temperature of the earth at a depth of 50 or 60 feet is probably near the
mean annual temperature of the air at the particular place. At the
Comstock mines, some years since, the miners could remain but a few
moments at a time, on account of the heat. Ice water was given them as an
experiment; it produced no ill effects, but the men worked to much better
advantage; and since that time, ice water is furnished in all these mines,
and drunk with apparently no bad results.

Mr. E.B. Dorsey said that the mines on the Comstock vein, Nevada, were
exceptionally hot. At depths of from 1,500 to 2,000 feet, the thermometer
placed in a freshly drilled hole will show 130 degrees. Very large bodies
of water have run for years at 155 degrees, and smaller bodies at 170
degrees. The temperature of the air is kept down to 110 degrees by forcing
in fresh air cooled over ice.

Captain Wheeler, U.S. Engineers, estimated the heat extracted annually
from the Comstock by means of the water pumped out and cold air forced in,
as equal to that generated by the combustion of 55,560 tons of anthracite
coal or 97,700 cords of wood. Observations were then given upon
temperature at every 100 feet in the Forman shaft of the Overman mine,
running from 53 degrees at a depth of 100 feet to 121.2 degrees at a
depth of 2,300 feet. The temperature increased:

100 to 1,000 feet deep, increase 1 degree in 29 feet.
100 to 1,800 feet deep, increase 1 degree in 30.5 feet.
100 to 2,300 feet deep, increase 1 degree in 32.3 feet.

A table was presented giving the temperatures of a large number of deep
mines, tunnels, and artesian wells. The two coolest mines or tunnels are
in limestone, namely, Chanarcillo mines and Mont Cenis tunnel; and the two