38 



Ordinary Meeting, November 28th, 1871. 



J. P. Joule, D.C.L., LL.D., RR.S., Vice-President, in the 



Chair. 



Mr. Richard Samuel Dale, B.A., was elected an Ordinary- 

 Member of the Society. 



" Encke's Comet, and the Supposed Resisting Medium," 

 by Professor W. Stanley Jevons, M.A. 



The observed regular diminution of period of Encke's 

 comet is still, I believe, an unexplained phenomenon for 

 which it is necessary to invent a special hypothesis, a Deus 

 ex machina, in the shape of an imaginary resisting medium. 

 I cannot be sure that the suggestion I am about to make 

 has not already been made, but I have never happened to 

 meet with it ; and therefore I venture to point out how it 

 seems likely that the retardation of the comet may be recon- 

 ciled with known physical laws. 



It is asserted by Mr. R. A. Proctor, Professor Osborne 

 Reynolds, and possibly others, that comets owe many of 

 their peculiar phenomena to electric action. I need not 

 enter upon any conjectures as to the exact nature of the 

 electric disturbance, and I do not adopt any one theory of 

 cometary constitution more than another. I merely point 

 out that if the approach of a comet to the sun causes the 

 development of electricity arising from the comet's motion, 

 a certain resistance is at once accounted for. Wherever 

 there is an electric current some heat will be produced and 

 sooner or later radiated into space, so that the comet in each 

 revolution will lose a small portion of its total energy. In 

 the experiments of Arago, Joule, and Foucault the conver- 

 sion of mechanical energy into heat by the motion of a 

 Pkoceedings— Lit. & Phil. Soc— Yol. XI.— No. 4.— Session 1871-2 



