218 The Heat of the Comstock Mines. [March 
source of heat be placed at H, a slow rotation in the direc- 
tion shown is maintained. 
To ensure success the disk must be sufficiently thin as to 
prevent its acquiring a uniform temperature. If the source 
of heat be at the same time applied at diametrically oppo- 
site portions of the disk, as at H and D, adjacent to the 
poles, the same effect will be produced. Since the amount 
of heat expended in producing motion of the disk is so 
enormous when compared with the force developed, it will 
be readily understood that this motor is of no value as such, 
but must be regarded as an interesting example of the inter- 
convertibility of force . — Journal of the Franklin Institute. 
III. THE HEAT OF THE COMSTOCK MINES.* 
By Prof. John A. Church, E.M., Columbus, Ohio. 
NE of the most striking phenomena connected with 
the mines on the Comstock lode is the extreme heat 
encountered in the lower levels. This heat proceeds 
from the rock, which maintains constantly a temperature 
very much higher than the average of the atmosphere in 
Nevada. 
The heat of these mines is a matter of more than usual 
interest, for they are the only hot ones now worked in the 
United States, and both in the present temperature encoun- 
tered and in the increase which is to be expected as greater 
depths are reached, they appear to surpass any foreign mines 
of which we have a record. 
The rock in the lower levels of the Comstock mines ap- 
pears to have a pretty uniform temperature of 130° F. 
The low conductivity of minerals to heat forbids the sup- 
position that a rock of 130° F. temperature can lose heat 
* Abstract of a Paper read at the Chattanooga Meeting of the American 
Institute of Mining Engineers, May, 1878, by permission of Lieut. Geo. M. 
Wheeler, Corps of Engineers, U.S.A., in charge of U.S. Geographical and 
Geological Surveys, west of the 100th meridian. 
