EXPEDITION TO POINT BARKOW, ALASKA. 457 



PART II. ABSOLUTE MEASURES. 



MONTHLY VALUES OF THE MAGNETIC DECLINATION, DU', AND INTENSITY AT UGLAAJIIE, DE> 



CEMBER, 1881, TO AI'GUST, 1883. 



The horizontal direction of the magnetic force at Uglaamic was determined by means of Fa-nth 

 & Co.'s magnetometer, Coast and Geodetic Survey, No. 11, mounted on the northern pier of the 

 magnetic observatory built soon after the arrival of the party. In July, 1882, it was shifted to a 

 new position, where it remained to the close of the work. This instrument served both for the 

 absolute as well as for the differential or variation measures; the latter observations, however, 

 were discontinued on the arrival in the second year of the, Brooke variation instruments. The 

 instrument was not well adapted for differential work, as lias been stated. 



From returns brought home in the Leo, it was evident that the declinations Were defective, 

 for some reason not then apparent; also, that the magnet, which was a new one, had parted with 

 much of its magnetism. It became desirable, therefore, practically to test, the condition of the 

 instrument for accurate work as soon as this could be done, ft was returned to the office at. Wash- 

 ington January 12, 188-1, and after undergoing some trifling repairs, due to defective packing, 

 Sergeant Maxfield was directed to determine the declination with it at the magnetic observatory 

 in this city,* also to furnish some additional measures of the. instrumental constants, those; obtained 

 by Sergeant Smith in June, 1881, not being deemed sufficient. These measures proved that the 

 instrument was still in a satisfactory condition. 



When the full returns came to hand it became evident that the discrepancies noticed in the 

 monthly values of the declination were due to a want of attention to the suspension fiber. The 

 plane of detorsion was apparently placed in the magnetic meridian in December, 1881, but no. 

 further test or adjustment was made till March, ISS.'j. During this period the force of torsion had 

 gradually increased (from unknown causes) and affected the declination to the amount of nearly 

 .~>.p in September, 1882. After this date this deflection remained perfectly steady, until removed 

 in March, 1SS.',. 



For the first six months the monthly results refer to the mean declination of the day (from 24 

 hourly values), but after the arrival of the Brooke differential instruments the declinations were 

 referred to the mean of the respective months through hourly corresponding readings of the Fauth 

 & Co. magnetometer No. 11, and the Brooke declinometer. These corresponding readings generally 

 extend over hours on each day of observation. 



The record and computation of the absolute measures are contained in accompanying Appen- 

 dix No. 2. Placing little reliance on the determination in December, 1881, on account of a weak 

 astronomical azimuth, and omitting for the present all results of 1882 and those for 1883, up to the 

 middle of March, we have the following reliable values, which rest on a new astronomical azimuth, 

 determined July 25, 1882, and which are roughly checked by a second measure, taken on the 

 Brooke declination pier August 31, 1882, the same markt being used and all distances being known. 

 The observations of July 31 are rejected, there being apparently an error of about 44: 



* The observations made February 5 and 7, Iwl. gave for i In- dec! i nut ion :'. .~>7'.'J W. The same computed from 

 iinniiiiJ obser\ utions inside ,-it Washington, 1 >. '.. sincv, 1.-77. is .1 Of) .-1 W. : ilitlerenec, y'.fi The measure* for intensity 

 w< re equally satisfactory. 



t Distance magnetometer No. 11 to murk 1)00 feet, ami to llrookc declinoiiioter, :i'.l.r> feet. First position of instru- 

 ment November vM, |.-<*1, azimuth of mark on house, 06 l:V W. of N. from observation on Jupiter: second position of 

 instrument, July 2.1, IHHi, mark 4<i 3G' K. of N. from observation of the sun. 

 JI. KX. 44 58 



