674 
T (Yen (t,) Yeh (t,)) 
ryt oT" 
CS ee — EE, ae Sr th —d t 3 
SE dy (t,) + = a va (ts) 
and this must be identified with (2); this theo 
OT Nes 
Òya (t,) hi 
on 
Oya (t,) == = [Oct frs ¥ rs (ts) + Whjrs (tats) Yrs(t,) Ay] 
Among the various conditions of integrability there must also 
occur: 
drin gl ON 
Oyeh(t,) Òyrs (£,)  Òrra (ts) Oyen (&) 
We get on the lefthand side: 
00 
OYrs (t,) 
=) 
On the righthand side: 
a ar’ a 
t,) Hy Ty = LOnsirs Yrs (ts Wrs'rs (to) X Yrslt) h‚] = 
OYA (t‚) Òyrs(t.) OVA (t‚) rs | y ( yet ( ) Y ( " 
= rap Let, 
Hence W „sen (t,t,) must be =O. Likewise all the y’s must drop 
out. We can also prove that in (3), where also the y‚ (¢,) appear 
as new independent variables Wijjs (¢;¢,) as well as Wijyrs (l‚t,) must 
drop out. All the yw’s must vanish. At the limit we get that Wij, (fr) 
must drop out, in other words: | 
The equation (J), in which the w’s do not drop out, can never 
be taken as the limit of a total differential equation Hence there is 
not to be found here a function of the present and earlier defor- 
mations, which acts as potential energy. 
Utrecht, June 1920. Institute for Theoretical Physics. 
