ABOUT THE 20tH OF DECEMBER, 1836. 



159 



precipitated by it. Still, it seems probable that a part of this southerly wind 

 did continue on its course, and produce the snow which was observed to fall. 

 I infer that the current was mainly turned back upon itself, so that the moisture, 

 as fast as precipitated, fell through the lower current, still blowing from the 

 south-east. My idea may, perhaps, be best illustrated by a diagram. 



A part of the moisture of this south-east current might be frozen from the 

 cold of elevation, even if it were driven back in the direction from which it 

 came. But, falling through a warm stratum, before it reached the earth's sur- 

 face it would be entirely melted. At several stations hail fell in small quanti- 

 ties very soon after the wind changed. This might be owing to the moisture 

 of the warm current suddenly condensed by contact with the cold one, and 

 sustained by this upward motion, until the frozen drops had acquired the size 

 actually observed, which in no case was very great. 



Why more rain fell at some stations than at others only moderately distant 

 I cannot certainly say. The causes, doubtless, were local, and it would be 

 unsafe to assign particular reasons without a good knowledge of the localities. 

 Such an effect, however, might be produced by a hill of moderate elevation, 

 which would raise the lower current, and, consequently, the returning upper 

 current, to an unusual elevation, producing a corresponding depression of tem- 

 perature. 



The observations of the thermometer on pages 131 — 133 are believed to pre- 

 sent nothing very difficult of explanation. That the temperature should rise 

 under a southerly wind was to be anticipated. The wind blew from a southern 

 quarter more than twelve hours, in which time it probably travelled nearly five 

 hundred miles, or, making allowance for the obliquity of its course, between 

 four and five degrees of latitude. The difference of temperature corresponding 



