eee 
cies tly Be ihe” ede bial Soa aeeiee aaa iar ache oars ie cige oi sei. 33 Sie Se a a eae 
it re 
Te saphgiecs : % 5 
F. H. Blake— Vanadinite in Arizona. 145 
rays. This is the quantity also measured in Siemens and 
Hansemann’s experiments. Bdérnstein on the other hand, who 
used no alum cell, measured the excess of light effect over the 
heat effect of both luminous and obscure radiations, so that if 
there is a true diminution of resistance caused by light, it 
ought to have appeared more strongly in the experiments 
which have been described. 
Taking all these things into consideration, it appears safe to 
say then that if light causes any diminution in the electrical 
resistance of metals, it probably does not exceed a few thou- 
sandths of one per cent. 
Art. XIX.— Vanadinite in Pinal County, Arizona; by 
RANCIS HAYES BLAKE. 
ries. These planes are very minute. I was unable to find 
planes between O and 7-2. 
Wulfenite is also found in this mine but not in very perfect 
crystals. 
Pinal, Pinal County, Arizona, June, 1884. 
¥ Am. Jour. Sci.—Tuirp Series, Vou. XXVIII. No. 164.—Ave@ust, 1884, 
10 
