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fi 
Ken as of; 
EV 7 
and that the changes for fi, fa gis Jo, 4; and hg are independent 
of one another. 
This does not completely determine the condition: it is left un- 
settled, how the total region is spread over the unity of volume; 
whether it probably consists of comparatively few regions which are 
not so very small, or of a great many very small regions. In order 
to find something about this, we should have to calculate the pro- 
bable value of Ea . In the same way we might also try to find 
of, 
dt 
the suppositions which we have already made, new suppositions 
the probable value of ie Whereas [2] may be deduced from 
would be necessary, in order to find Ea It would be namely 
necessary, to make suppositions about the causes of change of 
lei). The significance of these quantities will appear from the 
following chapter. 
At first I had thought that the name “entropy of the ether” 
would be preferable to that of “entropy of radiation.” The name 
introduced by Wien ‘entropy of radiation,’ seems however, prefer- 
able to me. At the absolute zeropoint matter has an entropy — o. 
Now both the formulae, that of Wien and that of PLANCK, give for 
space without radiation 0 as the quantity of entropy; and this result 
seems correct to me. In order to maintain the analogy between the 
two kinds of entropy, it seems best to me, to ascribe the entropy 
not to the ether but to the radiation. A space, where no radiation 
takes place, can consequently not contain entropy of radiation. 
If we speak of entropy of the ether, it would probably have a 
orm like the following: 
rf F([Al) log F [df]. 
Probably however the entropy will be represented by a form like 
the following: 
fo (LAD F(LAI) too (@ F). [df] 
in which p represents the density, ie. it has the same function as 
n in the formula of BOLTZMANN: 
