a Ee aes 
; ae 
e 
Figures by the Electric Spark. 293 
The corresponding negative figure is seen in (7). The cen- 
tral star with wnrred Aves referred to above, is Beaded by 
a deeply depressed circle, which is bounded by a slightly ele- 
vated ring. The terminal wires evidently acted here as points, 
for the star was not obtained when the discharge took place 
m balls. 
The electrodes D and E (fig. 1) are adjusted at equal distances 
from the upper and lower surface of the plate. Upon connect- 
ing D with the prime-conductor the positive spark falls upon 
face of the platé. Development by the lamp, without oblitera- 
tion of one of the figures, being impossible, the plate may be 
65° C. i 
heated in an air-bath to about 60°- It is more conven- 
lent, however, to throw the discharge upon the plate when warm, 
the figures then appear at once ng plates of glass, or 
® point, the following experiment was made. One end of 
spark having been made to fall on the spot marked out by the 
nd the latent image and very oe it. After 12 hours, this 
©, on developing, gave a good figure. : 
From the St — which the figures are produced, it meen 
appear that they are due to the attractions and repulsions of the 
* Riess ro. An xix), that the areas of the surfaces occu 
= by + —— ee coal " ce Seedoped taster the same conditions, 
as 7:1, 
