gauthier- 

 VlLLARS 1907. 



