20G PROF. O. REYNOLDS ON AN ELECTRICAL CORONA 



ing-wax on the ball, I rendered them definite and perma- 

 nent. As the pressure of air increased, the brush became 

 fitful, and finally ceased altogether. It was best when 

 there was about four inches of mercury in the gauge. 

 The phenomenon could be produced with different pres- 

 sures of air by making a corresponding variation in the 

 action of the coil ; and hence I assume that there is a 

 definite relation between the intensity of the charge in the 

 ball and the pressure of the air surrounding it, under which 

 the phenomena can occur. 



The appearance is very faint — so faint that it is difficult 

 to see it even when close to the ball ; and I find that it 

 takes some time before the eye can fully appreciate its 

 beauty. It was unfortunately so faint that Mr. Brothers 

 was unable to photograph it. The plate was exposed ten 

 minutes ; but there was not the slightest trace of any thing 

 on it. 



The annexed woodcut represents the apparatus employed, 

 except that the receiver was replaced by the globe described 

 above. The light round the ball gives a fair idea of the 

 momentary appearance ; and it is impossible to represent 

 more, as this flickers and changes so rapidly. 



This corona has the same special features as the solar 



corona : — 



1. The rifts and general radial appearance. 



2. The bending and crossing of rays. 



3. The self-luminosity. 



4. The changefulness and flickering. 



There is one point in which it differs from the solar 

 corona ; but this is no more than must be expected. The 

 shading off of the light in the solar corona is much more 

 rapid than that in its electrical analogue. If, however, the 

 pressure of the air could be made to vary so that it was 

 denser close to the ball, even this difference could be done 

 awav Avith. 



