“LET us get back to our subject. At the bottom of mines, I told you, a high temperature prevails, which keeps up during the whole year. There is always the same heat, winter and summer. The deepest excavation miners have ever made is in Bohemia. It is inaccessible to-day. Landslides have partly filled it. At the depth of 1151 meters the thermometer indicated a perpetual heat of forty degrees, almost the temperature of the hottest regions in the world. And that, mind you, in winter as well as summer. When mountainous Bohemia was covered with ice and snow, it was only necessary to go down to the bottom of the mine to pass from the rigors of winter to the insupportable heat of a Senegal summer. One shivered with cold at the entrance and stifled with heat at the bottom.