of (12), we may, without changing the sum Yq, include in it not 
only the points A, but likewise the points O. Now, if the vectors 
0, A,, 
Yq due to the points O, and A, will be 
. 
— | N q; tin do, 
a 
as may easily be inferred from (11). There are similar expressions 
OF Ae 2.3, On Ay are denoted byt, fs, Vy, the: part of 
for the parts of the sum corresponding to QO, and A,, O, and A,, 
etc. Hence, if we introduce for a single partiele the vector 
Weert sata leg tamed Gete (13) 
and if we put 
ema EC LN 
the final result will be 
= ay do . . . . . ° . e (15) 
In this formula, the vector 9 is to be considered as a function of 
the coordinates because the number N may gradually change from 
one point to another (this $, @) and the vector q may vary in a 
similar way. If now the surface o is taken physically infinitely 
small, though of so large dimensions that it may be divided into 
elements, each of which is large in comparison with molecular dimen- 
sions, the expression (15) may, by a known theorem, be replaced by 
SNe ayo the REENER eh) Set ot EO) 
S being the space within the surface . 
d. It has been assumed till now that the quantity q occurs only 
in a limited number of points within each particle. By indefinitely 
increasing this number /, we obtain the case of a quantity g con- 
tinuously distributed. We shall then write gdr instead of ¢, and 
replace the sums by integrals. The condition (12) becomes 
. 
faar=0 
which we shall suppose to be fulfilled for each separate particle, 
the vector q is now to be defined by the equation 
. 
gf AAE DEE on (17) 
and the sum +g, whose value we have calculated, becomes | q dt, 
a 
taken for the space enclosed bij 6. If we still understand by © the 
vector given by (14), the value of the integral for a physically infinitely 
small space will be 
