3 o2 THE POPULAR SCIENCE MONTHLY. 



old books that relate to this matter are unfortunately filled with ex- 

 aggerations, and the lack of recent evidence prevents our extracting 

 from them the portion of truth they perhaps contain. Pontoppidan, 

 in his " Natural History of Norway," describes a cavity in the vicinity 

 of Frederickshall, in which the duration of the fall of a stone appeared 

 to be two minutes. Assuming, says Arago, that the stone fell clear, 

 without hitting and being retarded by projections in the walls of the 

 cavity, the total depth indicated by its two minutes' fall would be 

 over 4,000 metres, exceeding by 800 metres the height of the highest 

 mountain in the Pyrenees. But it would appear that the noise of the 

 stone's falling was heard for two minutes that it consequently rolled 

 and bounded from point to point ; and modern travelers have nothing 

 further to say of the famous Frederickshall hole. Another account, 

 of the legendary cavern of Dolsteen, in the Island of Herroe, Norway, 

 is likewise doubtful. According to a belief among the inhabitants, 

 this cavern extended to and under Scotland. It is told that, in 1750, 

 two priests ventured far into it and heard the rumbling of the sea 

 above them. Coming to the brink of a precipice, they threw over a 

 large stone, which was heard to fall a minute after. Without, how- 

 ever, attaching importance to accounts from such unreliable sources, 

 it may still be admitted that natural cavities exist which might be 

 made use of in exploring the deeper strata of the earth's crust. M. 

 Babinet, who cherished the idea of forming a society for digging a 

 deep hole for such purposes, thought the question had its industrial 

 side which ought not to be lost sight of. " This is no longer," he 

 somewhere says, "the time of Voltaire, who so bitterly berated Mau- 

 pertuis, whom he described as having wished to pierce the earth that 

 we might see our antipodes by leaning over the edge of the well of 

 this antagonist of the irascible king of literature. Nobody would to- 

 day deny the possibility of sinking the shafts of mines to a depth of 

 several thousand metres, when we have such choice of ground, dimen- 

 sions, and, above all, time. Let us suppose that we have reached a 

 depth of four kilometres only, and cleared a suitable space. If men 

 can not support the heat, machines, which are not so delicate, can. We 

 see ourselves in possession of a vast space, the walls of which are of 

 the temperatures of our ovens and stoves. Conducting thereto a 

 stream of water, it issues hotter than boiling water, and is a veritable 

 mine of heat, as truly so as are the precious coal-mines of England 

 and Belgium." It is a fact that the heat of the springs of Chaudes- 

 Aigues, which reaches 80, is made use of by the inhabitants for pur- 

 poses of cooking, heating their houses, washing, etc. By conduits of 

 wood, in all the streets of the village, reservoirs on the ground-floor of 

 each house are supplied, and these serve the purpose of heating-stoves 

 in cold weather, fires and chimneys being dispensed with. In sum- 

 mer, the inflow is stopped by little sluice-gates at the inlet of each 

 supply-pipe, the water then flowing to the brook at the border of the 



