HEAT. 717 



heat increases. The average rate is 1° F. for 60 feet of descent. At 

 the Artesian well of Grenelle, a temperature of 85° F. was obtained 

 at 2,000 feet, equivalent to 1° F. for every 60 feet. In Westphalia, 

 at Neusalzwerk, in a well 2,200 feet deep, the temperature at the bot- 

 tom was 91° F., or 1° F. for 50 feet of descent. At Pregny, near 

 Geneva, a depth of 680 feet gave 63° F. At Yakutsk, Siberia, Mag- 

 nus found a gain of 15° F. in descending 407 feet, equal to 1° F. for 

 27 feet. In Algiers, an increase of 1° in 42 feet has been observed ; 

 and iu the Sahara 1° in 32 feet. 



From the average, 1 foot in 60 feet, it follows that the flow of heat 

 from the earth's interior is sufficient " to raise the temperature of the 

 earth by about one sixtieth of a degree Fahrenheit per foot on de- 

 scending." 



The rate 1° F. for 60 feet of descent, in the latitude of New York, 

 would give heat enough to boil water at a depth of about 9,000 feet ; 

 and 3,000° F., at a depth of about 33 miles. But the ratio is not an 

 arithmetical one, because both of the greater conductivity of the earth 

 below (owing to greater density) and the increased pressure, and 

 hence the depth of fusion, supposing fusion a fact, much exceeds this 

 amount ; but how much, has not yet been determined. 



Doubts with regard to the observations on the increase of heat downward in borings, 

 and in shafts in mines, come from tlie facts that chemical action, as stated beyond; 

 and, prominently, the oxydation of pyrite and other sulphides is a source of heat ; and 

 this has always to be considered in such investigations. Besides, local sources of sub- 

 terranean heat may exist. At the Comstock lode, in Nevada, the temperature of the 

 mine in some parts, at a depth of 1,800 to 2,000 feet, is 130° to 157° F., and over thirty 

 tons of ice per day are expended in keeping the air cool enough for the endurance of 

 the miners. The heat here is probably of subterranean origin, as the region is one of 

 former igneous eruptions. 



(3.) The wide distribution of volcanoes over the globe affords evi- 

 dence of internal heat. Volcanoes, extinct or active, border the Pa- 

 cific, from Fuegia to Alaska ; through the Aleutian Archipelago to 

 Asia; down the Asiatic coast, through Kamtchatka, Japan, and the 

 Philippines, to New Guinea, New Hebrides, and New Zealand ; and 

 they constitute half of the islands of this ocean, and two of them, in 

 Hawaii, are nearly 14,000 feet high. This volcanic region is equal to a 

 whole hemisphere, and is therefore evidence of a wide distribution of 

 interior heat. Volcanoes occur also through Java and Sumatra ; in 

 central Asia, in the Thian-Shan Mountains ; about the Mediterranean 

 and Red Seas ; in western Asia, and southern, central, and southwest- 

 ern Europe ; in Iceland, and in the West Indies. 



The ejection of melted rock through fissures has taken place over 

 all the continents : in Nova Scotia, Canada, New England, New Jer- 

 sey, and the States south, the region of Lake Superior, the Rocky 



