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resemblance they bear to an electric brush. But to the 
electric phenomenon I am about to describe it is no mere 
general resemblance, it is an actual likeness with every 
feature identical. 
Before describing the phenomenon I may be allowed to 
state how I came to notice it. It will be remembered that 
in a former communication to this Society I ascribed the 
phenomena of comets and the corona to a certain electrical 
condition of the sun. Well, the peculiar appearance of Mr. 
Brothers’ photograph induced me to try if a brass ball, 
brought into the condition I had ascribed to the sun, would 
give off a corona presenting this appearance. 
The phenomenon is produced by discharging electricity 
from a brass ball in a partially exhausted receiver. To do 
this there is no second pole used, the objects which surround 
the outside of the glass probably answering to this purpose. 
In order to produce the desired appearance a certain relation 
is necessary between the pressure of the air and the inten- 
sity of the discharge. It is produced best when the receiver 
is a glass globe insulated on a glass stand, the ball being 
supported in its middle by a rod coated with indiarubber, 
to prevent its discharging and spoiling the effect. It is only 
negative electricity that is discharged into the globe. What 
becomes of this electricity is not clear ; when a machine is 
used it probably distributes itself on the inside of the glass, 
and induces a corresponding charge on the outside. When 
the coil is used it must escape back for I have had it going 
for hours without any variation. 
There is great difficulty even when the apparatus is right 
in producing the corona; using a large coil I just exhausted 
the receiver till the pressure was equal to half an inch of 
