218 EVAPORATION AT LOW TEMPERATURES. 



very hard, so that we get about with as little diffi- 

 culty as if we were walking upon the bare ice. It is 

 pounded as hard as the drives in the Central Park. 



All these unusual phenomena are, as has been hith- 

 erto observed, doubtless due to the close proximity of 

 the open sea. How extensive this water may be is of 

 course unknown, but its limits cannot be very small 

 to produce such serious atmospheric disturbance. It 

 seems, indeed, as if we were in the very vortex of the 

 north winds. The poet has told us that the north 

 winds 



" Are cradled fur down in the depths that } r awn 

 Beneath the Polar Star ; " 



and it appears very much as if we had got into those 

 yawning depths, and had come not only to the place 

 where the winds are cradled, but where they are 

 born. 



. I have been making, all the winter through, a series 

 of experiments which give me some interesting re- 

 sults. They show that evaporation takes place at the 

 very lowest temperatures, and that precipitation often 

 occurs when the air is apparently quite clear. To 

 determine this latter, I have exposed a number of 

 smooth and carefullv measured ice-surfaces, and have 

 collected from them the light deposit. These accu- 

 mulations, after reducing them to the standard of 

 freshly fallen snow, amount thus far to seven eighths 

 of an inch. To determine the evaporation, I have 

 suspended in the open air a number of thin ice-plates, 

 made in a shallow dish, and some strips of wet flannel. 

 The flannel becomes perfectly dry in a few days, and 

 the ice-plates disappear slowly and steadily. I gen- 

 erally weigh them every second day, and it is curious 

 to watch my little circular disks silently melting away 



