PROF. O. REYNOLDS ON COMETARY PHENOMENA. 201 



attracted. But, so far as I can see, the straight tails which 

 are so often seen, and sometimes in conjunction with the 

 curved ones, can only be explained in the manner de- 

 scribed in my previous paper before this Society (see 

 Memoir, Nov. 29, 1870, p. 44 of the present volume), as 

 an electric brush or discharge through space. 



As a probable cause of the electricity in the vapour of 

 the comet, I would suggest that the evaporation taking 

 place from the surface of the comet might cause a crust 

 to form there, through which the subsequent vapour would 

 have to force its way in the form of jets, which, like the 

 jets from Armstrong's hydro -electrical machine, might 

 issue charged with electricity, the solid being charged with 

 electricity of the opposite kind. If this were the case, the 

 vapour, as it formed an atmosphere round the nucleus, 

 would discharge some of its electricity back, and so cause 

 those portions of the atmosphere near the solid to be 

 self-luminous ; and, besides this, there might be other 

 discharges, between the clouds or outwards into the 

 medium of space, so as to illuminate a part of or the 

 whole atmosphere. 



On this hypothesis, if the electricity of the tail is charged 

 with electricity of one kind, say negative, the solid head 

 must leave the neighbourhood of the sun charged with 

 positive electricity, which, as it gets further from the sun, 

 and evaporation becomes feeble, will at length overpower 

 the negative and charge the atmosphere of the comet, 

 which would then be attracted by the sun instead of re- 

 pelled ; so that the tail, if it had one, would be towards the 

 sun ; or else, if by this time the comet had no atmosphere, 

 it would carry off its charge, and (unless it lost it en 

 voyage) on its next appearance it would be charged with 

 positive electricity, and the first vapour would probably be 

 attracted instead of repelled, and the first tail point towards 

 the sun. 



