98 WALKS AND TALKS. 



temperature is 87. As the mean surface temperature is 66, 

 and the depth of uniform temperature may be assumed at 50 

 feet, the increase is at the rate of 57 feet for one degree. At 

 Louisville, Kentucky, is an Artesian well 2,086 feet deep, 

 with a bottom temperature of 86 J. As the surface tempera- 

 ture is 55^, the rate of increase is one degree for every 66 

 feet. The Belcher well at St. Louis with a depth of 2,199 

 feet, has a bottom temperature of 73. 4. The surface tem- 

 perature being 55, the indicated rate of increase is one degree 

 for 116 feet. This is exceptional. At Columbus, Ohio, an 

 Artesian well 2,775J feet deep gives a bottom temperature of 

 91 with a surface mean of 52. This implies a rate of in- 

 crease of one degree for every 77 feet. Again, the well at 

 the Insane Asylum, St. Louis, is 3,843^ feet deep and affords 

 water at 105, giving a rate of increase of one degree for 

 76 feet. 



In deep mines, the temperature becomes intolerable, and 

 measures have to be adopted for the introduction of fresh air 

 from the surface. In the deep workings on the celebrated 

 " Comstock Lode," the temperature of the water at 2,000 feet 

 is 130. The water which filled the Savage and Hale and 

 Norcross mines for two years, had a temperature of 157. At 

 3,080 feet, the temperature is 170. To cool the air suffi- 

 ciently for the endurance of the miners, over thirty tons of 

 ice were consumed daily. [See further, Talk XXI.] 



Tunnels through mountains generally attain oppressive 

 temperatures. The Mont Cenis Tunnel through the Alps, 

 between Turin and Chambery, lies 4, 093 feet below the surface 

 of the Pass, or 5,251 feet below the summit of Mt. Frejus, 

 and is eight miles in length. The rise of temperature discov- 

 ered in the rocks is about fifty degrees. 



Assuming the rate of increase to be one degree for 60 feet 

 of descent, we should obtain, in the latitude of New York, 

 heat enough to boil water at a depth of about 9,000 feet. At 

 the depth of 50 miles, the temperature would be 4,600, 

 which is far above the melting temperature of ordinary min- 

 eral substances. In this method of reasoning we find an easy 



