54 PROF. O. REYNOLDS ON THE TAILS OF 



and the corona. It is quite clear that the tail of a comet 

 cannot be due to a discharge between two electrodes 

 situated on the comet itself. In the same way, from the 

 position occupied by the corona, it can hardly be due to 

 electricity passing between two electrodes on the sun. 

 In fact, if a comet's tail is electrical, it is due to a dis- 

 charge of electricity of one kind or another from the comet, 

 which for the time answers to one of the electrodes only. 

 The same may be said of the corona and the sun. If we 

 could observe the aurora from a point distant from the 

 earth, it is very probable that we should find the same to 

 be the case ; but whether this would be so or not, an as- 

 sumption has been made as to the cause and nature of the 

 aurora which will answer just as well for the corona and 

 comets' tails : it is, that the sun, acting by evaporation or 

 otherwise, causes continual electric disturbance between 

 the earth and its atmosphere, the solid earth being nega- 

 tively charged and the atmosphere positively, and that the 

 aurora is the reunion of these electricities taking place in 

 the atmosphere. 



Now, as has been already said, this assumption will 

 serve for the comets and the sun as well as for the aurora. 

 If there is a continual electric disturbance between the 

 sun and the medium in which it is placed, so that the sun 

 becomes negatively and the medium positively charged, the 

 reunion of these electricities would form the corona. It 

 must not be supposed that I assume the sun to be a reser- 

 voir of electricity which it is continually pouring into space. 

 I consider that the supply of electricity in the sun is kept 

 up by some physical action going on between the sun and 

 the medium of space, whereby the sun becomes negativeiy 

 charged, and the medium positively. 



This may be well illustrated by reference to the common 

 electrical machine : here the motion of the glass against 

 the rubber causes the glass to become positively and the 



