HELMHOLTZ IN BERLIN 



matter is everywhere bathed by ether and is permeated 

 by it. If the ponderable matter and the ether are in 

 close grip one with the other, one may reason from the 

 movements of the former to those of the latter. But 

 if we consider the spaces which are empty of ponder- 

 able bodies and filled with ether alone, then the 

 question arises, has the ether any inertia ? Again, 

 suppose ponderable bodies move in the ether, can the 

 latter get out of their way, or does it pass through 

 the ponderable bodies like water through a sieve, or 

 does the ether remain at rest or is it partly dragged 

 along by the ponderable bodies ? Helmholtz finds, 

 on the assumption that ether is an incompressible 

 frictionless fluid, having no inertia, that the electro- 

 magnetic law of Clerk Maxwell, experimentally 

 proved by Hertz, holds good, and explains all the 

 phenomena. He finally draws important conclusions 

 as to the character of the discontinuity at the 

 boundary of ether and ponderable matter, and the 

 manner in which the electrical and magnetic forces 

 originate. This paper was a fitting termination to 

 the labours of Helmholtz in the lofty region of 

 mathematical physics. 



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