14. EF. Loomis— Observations of the U. & Signal Service. 
These observations show considerable changes of tempera- 
ture at Denver, but they do not show the entire range of the 
thermometer, and they give no adequate idea of the sudden- 
ness of the changes. We perceive that between 11 Pp. M., Jan- 
uary 14th, and 7 a. M., January 15th, the thermometer at Den- 
ver rose 42°. We also perceive that the relative humidity fell 
from 71 to 21. The wind, which had previously blown from 
the northeast with a velocity of 8 miles per hour, at 9 P. M. 
(Denver time) veered suddenly to southwest with a velocity of 
12 miles per hour. These three circumstances, viz: the direc- 
tion of the wind, the dryness of the air and its high tempera- 
ture, prove beyond doubt that this air came from the west side 
of the Rocky Mountains. On the previous day the tempera- 
ture at Salt Lake City was 43°, and the relative humidity was 
50°. An area of low pressure passed over San Francisco, Jan- 
uary 14th about 4p. mM. During the following night the center 
passed near Salt Lake City, and at 4 p. M., January 15th, the 
center was near Leavenworth, having traveled about 1, 
miles in twenty-four hours. It was this storm which brought 
tion of the vapor. This warm and dry air supplanted the cold 
air which previously prevailed at Denver, and which still pre- 
vailed at neighboring stations east and north of Denver. A 
similar change, but of less magnitude, occurred at Cheyenne a 
little before the change at Denver, while at Dodge City and 
Omaha the change was still less, and at stations further north 
the change was scarcely appreciable. After the center of low 
ressure had passed Denver, the northeast wind returned and 
rought back the cold air which had constantly prevailed at 
stations not very distant. A similar change occurred at Chey- 
enne, nid aectnba at about the same hour. Thus we see that in 
winter, during periods of extreme cold on the east side of the 
Rocky Mountains, when the temperature at Denver sometimes 
sinks more than 20° below zero, there prevails in the Salt 
Lake Basin an average temperature of about 80°; and when by 
changes of atmospheric pressure this air is carried over the 
mountains it may reach Denver with a temperature of 50°, 
resulting from a precipitation of its vapor on the mountains. 
We then find a mass of air having a temperature of +50°in 
close proximity to a mass of air having a temperature of —20°, 
and by the movements of the atmosphere attending te 
of agreat storm these different masses of air may be brought 
