225 



Saint Louis, the spriug temperature only a little cooler than Washing- 

 ton, and the suiniuer and autumn temperature of Boston, 



Ever}^ one has perceived that the sensation of cold depends on many 

 other things besides the temperature. 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, for 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 130 and 150 degrees. This heat would be difficult to endure 

 if it were not for the same rarefied condition of tlie 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 for a blanket. This 

 marked diftereuce between sun and shade is the result of the lack of 

 aqueous vapor in the 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 a peculiar feature of this climate. 

 Without the sheltering influence of forests or mountain ranges on the 

 north, something of the fierce cold is felt here of the blizzards or 

 northers which, coming from the fields of ice and snow in the north, 

 sweep with such deadly power over the plains farther east. They come 

 suddenly, with little warning, chilling with their icy breath the soft, 

 balmy air that precedes them, and causing the mercury to drop 40 de- 

 grees in half an hour, and from 80 degrees at noon to zero at night. 

 But their violence soon carries them past, and the following day may be 

 as pleasant as before the blizzard came. The changes from cold to 

 heat are just as sudden and great, under the influence of the warm 

 west wind, which comes down from the mountain sides extremely dry 

 and electrical, driving the frost before it and absorbing the moisture of 

 the ground and air. Under its influence the thermometer has risen, by 

 actual observation, 40 degrees in thirty-five minutes, and after it had 

 l)assed the thermometer has fallen 30 degrees in five minutes, so suddenly 

 did its in fluence cease. This peculiar west wind will be discussed later. 

 24738— Bull 2 -15 



