225 

Saint Louis, the spring temperature only a little cooler than Washing- 
ton, and the summer and autumn temperature of Boston, 
livery one has perceived that the sensation of cold depends on many 
other things besides the teyn perature. The dry and rarefied air of this 
altitude, allowing the rays of the sun to pass through with but trifling 
loss of heat, renders the lowest temperature much more endurable than 
it would be in moister climates. If the sun be shining and the air still, 
it matters little how low the thermometer may fall, and zero weather 
will be pleasant and agreeable. This warmth of the sun is not shown 
in the meteorological tables, tor the thermometers are set in the shade. 
By sun thermometers temperatures of 110 degrees and upwards are 
quite usual in winter, while 120 degrees has been observed in January. 
In the summer months the temperature in the sun usually ranges. be- 
tween 150 and 150 degrees. This heat would be difficult to endure 
if it were not for the same rarefied condition of the air which we have 
just found softening the effects of extreme cold. It gives a bracing, 
‘stimulating quality to the air in summer, and a fresh coolness to the 
‘slightest breeze, such as we never find in the low altitudes. Then, too, 
‘no matter how hot it may be in the sun, there is always a cool spot in 
the shade, and summer nights are rarely too warm fora blanket. This 
marked difference between sun and shade is the result of the lack of 
aqueous vapor in tbe air to become heated by the sun, for air of itself 
is diathermanous to the rays of the sun, letting them through without 
practically absorbing any of their heat. The great difference between 
day and night temperatures is shown in the large ranges of tempera- 
ture, being for the mean daily range 30 degrees, the mean monthly 
range 53,7 degrees, and the mean annual range 131 degrees. For com- 
parison, the same ranges of temperature at New Haven are, respect- 
ively, 16, 42, and 91 degrees. 
Sudden changes of temperature are 2 peculiar feature of this climate. 
Without the sheltering influence of forests or mountain ranges on the 
lorth, something of the fierce coid is felt here of the blizzards or 
horthers which, coming from the fields of ice and snow in the north, 
sweep with such deadly power over the plains farther east. They come 
uddenly, with little warning, chilling with their icy breath the soft, 
jalmy air that precedes them, and causing the mercury to drop 40 de- 
rees in half an hour, and from 80 degrees at noon to zero at night. 
ut their violence soon carries them past, and the following day may be 
s pleasant as before the blizzard came. The changes from cold to 
eat are just as sudden and great, under the influence of the warm 
est wind, which comes down from the mountain sides extremely dry 
nd electrical, driving the frost before it and absorbing the moisture of 
2e ground andair. Under its influence the thermometer has risen, by 
stual observation, 40 degrees in thirty-five minutes, and after it had 
ssed the thermometer has fallen 30 degrees in five minutes, so suddenly 
lits in fluence cease. This peculiar west wind wil! be discussed later. 
24738—Bull 2——15 
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