At a recent meeting of the American Society of Civil Engineers,
observations on the temperature of the earth, as shown by deep mines, were
presented by Messrs. Hamilton Smith, Jr., and Edward B Dorsey. Mr. Smith
said that the temperature of the earth varies very greatly at different
localities and in different geological formations. There are decided
exceptions to the general law that the temperature increased with the
depth. At the New Almaden quicksilver mine, in California, at a depth of
about 600 feet the temperature was very high--some 115 degrees; but in the
deepest part of the same mine, 1,800 feet below the surface and 500 feet
below sea level, the temperature is very pleasant, probably less than 80
degrees. At the Eureka mines, in California, the air 1,200 feet below the
surface appears nearly as cool as 100 feet below the surface. The normal
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
hottest are in trachyte and the "coal measures," namely, the Comstock
mines in trachyte and the South Balgray in the "coal measures." Mr. Dorsey
considered that experience showed that limestone was the coolest
formation.
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