Fitzgerald- -jE'/ec^nc and Thermal Phenomena. 441 



and in every direction at right r.ngles io this 



Pr P - p, 

 where 



P = -fTT (-^0 - ^v-^ [m^Vo + ^moVo - fmoVo + -^ {m^Va + 2wot?2 - m^v^) ] , 



and 



p = Utt (Vq - -^o) {w«2% + 2wo% - ma^'s} . 



If in this m-i and th he negative quantities, jo will he negative, 

 and the state of stress will he a pressure less than the average along 

 the line from which is measured, and an equal excess ahove the 

 average pressure in every direction at right angles to this ; and this 

 is the state of stress that Maxwell has shown will explain electro- 

 static forces. 



If we take the particular case of two parallel planes and sup- 

 pose P and p constant all the way across, as they evidently must 

 be, we have, supposing m^ = 0, that m-oVi? and moVoVo must he 

 constant as we go across, so that Vo and Vi must vary inversely 

 as the square root ®f ;wo; and if we suppose temperature defined 

 by the square of the velocity, i. e. by Vq we have that it must be 

 of the form To + T{)\ where To and T^ are constants and r the dis- 

 tance from one of the planes. 



In this method of describing electrostatic phenomena, what 

 Maxwell calls the electric displacement would be proportional to 

 the square root of p ; and what he describes as the polarisation of 

 the medium I would describe in the same words, and explain as a 

 distribution of the molecules and their velocities in which these 

 were not uniformly distributed in every direction. 



I have not propounded any hypothesis as to the nature of con- 

 duction, but it would evidently correspond to a transference of 

 entropy by means of heat engines which would produce heat cor- 

 responding to the resistance of the conductor, and also produce 

 magnetic phenomena in the neighbouring dielectric. I have not 

 propounded any hypothesis as to the nature of magnetic displace- 

 ments, but it seems probable that they might be Ulustrated by 

 introducing molecular rota tion. 



I am bringing forward his coEflmunication ao at all so much 

 for the sake of the hypothesis it coiitaiEB as for the sake of calling 



