1S 
Ke Electrographs of Coins taken in the dialectric of a 
condensor. 
6. Photograph of bottom of developing tray broken in a 
dark room, upon plates which had been exposed 
to ** Réntgen” rays. 
7. Radiographs of a Key taken at more than six feet from 
vacuum tube. 
17. Arc Lamp For PHOTOGRAPHY, Which operates under con- 
ditions of absolute steadiness for all photographic pur- 
poses. 
18. SCREEN FOR DIFFUSING LIGHT, assuming many different 
shapes by a touch. 
Nos. 17 and 18 exhibited by the International Lamp Co. 
GEOLOGY: 
i: 
IN CHARGE OF J. J. STEVENSON. 
I. Suite of Orrs, Rocks and PHoToGRaApus from Cripple 
Creek, Colorado. Exhibited by Prof. J. F. Kemp. 
The ore deposits are oftenest associated with dikes of 
phonolite or nepheline-basalt that penetrate the red gran- 
ite of the Pike’s Peak region, or a decomposed breccia of 
andesite. They also line in veins which fill more or less 
irregular fissures in the andesite breccia away from dikes. 
The ores are fresh or decomposed telluride of gold. 
This district was described before the Academy, Feb- 
ruary 7, 1896. 
2. Suite of Ores, Rocks and PHoroGrapus from the Bertha 
and Wythe Zinc mines, in southwest Virginia. Exhib- 
ited by Prof. J. F. Kemp. The Siluro-Cambrian lime- 
stone has been originally charged with zinc blende and 
pyrites at the Bertha mines, and with these and galena at 
the Wythe mines. It has decomposed, leaving a residual 
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