241 
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 tempera- 
ture of about 30°; 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 vapor on the mountains. We thus find a mass.of air having a tem- 
perature of -+- 50° in close proximity to a mass having a temperature of —20°, and 
by the movements of the atmosphere attending the progress of a great storm these 
different masses of air may be brought successively over the same station, causing a 




















' change of temperature of 50° in a single hour.’ 
4 **The following tables present numerical accounts of these changes from the same 
authority) 
, Temperature and relative humidity, January, 1875. 
i 
J — j ne a : i ; 
Salt Lake. | Cheyenne. Denver. | Pike's North 
: | Peak. Platte. | 
| Hour _- = — 
Date. | (Washing- 4, sl & iene on ae | ies | 2 Aye ee i: 
itontime).; 6g | Pela. |/ PH la. | ee ia pe | & eS 
Se isa]/ ao lsc] Bolsa | Po | ae8 | 2s /|s6 
BS) SE| 82 /s6| 88 (s8| 82/38/88) 28 
| a iSele eela las la |ee\& | az 
ane ne ee | 
| o NET. chy 98 “\Proct.| ° |Pr.ct.| ©. |Pr.ct| ° (Pr. ct 
| January 14..... 7.35 | 34 | —11 76 | —14| 100 1/ 100! —13 
4.35] 43 0 | — 1 68/— 4] 64 8! 100|—6/; 61] 
i 11. 00 43! 50 24 60 | 1 71 5 | 100) —11 76 | 
| January 15..... 7.35 32 84 28 67 43 21 6| 100} — 8 79 
4.35-|  26| 52 Br keer AO LAR 2; 100;—1] 68 
11 Ti 0} 100; — 4 64 
= 
bo 
wo 
ew 
a 
oa: 
_ 
= 
wo 
_ 
— 
ee 
“Salt Lake, at the western foot of the Wahsatch range, in the Great Basin, is con- 
stantly rather warm, and of ordinary humidity. Pike’s Peak is cold and constantly 
at its dew point. North Platte, on the plains east of the mountains, is much colder 
and distinetly drier. Denver and Cheyenne are much alike in changes of tempera- 
ture, as these stations are about equally distant from the eastern foot of the mountains ; 
but Denver shows much the greater decrease in relative humidity, perhaps because 
the range west of this station is higher than farther north. The second table shows 
in greater detail how violent the changes of temperature were at Denver and how 
completely they accorded with changes in the wind: 
Temperature and wind, Denver, January 14, 15, 1875. 

Date. Hour. eas Wind. 
- bad - 
| January 14 -..........] 2.43 p.m. — 4 NE 
9.00 p.m. | ny NE. | 
9.15 p.m. | 20) 1. SW | 
9.20 p.m. | 27 SW. 
9.30 p.m. | 36] SW. 
9.35 p.in. | 40 SW. 
“UN aa he 5.43 a.m. | 43 | SW. 
} 10.30 a.m. ba | SW. | 
| 12.30 p.m. 4/ NE. 
2.43 p.m. | atid BAe 
“An observer who was considered perfectly reliable says that between 11 a. m. and 
noon the thermometer fell from 58 to 22 (that is, 36°) 1n five minutes.” (Amer. Journ. 
)Science, 1875, x, 12; 18+0, xxii, 13, 14.) 
_ Any one who wishes to understand the climate of the Rocky Mountains will also 
do wel] to read an excelient paper on the Chineok-avinds by Prof. M. W. Harrington 
24738—Bull 2——16 

