1310 
En + (1 Ha)’ d 
ey. es ae me (| at 2a,,) d 
From: these values the variation of the energy may be found. 
Apparently now also the terms A/,* and B/, give parts which are 
quadratic in the quantities e (or a) and which therefore on the 
average do not drop off. After using the symmetry of the expression 
it is possible to put down the result as follows 
DAI" PERES 
However, another correction of the same nature will still 
be required. Above it was taken as a matter of course that 
the averages of first powers of e,...e, will be zero. Properly 
rb: : : Ou 
taken this is the case with the quantities LS aa On the other 
Mij 
hand one finds from the relations (11) 
Ehle + £4). 
This value should be taken into account if we take the mean 
value of the principal term of the tension Ax 
DAE A Bib se) 
therefore a correction is found to an amount of 
(4 +45)(,' — 27). 
Consequently on the whole,- to the thermical pressure we found 
before, 
we a 
3 1 
has to be added. 
It will be permitted to neglect.this term when the coéfficients 
C and D are large with respect to A and B. 
Of course it would be likewise possible to indicate the corre- 
sponding terms at the farther calculations of the equation of state 
which we have mentioned in this contribution. To indicate the 
principle it seemed to us to be sufficient to treat only the thermal 
pressure in this way. Further we must point out that if once these 
terms are neglected it will have no sense to make any difference 
between the density before and after the strain, when we 
calculate the energy for a unit of volume, or to take into account 
other differences of the same kind. Van Evurpincen has not always 
considered this (lc. pg. 22—23); in consequence of this there occur 
terms in his results that are of the same order as the other neglected 
‘terms, 
