Again, there are some remarkable facts concerning the variation in the rate of increase in temperature with depth which seem equally irreconcilable with the theory that the heat in question is directly derived from a great, central, incandescent mass. M. Walferdin, by a series of careful observations in two shafts at Creuzot, proved that down to the depth of 1,800 feet the increase of temperature amounted to 1° Fahrenheit for every 55 feet of descent, but below the depth named, the rate of increase was as much as 1° Fahrenheit for every 44 feet. On the other hand, in the great boring of Grenelle at Paris, the increase in temperature down to the depth of 740 feet amounted to 1° Fahrenheit for every 50 feet of descent, but from 740 feet down to 1,600 feet, the rate of increase diminished to 1° for 75 feet of descent. The same remarkable fact was strikingly shown in the case of the deepest boring in the world--that of Sperenberg, near Berlin, which attained the great depth of 4,052 feet. In this case, the rate of increase in temperature for the first 1,900 feet, was 1° Fahrenheit for every 55 feet of descent, and for the next 2,000, it diminished to 1° Fahrenheit for every 62 feet of descent. In the deep well of Buda-Pesth there was actually found a decline in temperature below the depth of 3,000 feet. Perhaps the most interesting fact in connection with this question which has been discovered of late years, is that in districts which have recently been the seat of volcanic agencies, the rate of increase in temperature, as we go downwards in the earth's crust, is abnormally high. Thus at Monte Massi in Tuscany, the temperature was found to increase at the rate of 1° Fahrenheit for every 24 feet of descent. In Hungary several deep wells and borings have been made, which prove that a very rapid increase of temperature occurs. The deep boring at Buda-Pesth penetrates to a depth of 3,160 feet, and a temperature of 178° Fahrenheit has been observed near the bottom. The rate of increase of temperature in this boring was about 1° for every 23 feet of descent. In the mines opened in the great Comstock lode, in the western territories of the United States, an abnormally high temperature has been met with amounting in some cases to 157° Fahrenheit. Although this is the richest mineral-vein in the world, having yielded since 1859, when it was first discovered, 60,000,000_l._ worth of gold and silver, this rapid increase in temperature in going downwards threatens in the end to entirely baffle the enterprise of the miner. The rate of increase in temperature in the case of the Comstock mines has been estimated at 1° Fahrenheit for every 46 feet of descent, between 1,000 and 2,000 feet from the surface, but as much as 1° Fahrenheit for every 25 feet, at depths below 2,000 feet.