536 Variation of Temperature between Spring and River Water. 



this mean temperature ; while, after it has flowed for some 

 distance, it becomes of the temperature of the atmosphere, 

 or, in summer, even warmer, owing to the action of the sun, 

 both directly, and reflected or radiated from its bottom. 

 Besides this equable temperature in the water itself, spring or 

 well water is usually covered ; and, even if exposed, if the well 

 is very deep, the water will not freeze, or at least very slightly; 

 for frost does not act with its full power, except where there 

 is a free circulation of air. In open ponds, wherever bushes 

 hang over the water, the ice is weak. Indigena's supposition, 

 that there are earthy particles in river water, which render 

 it more susceptible of cold than spring water, cannot be true ; 

 for then the relative temperatures would be the same in winter 

 and in summer, which is not the case; and, besides, there are 

 frequently more earthy particles in mineral springs, or even 

 common land springs, than in clear river water, provided 

 it has not been fouled by extraneous matter; for it has a 

 tendency to deposit the earthy particles which it holds in 

 suspension. 



It is evident, also, that the supposition of Mr. Carr (Vol.V. 

 p. 395.) relative to anchor frosts, that the stones at the bottom 

 acquire a greater degree of cold, or, to speak more correctly, 

 lose more heat, than the water, is erroneous. J. G. has given 

 the reasons at p.770. ; and the glaciers of Switzerland afford 

 us an example. When a stone is deposited on a glacier of 

 any considerable size, but not larger than 1ft. or 18 in. in 

 diameter, it becomes penetrated with the heat of the sun, 

 melts the ice below it, and sinks into the glacier. But this 

 effect does not cease, as might be supposed, when the stone 

 sinks beneath the water which it has formed : on the contrary, 

 it continues to absorb heat from the rays of the sun, to keep 

 the water above it liquid by its radiation, and to sink deeper 

 into the body of the glacier, until it gets down beyond the 

 reach of the sun's rays ; when the water of the well which it has 

 formed is no longer kept liquid, and the stone is buried in the 

 ice. In summer, however, the water is kept liquid ; and cir- 

 cular wells, formed in this manner, are of frequent occurrence 

 on the glaciers, sometimes, in the morning, covered by a thin 

 crust of ice. 



Thus, the stones at the bottom of streams must tend to 

 raise, rather than lower, this temperature. Is it possible that, 

 in the agitation of a stream at its bottom, if violent, momen- 

 tary and minute vacua may be formed, tending to increase 

 the intensity of the cold ? 

 Heme Hill, Sept. 2. 1836. 



