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X. 



ON ETHEE STKESS, GEAVITATIONAL AND ELECTROSTATICAL. 

 By FREDERICK PURSER, M.A. 



Read November 9. Ordered for rublication December 2, 1908. Published January 19, 1909. 



In his great epoch-making work on " Electricity and Magnetism," Maxwell, 

 in conformity with his general line of thought, which always looked for 

 action in a medium in place of action at a distance, proposed the problem 

 of accounting for the action of static electricity by strains in the ether. 



This problem he considered himself to have so far solved as to indicate 

 the general state of stress which must be postulated in the ether, leaving for 

 further discussion the state of strain which would produce this stress. 



Subsequently (Article on " Attraction," Encyclopaedia Brittanicct) he 

 endeavoured to account by a similar state of stress for the phenomena of 

 gravitation, the deduction of strain from stress being, however, as before, left 

 untouched. 



Unfortunately in both problems the state of stress assumed in the ether 

 was not one for which a system of strains could be found, assuming the 

 ether, either a homogeneous isotropic, or even a general Greeiiian eolotropic 

 medium. 



I propose in the present paper to show that the Maxwellian stress is 

 not necessary, but that the phenomena can be completely saved by a system 

 of stress deduced from a certain system of strains according to the laws of a 

 homogeneous isotropic medium. Eor this purpose it may be well to go a little 

 into the meaning and drift of the problem. We may, in fact, state it thus : — 

 Consider in an indefinite free ether certain specks, whether of matter or 

 free electricity, introduced. The effect of these will naturally be to produce 

 displacements of the ether around them. What then we have to do is to 

 assign certain forms of displacement, such that the surface tractions over 

 a very small cell shall produce a resultant force which shall vanish if the 

 cell contains no speck of gravitating matter in the one problem, or of free 

 electricity in the other, but in case such should be included shall be identical 

 with the gravitation force or electric force in either case on the speck. 



