a) nee 
O. N. Rood on the Electric Spark. 295 
Form of the negative spark when drawn from the prime conductor 
by a short metallic rod. 
forms, the diameter of the positive figure is to that of the nega- 
tiveas2‘77istol. The same physicist has lately made an elab- 
orate examination of Priestly’s rings, which are formed when a 
large number of sparks strike on polished plates of metal, and 
arrived at the conclusion that the set of rings generated by neg- 
ative electricity is quite different from that produced by positive.* 
It conse uently becomes very interesting to ascertain whether 
coer terence also prevails between the photographs of the two 
sparks, 
~ 
The apparatus was arranged as before and sparks of negative 
electricity fell on the sensitive surface. 
i 
———————— 
Distance of 4, of inch. Round discs showing by their shading indica- 
tons of internal structure. Fig. 4 .1. 
3s Similar to above. 
Dises broken up into a number of small circles. See .3. 
Yo See diagram .4. 
Yo: The same as above ; sometimes the form at A is produced. 
Yo No spark passes over: the partial discharges produce no — 
but merely a general blackening of the plate under “i 
veloper, 
. Annalen, vol. exiv, No. 10, p. 193. 
AX Touz, Scl.—Secoxp Sexes, Vou. XXXII, No. 98.—Maxcu, 1862. 
29 
