220 The Heat of the Comstock Mines. [March, 
varying from half a minute to two minutes. The iron of 
the pipe is so thin and its conductivity so great that there is 
practically a slender current of air moving through a body 
of hotter air. 
The iron receives heat both by immersion in the hot air 
and by direCt radiation from the still hotter walls. The 
currents confined in it must be thrown against its sides by 
eddies, and the air is thus made to absorb heat by contact 
as well as by the transmission of heat-rays through it. 
Drifts that do not exceed 200 or 300 feet in length are 
usually not above no 0 or 112 0 F. in temperature, and more 
often they are below this. But when the length increases 
to 1200 and 1500 feet the temperature may rise to 116* F. 
without any other change in the circumstances. 
So far as the author’s personal experience goes, the latter 
temperature has not been exceeded in any drift into which 
a good current of air is blown. By a “ good current ” he 
means one of not less than 700 or 1000 cubic feet a 
minute. Still he has no hesitation in asserting his confi- 
dence in the higher temperatures which others have some- 
times obtained. The view which he takes of the phenomenon 
and its cause admits of such exceptional heat at particular 
points as a rational consequence of the forces at work. But 
he regards them as exceptional, and believes the average 
temperature of those drifts which are considered to be dis- 
tinctively “ hot ” is usually not above 108 0 to 112 0 F., though 
rising to 116 0 F., when they are very long. 
These limits are, however, not in the least degree true of 
the water which enters the drifts from the country rock, and* 
also from the lode rocks. That approaches more nearly 
150° F. The large body of water which has filled the Savage 
and Hale and Norcross mines for more than a year, and 
from which it is safe to say a million tons of water have 
been pumped within twelve months, gave a temperature of 
154 0 F. Even after being pumped to the surface through 
an iron pipe exposed, in the shaft of the Hale and Norcross, 
to a descending current of fresh air for more than 1000 feet, 
and then flowing for 100 or 200 feet through an open sluice 
in a drain-tunnel which discharges into a measuring-box, 
the water in this box was found to have a temperature of 
no less than 145 0 F. 
But the water varies in temperature in different parts of the 
lode, like the rock and the air. In the East cross-cut 
2000 feet level, of the Crown Point Mine, which is noted for 
its extreme heat, the water, after flowing for nearly 150 feet 
over the bottom of the drift, was found to have a tempera- 
