d 
g=w— 7 (UILEN ar RE ss (BH) 
da 
In order to determine vr, we observe in the first place that the 
work done, during the time df, by the force acting on a single 
electron is 
mX 8 dt 
and that, by the formula (1), the element 2/2 contains 
GS a6) dads 
electrons having their velocity-pomts within the element dà of the 
diagram of velocities. Taking together the forces acting on all these 
particles, we find for their work 
m X > dxdt. § f(S, 7,5) da , 
an expression that has yet to be integrated over the whole extent 
of the diagram. On account of (4), the result becomes 
mXv = dx dt, 
so that, by (36) 
miX 
=== — av. 
e 
Now, the value of Y may be taken from (21). Substituting 
. 
v= 
em 
and using at the same time (23), we find 
1 d log A d 1 e Z 
X= — -| — == 6 o o (Ge 
2h dx a du (;) ie mo ey 
0 a, 
mi{ 1 dlog A d (AN 1 39 
ne acs) |e a 
i= da. 
PKP 
The expression (22) may likewise be transformed by introducing 
into it the value (38), or, what amounts to the same thing, the 
value of 
so that 
if we put 
and 
2hAX a 
h a a 
Lv 
that may be drawn from (21). One finds in this way 
W—W.+W,, 
