368 O. N. Rood on the Electric Spark. 
zs in. Much like the last. 
#z in. Also much like fig. 18, or like fig. 10, the cireumfer- 
ence of the circle being a dark ring. 
7s and ;,in. Like fig. 12, except that the figure is 13. 
enclosed in a ring. 
7, in. Like fig. 13, the white ring being often sha- 
ded uniformly with the exterior ring. Using a point, 
figures similar to 12 are obtained, their outline being 
quite circular. These correspond with those ob- 
tained by frictional electricity. 
This is the limit of the negative spark ; and on separating the 
electrodes farther, the negative brush is obtained. This pro- 
uces, as with frictional electricity, only a general diffused 
blackening of the plate, which is, however, slight in intensity 
when compared to that obtained by machine electricity. 
Form of the figures produced by the “* Luminous Atmosphere.” 
the negative pole, 
es 5: his : 
of the so-called “ atmosphere’ 
woul 
those 
