398 Scientific Intelligence. 



less than 30 to more than 120 feet per degree; and 30 meters for 

 1° C. ( = 54-7 feet for 1° F.) is the commonly adopted rate in 

 Europe, while in England 50 feet is adopted by some and 60 or 

 more by others. He considers the conditions in (l) coal mines, 

 (2) other mines, and (3) artesian wells and bore-holes; and the 

 action in modifying temperature taking place in mines : through 

 (1) ventilation, (2) underground flows of water, (3) chemical 

 reactions, and (4) the working operations ; and, in artesian wells, 

 from (1) pressure of water on the thermometers, and (2) convec- 

 tion currents in the column of water. 



In the ventilation in coal pits the amount of air passing through 

 varies from 5000 to 150,000 cubic feet per minute, and has a large 

 cooling effect. It is generally greatest in the deepest mines. 

 The escape of gas from a blow-hole is also cooling, usually low- 

 ering the temperature 2° or 3° ; and in one case the temperature 

 of 74° F. existed in the coal at a depth of 1588 feet, and 62° F. 

 in a hole with a blower of gas at a depth of 1588 feet. The dis- 

 charge of water causes a loss of heat. On the other hand, a 

 crushing of the coal raises the temperature. There is also varia- 

 tion dependent on the form of the surface above, it rising under 

 hills and falling under valleys. For correct determinations from 

 coal mines, therefore, the height of the pit above the sea-level 

 should be known; the exact mean temperature of the place; the 

 depth, at each station, beneath the surface ; the temperature of 

 the air in circulation ; the length of exposure of face ; whether 

 there is discharge of gas or not ; the dip of the strata, and the 

 quantity of water discharged. 



Eliminating the more doubtful observations, the seven best — at 

 Boldon, North Seat on, South Hetton, Rosebridge, Wakefield, 

 Liege and Mons, — give a mean gradient of 49-^ feet for 1° F. 

 The bore-holes at Blythswood, South Balgray and Creuzot, give 

 a mean of 50*8 feet. 



In other mines, the loss of heat by ventilation is much less 

 than in coal mines and that from pumped water far more. In the 

 Gwennap district, where 550 acres were combined for drainage 

 purposes, above 20,000,000 gallons have been discharged in 

 twenty-four hours from a depth of 1200 feet; the water issues at 

 temperatures from 60° to 68° F., or more than 12° above the 

 mean of the climate, showing a large abstraction of heat from 

 the rocks through which the waters percolate. Again, surface 

 waters may enter and lower the temperature. The underground 

 currents sometimes raise and sometimes lower the temperature of 

 the rocks. Mr. Were Fox, in his many careful observations on 

 underground temperatures gave preference to the rocks, and Mr. 

 Henwood, an equally experienced observer, considered the springs 

 as giving surer results. The ten best of Mr. Henwood's observa- 

 tions, at depths from 800 to 2000 feet, give a mean of 42*4 feet 

 per 1° F. ; and the observations in eight mines, 1100 to 2100 

 feet deep, by Mr. Fox, give 43-6 feet per 1° F. The observations 

 in European mines Professor Prestwich regards as too uncertain 

 for use. 



