1 
tB 
me ese ae 2 
5 ( el oa dt le 
ie 
tB 
oe ade 
+ Aa { dt A . . . . . ° . . . (9) 
la 
Supposition A: The change I is a mechanical motion belonging 
to the values of the parameters (a). Therefore: 
Er eur w 
ah ig Cie EN es 
so that 
4 ‘eg me EN ge ST eee (2) 
da ; 
where (-A) is the external force, which at every moment must act 
on the system according to the parameter a, in order that « remains 
constant. Then also the total energy of the system 
He hig BIT Se Ls Sa iy) 
remains constant during the motion (a is kept constant, so that 
during the motion no work is done on the system!) We thus obtain 
l 
7B a : 
A | dt (T — 6) = — E.A(tg—ta) + (tp-- ta) A La) 
t 
A \ 4 (A) 
im = prab O9B— = pha Ognas | 
where A is the mean with ee to the time of the force A for 
the interval ¢4, tp. 
Supposition B. The change II is also a mechanical motion and 
belongs to the parameter values a + Aa. Then 7’+ ®= F# has 
also for this second motion a value “+ AL, which does not change 
with the time. Therefore 
“B 
I dt (T-+®) = AEB —t4)) = (te — ta) AE + EAQp—ta) @ 
A 
38 
Proceedings Royal Acad. Amsterdam. Vol. XIX, 
