Kupffer compared results obtained from the silver mines in Mexico, Peru and Freiburg, from the salt wells of Saxony, and from the copper mines in the Caucasus, together with an examination of the tin mines of Cornwall and the coal mines in the north of England, and found the average to be at least one degree of Fahrenheit for every thirty-seven English feet. Cordier, on the contrary, considers this amount somewhat overstated and reduces the general average to one degree Centigrade for every twenty-five metres, or about one degree of Fahrenheit for every forty-five feet English measure. _Thirdly._ That the lavas taken from all parts of the world, when subjected to chemical analysis, indicate that they all proceed from a common source; and _Fourthly._ On no other hypothesis can we account for the change of climate indicated by fossils. The rate of increase of heat in the Dudzeele shaft was no less than one degree Fahrenheit for every thirty feet English measure. At the time of recommencing sinking in the shaft on the 10th of April, 1849, the perpendicular depth was twenty-three hundred and seventy feet, the thermometer marking forty-eight degrees Fahrenheit at the surface; this would give the enormous heat of one hundred and twenty-seven degrees Fahrenheit at the bottom of the mine. Of course, without ventilation no human being could long survive in such an atmosphere, and the first operations of the commission were directed to remedy this inconvenience. The report then proceeds to give the details of a very successful contrivance for forcing air into the shaft at the greatest depths, only a portion of which do we deem it important to quote, as follows: