4 
O. N. Rood on the Electric Spark. 219 
Art, XXII.—On the Study of the Electric Spark by the aid of Pho- 
tography ; by Prof. OapEN N. Roop, of Troy, N. Y. 
PHOTOGRAPHIC images of the electric spark between the car- 
bon electrodes of the voltaic pile were obtained on silver plates in 
November, 1840, by Prof. B. Silliman, Jr. and Dr. W. H. Goode, 
(see this Journal [1], xliii, 185). These observers remarked the 
greater actinic activity of the negative spark as compared with 
the light from the positive electrode, which I believe is the ear- 
liest recorded observation on this point. These authors also 
noticed a double concentric structure in the impression from the 
electric spark similar to that described in this paper. 
Photographs of the stratification and luminous discharges in 
Geisler’s tubes were obtained in the spring of 1860, by Prof. 
W. B. Rogers of Boston, operating with one of Ritchie’s coils. 
These results were communicated to the British Association at 
their Oxford meeting in June, 1860, (Report, &c., Abstracts, P 30.) 
imilar photographs were obtained by Gunther and Dove, 
and presented by the latter to the Prussian Academy, on the 
27th of May, 1861. A photographic camera was employed, _ 
and an exposure of from 3¢ to 6 minutes.* In the same num- 
ber of P oggendorff’s Journal, W. Feddersen, in a highly inter- 
esting article on the electric discharge from the Leyden jar, 
ales, that by means of a concave mirror silvered according to ~ 
Liebig’s process, he obtained fine Agrees 2 
been ob 
*xxii, No. 96, p. 408 
In all these cases the electric light was photo 
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yeral years ago. 
Method employed,—M. E. Becquerel showed epee sed Be 
that pa Tr coa . fh * 
. | ted with the bromid of silver 
light of t the siecttis spark ; the discharge of 4 battery of four 
* Pogg. Annalen, vol. exiii, No. vii. 
