602 



METEOROLOGICAL OBSERVATIONS. 



BAROMETRIC AND METEOROLOGICAL OBSERVATIONS, MADE DURING THE SURVEY OF A LINE FROM 

 COLUMBIA BARRACKS TO FORT COLVILLE, AND THE RETURN; BY LIEUTENANT S. MOWRY, U. S. 

 ARMY. 



Comparison of barometers. The mercurial barometers are designated as &quot;standard,&quot; &quot;No. 1&quot; 

 and &quot;No, 2;&quot; the first of which was left at Columbia Barracks and regularly observed for nearly 

 five months. The mean of its readings for this period gives quite accurately the known altitude 

 of Columbia Barracks above the sea, and it may therefore be taken as without zero error, though 

 no comparison of it with an absolute standard exists. Barometer &quot; No. 1&quot; reads so nearly with 

 this &quot; standard&quot; from July 1st to July 18th, the time of departure, that no zero correction need be 

 introduced. This barometer is carried nearly to Fort Okinakane. and may be used for all the 

 determinations of altitude. Barometer &quot;No. 2&quot; differs considerably at Columbia Barracks from 

 either, and continues to differ as far as it is carried, which is to camp 28, &quot;on the north branch 

 of the Columbia,&quot; by between two and three tenths of an inch. It is doubtless nearly so much in 

 error ; and as its readings do no appear necessary to any determination, they are not given in the 

 tables. 



The aneroid barometers, Nos. 9445 and 7992, are compared at Columbia Barracks and used 

 after the mercurial instruments are broken. Their readings are quite irregular, and Lieut. Mowry 

 places little confidence in them. When they have an approximate accuracy or possible value, 

 they are transcribed with the journal, but no altitudes are computed from them. At the return of 

 the party they differed from the &quot; standard&quot; by very large measures. 



Barometers &quot; No. 1 &quot; and &quot;No. 2&quot; were syphons. It does not appear whether the &quot; standard&quot; 

 was an open cistern, (brass,) or Alexander s mountain barometer, the vernier of which is adjusted 

 to a glass column only. The correction for temperature is somewhat less in this case than for an 

 open cistern with brass scales. The correction for brass scales is, however, applied to all the 

 readings of the barometer retained at Columbia Barracks as the &quot;standard.&quot; 



Barometric Readings at Columbia, Barraclcs. 



