72 CLIMATE. 



above what frequently occurs even in the mildest parbs of 

 Europe. 



In stating the observed minimum at SS^, it must be re- 

 collected, that the observations were taken at a point raised 

 above the lake, and about half way up the hill bordering the 

 station on the south. 



In the valley below, from the combined effects of radia- 

 tion, evaporation, and the descent of the colder columns of 

 air by their superior weight, which are moreover compara- 

 tively undisturbed by the wind, the temperature frequently 

 falls below freezing point, and ice is often found in the dry 

 season half an inch thick. Hoar frost is commonly seen 

 extending half way up the hills on every side, disappearing 

 as the power of the sun's rays gradually increase. The 

 difference is most evident in descending into the lower 

 valleys on a dark clear and still night, when the sudden im- 

 mersion into the column of air next the ground, cooled by 

 its contact with the radiating earth at the bottom of the 

 valley, strikes one with a sudden chill. As a consequence of 

 the same cause, the lower valleys are frequently filled with a 

 dense fog, while the stratum of air immediately above is per- 

 fectly clear and transparent. 



So powerful is this effect of radiation from the earth, that 

 a cup of water or milk, placed on the ground, even in the 

 higher situations, instantly freezes, while a thermometer, 

 elevated three feet above it, will only indicate a temperature 

 of 38°, 39°, or 40°. This fact leads to some important con- 

 clusions, both as to the situation of houses, and of ground 

 selected for horticultural or agricultural purposes. In a clear 

 bright day, the thermometer generally attains its maximum 

 at about 2 or I- past 2 p. M., but this is, to the feelings, by 

 no means the hottest part of the day, owing to the constant 



