THE SWEDEN VALLEY ICE MINE 



287 



winter circulation 



spring of the year, as the snow on the hillside begins to melt and the 

 frost comes out of the ground, water naturally begins to trickle down 

 the sides of the shaft, where, strange as it may seem, it is frozen in the 

 form of small icicles. This freezing process continues, until by July 

 the sides of the pit are completely covered with a coating of ice a foot 

 or more in thickness. In the early fall the process stops and the forma- 

 tion of ice gradually melts. The sides of the shaft are of loose shale, 

 in which there are numerous crevices extending back and up into the 

 hill, the rock strata being rather 

 sharply inclined. A draught of 

 cold air, which at some places is 

 strong enough to extinguish the 

 flame of a small taper, issues from 

 these fissures in the summer time. 

 This draught is variable, being 

 stronger on hot than on cool days. 

 A heavy mist may also be seen 

 rising out of the pit and floating 

 off clown the hill close to the 

 ground. The temperature of the 

 pit during the past summer varied 

 between 25 and 32 degrees Fahren- 

 heit. 



The explanation of this phe- 

 nomenon appears to lie in the cold 

 currents of air issuing from the 

 crevices of the rocks along the 

 sides of the shaft. The air must wmmer circulaHm 



gain access to these fissures at some other point, which must be 

 at a higher altitude than that of the pit, as will be seen from the 

 following discussion. 



This being true, it is evident that in the winter time the column of 

 air directly over the pit is cooler and consequently heavier than that in 

 the rock passages. Therefore, it forces its way down into the pit and 

 up through the rock strata, chilling the rocks to a great depth and 

 storing up a vast quantity of " cold." We see, then, that the amount 

 of " cold " which is stored up, or the depth to which the rocks are chilled 

 at the beginning of warm weather in the spring, depends upon the 

 length and severity of the winter. 



As the warm weather comes on the column of air over the pit be- 

 comes heated and is displaced by the cold, heavy air flowing down out 

 of the passages. This cold current of air freezes any surface water 

 which flows over the edges of the pit and maintains a freezing tempera- 

 ture as long as the supply of " cold " in the hill lasts, after which the 

 circulation of air ceases and the ice formation melts. 



