61 
0° and 382° F. would be of suitable volatility. Such a 
liquid avoids on the one hand the inconveniently large eyap- 
orating surface, and on the other the excessive pressure. 
Attention was called to the fact that the chart of curves, 
besides illustrating the subject of the paper, also was a com- 
pact substitute for the ordinary tables of tension, and repre- 
senting in a very clear manner, some of the laws pertaining 
to saturated vapors. For example, a simple inspection 
teaches that the tensions increase more rapidly than the tem- 
peratures, and on comparing the different curves, it appears 
that the rate of increase is greater for the liquids of lowest 
boiling points, and that there may be some exact relation 
between volatility and the rate of increase of tension. 
October 17, 1870. 
The President in the Chair. ‘Twelve persons present. 
Mr. R. Dinwippie exhibited specimens of crystallized 
Green Colored Feldspar from what is known as the Sea Wall 
of Mount Desert Island, Maine, where it occurs not very 
commonly in scattered particles or cavities. Many of the 
crystals were remarkably perfect and appear upon superficial 
examination to be peculiar. The color in most of them is 
very bright; often light but brilliant, and frequently not 
extending throughout the crystal. 
Pror. D. S. Martin exhibited a series of very fine speci- 
mens of Magnetite from Cornwall, Penn., constituting the 
“Codorus Ore” alluded to at the last meeting. Magnetite is 
pervaded with Cobaltiferous Iron Pyrites and has associated 
with and often encrusting it masses of Brochantite, essentially 
a Silicate of Copper, containing sometimes, a little Zinc and 
Lead. Also there was present on some of the specimens 
incrustations of Allophane. 
PROC. LYC. NAT. HIST. N. Y.—VOL. L. 5 
