Baron Humboldt on Temperature of Springs. 281 



molten eai'ths. All these matters owe their temperature, and 

 the nature of their chemical constitution, to the place of their 

 origin. The mean temperature of ordinary springs is lower 

 than that of the atmosphere where they appear, when the 

 water is derived from high levels ; their temperature increases 

 with the depth of the strata with which they come in con- 

 tact at their origin. The numerical law of this increase has 

 been stated above. The mixture of the waters, which come 

 from the mountain elevations, or from the depths of the 

 earth, renders the position of the isogeothermal lines, or 

 lines of equal internal heat of the earth, difficult of detemiina- 

 tion, when the conclusion has to be come to from the tempe- 

 rature of springs as they rise. So, at least, did I and my 

 friends find it in some experiments which we made in Nor- 

 thern Asia. The temperature of springs, which has been so 

 constant an object of physical investigation for the last half 

 century, depends, like the height of the line of perpetual 

 snow, on numerous and highly complex causes. It is a func- 

 tion of the temperature of the stratum in which they have 

 their origin, of the capacity for heat of the ground, and of the 

 quantity and temperature of the atmospheric or meteoric 

 water that falls ; which last, again, according to the mode of 

 its origin, differs in its temperature from that of the lower 

 strata of the atmosphere. 



Cold springs, as they are called, can only give the mean, 

 temperature of the air, if unmixed with water that is rising 

 from great depths, or that is descending from considerable 

 heights, and when they have flowed for a very long way under 

 the surface — in our latitudes from 40 to 60 feet, in the equi- 

 noctial zone, according to Boussingault, one foot. These 

 depths are those, in fact, of the stratum of rock in which, in 

 the temperate and torrid zone respectively, the point of in- 

 variable temperature begins, in which the hourly, diurnal, or 

 monthly variations in temperature of the air are no longer per- 

 ceived. 



Hot springs burst out of tlic most diversified mineral strata ; 

 the hottest of all the permanent springs Avhich have yet been 

 observed, and which I myself discovered, flow remote from all 



