52 PROF. O. REYNOLDS ON THE TAILS OF 



light from the heads of two small comets indicated carbon, 

 whereas that from the tails only gave a faint continuous 

 spectrum. For an electric discharge would first illuminate 

 the atmosphere of the comet, or even carry some of the 

 solid material off in a state of vapour, and then pass off to 

 the surrounding medium; thus, while the spectrum from 

 the head would be that of cometary matter, the tail would 

 be due to the incandescent ether. 



I would here suggest that gas, when rendered incan- 

 descent by electricity, may reflect light ; (it will certainly 

 cast a shadow from the electric light ;) and if this be the 

 case, part of the light from comets' tails may after all be 

 reflected sunlight. 



At any rate, it is certain that the appearance of streamers, 

 the rapidity of change and emission, the perfect trans- 

 parency, and the wave-like fluctuations which belong to 

 these phenomena are all exhibited by the electric brush ; 

 in fact the electric brush will explain all these appearances, 

 which have defied all attempts at explanation on a material 

 hypothesis. 



I have only to add that the main assumption involved 

 in the electric theory is, that space is occupied by matter 

 having similar electrical properties to those of gas ; and 

 I would ask, is it not more rational to make such an as- 

 sumption than it is to attribute unknown and inconceivable 

 properties to cometary matter ? 



Theories, even, if founded only on rational speculation, 

 often, I believe, prove very useful, inasmuch as they 

 afford observers a definite purpose in their speculations — 

 something to look for, something to establish or to refute ; 

 and I publish these speculations of mine at this particular 

 moment in the hope that they may perchance serve such 

 a purpose. 



