For ten years Professor Agassiz took observations concerning a very deep mine in the United States called the Calumet and Hecla Mine. He and Professor Chamberlin, after examining all the observations very carefully, came to the conclusion that in going down from the earth's surface the temperature rose at a rate of about 1° of heat (Fahrenheit) for every 125 feet. At the North Garden Gully Mine, Bendigo, Australia, and at the New Chum Mine a temperature of 99° F. was reached at 3000 feet, and 107° at 3645 feet. The rate of increase of temperature was reckoned to be 1° of heat (Fahrenheit) for every 80 feet. This rate of 1° for 80 feet was also found at a South German mine, Maldon, as well as at a Ballarat mine, and at a mine near Port Jackson. In a French mine more than 3000 feet deep, at the collieries of Ronchamp, the rate of increase was as high as 1° in 50 feet. In the North Staffordshire mines Mr. Atkinson, H.M. Inspector of Mines, found the increase to be on the average 1° in 65 feet; whereas in the South Staffordshire Hamstead Colliery Mr. F. G. Meachem found that the increase was 1° F. for every 110 feet. The same rate was obtained at the Baggeridge Wood Colliery, South Staffordshire. In South Wales, in the neighbourhood of Rhondda and Aberdare, the rate is 1° for 95 feet; at Dowlais, in the Merthyr coalfield, it was 1° in 93 feet; at the Niddrie Collieries, near Edinburgh, the increase is at the rate of 1° in 99 feet. It will thus be seen that all over the world there is an increase of temperature at a rate which, on the average, is about 1° for every 100 feet. There are 5280 feet in a mile; therefore, if this rate of increasing temperature were maintained, at a depth of 100 miles the temperature would be perhaps 5000° F.; a temperature at which steel would melt and boil away into vapour. At a depth of 200 miles the heat would be greater than that of the surface of the sun.[2] [Footnote 2: According to the calculations made by the late Mr. W. E. Wilson, F.R.S., in Ireland, 5773° Centigrade above the lowest temperature which is possible in space, or about 10,500° F.]