220 0. N. Rood on the Electric Spark. 
ual experiment confirmed this idea to a most surprising degree: 
when a single spark was allowed to fall on the sensitive surface, 
sharply defined image, full of delicate details, was proauct™ 
Tply _- sone etngmribls ta they 
negatives then furnished good prints on paper. Sometimes - 
small original images were accompanied by an irregular ae 
halo caused by the diffused light of the spark, but this for 
" most part was so faint as in no way to interfere with the d 
ness of their outline. 
The question naturally arises whether these delicate and beat 
tiful images are produced by the action of the light on the ny 
tive plate, or are owing to a decomposition of the silver salt by 
electrical agency, in other words whether these pictures are P of 
tographs or electrographs. That they are due to the action 
light the following experiments will render probable. tae 
(1.) Sparks were allowed to fall on sensitive plates and thelt 
form was observed by the aid of a lens of one inch focal Jength 
on developing the latent images they corresponded in shape with 
bserved. 
yes from 
(2.) A glass plate was coated with plain collodion, free path 
iodid or Geqoniel and allowed to remain five minutes in the 
of nitrate of silver: it was then removed, and single Jodion 
were allowed to fall on different portions of the wet col k 
surface : under the action of the developer the well knows sP™* 
images speared : 
, A-simple clean glass plate without any coating at all was placet 
pore nitrate bath for a few seconds; on its removal and W 
quite wet, sparks were discharged on different portions of 
* Pogg. Anni, vol, liv, p. 54. 
