PHYSICAL CLIMATE. 501 



Alt. in TVmu. 



Feet. Fahr. 



Spring of Utliberg, near Zurich - - 1,532 48-92 



Ditto of Rossbaden, at St. Gothard - - 7,016 38-30 



Springs of Cumanacoa - - 1,148 72*5 



Ditto of Montserratt, above Santa Fe de Begota - - 10,680 39 '9 



Ditto in the Mine of Hualgayoc, in Peru ... -11,759 53'24 



The interior temperature appears to increase as we approach the equator. 



. * Lat. Depth in Feet. Temp. 



Salt Mines at Wielicksa, in Poland - 50 320 50 



Joseph's Well, at Cairo, in Egypt - - 30 210 70 



Mines of Mexico - - 20 1650 74^ 



In equinoctial regions the heat of the earth at but a short distance below the surface, 

 and that of permanent springs, is nearly uniform at all seasons, and usually corresponds 

 to the mean annual temperature of the external air ; but beyond latitude 45 the mean 

 heat of springs and caves is generally above that of the atmosphere. At Errontekies, at 

 the parallel of 68 , the difference between the mean temperature of the earth and of 

 the air amounts to 7 '74. Humboldt accounts for this by referring to the thick stratum 

 of snow which covers the earth in high latitudes, and prevents the loss of heat during 

 the winter months, by radiation, and by the contact of cold winds. But we have 

 striking and sufficient evidence that the superficial shell of the globe is not only heated 

 by the solar impressions, but is raised to a temperature at some distance from the surface 

 above that of the ambient air, by the action of its own deep-seated fires. There is strong 

 reason to suppose that below the solid crust of the earth upon which we dwell, the next 

 contiguous matter is in a state of fusion, at a temperature higher than any that man can 

 produce by artificial means. Hence, omitting all reference to the active volcanoes, and 

 to thermal springs at all temperatures below that of boiling water, found in all parts of 

 the world, it is a well-known fact, that in descending into deep mines the temperature is 

 greatly above that of the mean of the exterior air, and increases progressively with the 

 depth. This was first remarked by Gensanne, about the year 1740, in the lead mines of 

 Giromagny, near Beport. Saussure afterwards observed the same fact in the salt mines 

 at Bex, in Switzerland ; but the attention of naturalists was not generally directed to the 

 temperature of the lower strata, till Humboldt had executed an extensive and interesting 

 series of experiments in the mines of Freyburg, in 1791. The best set of observations 

 we possess on the temperature of deep places, is that which has been uninterruptedly 

 continued for more than half a century in the caves under the observatory of Paris. In 

 1783 the Count de Cassini, in concert with Lavoisier, placed a very delicate thermometer 

 in one of these excavations, for the purpose of observing the curious phenomenon of an 

 invariable temperature, which had been noticed to exist in the same place, by the first 

 Cassini, in 1671, and by La Hire, in 1730. The thermometer is placed at the depth of 

 rather more than thirty yards under the surface, in a bed of fine sand, and has indicated 

 no change of temperature, or at least its oscillations have not exceeded the ^L of a cente- 

 simal degree. The constant temperature exceeds at that depth, by 2*1 6 of Fahrenheit's 

 scale, the mean temperature at the surface : and supposing a uniform increase at the same 

 rate, we should arrive at the temperature of boiling water at the depth of 2542 yards 

 under the city of Paris. We may quote a few other results of observation. In the coal 

 mines of the north of England the temperature is 70 at the depth of 800 or 900 feet, 

 when the air at the surface is only 48 or 49 ; and in the mines of Valenciana in 

 Mexico, it is 92 when the surface-air is at 60. The following are additional examples : 



In a copper mine at Dolcoath, in Cornwall, a thermometer was kept eighteen months 

 buried in the rock to the depth of a yard. The depth of the mine was 1377 feet. The 



KK 3 



