50 PROF. O. REYNOLDS ON THE TAILS OF 



naturally result from such a state of change and variation 

 in condition ? 



A. de la Rive remarks, " Electricity is one of the most 

 frequent forms which the forces of nature assume in their 

 transformations." It certainly often accompanies a change 

 in temperature. There is every indication that it is so in 

 our atmosphere ; for the times when its intensity is a max- 

 imum are just after sunrise and just after sunset, both 

 winter and summer. 



For these reasons it seems to me not only possible but 

 probable that these strange visitors to our system are 

 clothed in electrical garments with which the regular in- 

 habitants are unacquainted. 



The electricity must after all depend on the composition 

 of the comet ; for known substances do not all show the 

 same electrical properties. Hence, by assuming comets to 

 be composed of various materials, we. have a source to 

 which we can attribute the different appearances presented 

 by the different individuals. To the same source we may 

 attribute the irregularity in the direction of their tails, and 

 the lateral streamers they occasionally send out. 



Secondly, I think this electrical hypothesis is supported 

 by the, to me, seeming analogy between comets, the corona, 

 and the aurora — an analogy which suggests that they must 

 all be due to the same cause. They may be all described as 

 streams of light or streamers, having their starting point 

 more or less undefined, and traversing spaces of such ex- 

 tent and with such velocities as entirely to preclude the 

 possibility of their being material in any sense of that 

 word with which we are acquainted. 



The aurora has long been considered an electric phe- 

 nomenon ; and recently the same effect has been produced 

 by the discharge of electricity of very great intensity 

 through a very rare gas, there being no limit to the space 

 which it will thus traverse. This being so, why should 



