90 &. Loomis—Observations of the U. S. Signal Service. 
shows the differences between the numbers in the two preceding 
columns. 
Mt. W. |Bur. & Port Diff. | Mt. W, |Bur. & Port Diff. 
January 29°724| 30°054 |—0°330)|July 30°225| 29°929 |+0°296 
February 693) 29°984 |— -291||August 282} 30°008 |+ -274 
March “115 ‘927 |— -212||September 16 003 162 
April 873 "930 |— °057 r 015) 29°996 |+ ‘019 
May 30°039 935 |+ °104!|November | 29°836 ‘979 |— 143 
June 153 926 |+ °227\|December 695; 30°004 |— °309 
We thus find that by employing a constant reduction to sea- 
level for all months of the year, the pressure for Mt. Washing- 
ton in January is made 0°33 inch too small; and the pressure 
in July is made 0-296 inch too great. 
- A similar error must exist in the reduction of the observa- 
tions at the Rocky Mountain stations, but it is more difficult 
to determine its exact amount, because the nearest stations of 
comparison which are situated less than 1,000 feet above the 
level of the sea, are distant over 500 miles. Under these cir- 
cumstances I have endeavored to reduce the observations at 
each of the mountain stations to the level of the sea, for each 
month of the year, independently. The chief difficulty in 
making this reduction arises from the uncertainty as to what 
should be regarded as the temperature of the point situated at 
the level of the sea and directly under a given mountain station. 
The following is the method which I attempted to employ. 
determined for each month the mean temperature of a point on 
the Pacific coast, and also the temperature of a point in the 
Mississippi Valley, each having the same latitude as the given 
station. Between the two temperatures thus determined, I 
interpolated a value corresponding to the differences of longl- 
tude between the given station and the two points above named. 
The following table shows the required data for the month 
of January and the results of the computation for each of the 
stations (except Mt. Washington and Pike’s Peak) for which 
the reduction to sea-level by the Signal Service is made by the 
addition of a constant quantity. 
ee eee 
Temperature. | Reduc. tos, levy.} Mean barom. 
iy a ee 
: Eley., : 
Stations. Lat. | Long. fe0t. | station | Rane. Big.s. Comp. Big. 8 ‘ or 
ce halal 
Santa Fé | 35 41|10610| 6862 | 29°76! 46°32| 6-54 | 6-81 | 29°733| 30°00 
39451105 4| 5162 | 26-14| 36-23| 5-22 | 5-37 | 29-944] 30° 
Cheyenne | 4112|10442| 6057 | 23-26 31-80] 5-94 | 6-26 | 29°850| 30°17 
0/112 0| 4362 | 29° : ; 4°6 Sood 
Corinne 41 30/112 18| 4249 | 28-30/ 37-29| 4:25 | 4-63 | 30-116] 30°39 
Virginia ©. | 45 20/112 3| 5480 | 16°82| 27-21] 548 | 5 93 
Benton | 4752'11040! 2674! 8-28| 19°20! 2-90 | 3-04 | 30-008] 30°15 
