EXPEDITION TO POINT BARROW, ALASKA. 



461 



ABSOLUTE MEASURES : HORIZONTAL COMPONENT, VERTICAL COMPONENT AM) TOTAL MACNETIO 



FORCE. 



The observations for horizontal force were made with magnetometer Coast and Geodetic .Survey 

 No. 11, mounted on its pier in the small magnetic observatory ; on its return to Washington in 

 January, 1881, the glass tube was found broken; it was replaced by a spare tube, and after repair- 

 ing some trilling damages, additional observations were made here by Sergeant Maxlicld for a 

 better determination of the instrumental constants.* He also made the observations of deflections 

 by gravity and by magnetism with the Lloyd needle of dip-circle No. 23, which were required to 

 furnish the constant for converting relative total intensity into absolute measure. 



Constants of magnetometer So. 1 1 : Mass of ring 300.767 grains, outer diameter 3.779 cm., inner 

 diameter 2.953 em., thickness 0.52!) cm., measured April 29, 1881, at 77 Fah., again from, meiisun's 

 on April 30 at 73 Fah. outer diameter 1.4895 inches, inner diameter 1.100 inches, thickness 0.208 

 inches ; the ring is of bronze. Moment of mass MI at any temperature t (Fah.) in units of feet 

 and grains=0.93070 [1 +.00002 (t 75)]. From observatious of oscillations of long or intensity 

 magnet L u with and without ring, by Sergeants Smith, in June, 1881, and Max field, in January, 

 1884, we have at the temperature of 62 Fah. : 



hence M for any temperature t (Fah.), Jf=O.S7G94 [1+.0000136 (t 02)j; length of collimator 

 magnet L n 2.48 inches, diameter 0.33 inch about; length of shorter magnet Sn 2.04 inches, diani- 

 ter 0.34 inch about. Scale of declination magnet L u , 80 divisions; angular value of scale 3'.69 

 The temperature coefficient determined from the monthly observations of the intensity at Uglaamie 

 was found to equal </=. 00085, a value rather large and probably related to the rapid loss of mag- 

 netism of LJI when first magnetized; the magnetic momentum of this magnet changed from about 

 0.0693 (English units) in December, 1881, to 0.0671 in January, 1884. 



From the monthly observations at Uglaamie the following results were deduced: 



Tabli <if reuniting values for magnetic horizontal force (H) at Uglaamie, as determined by magnetometer 

 No. \\ from oscillations and deflections, and expressed in Knglisli unitx. 



Mean horizontal component of magnetic intensity from 21 months of observation 1.939, (English 

 units), for epoch October (middle), 18S2. Annual apparent increase, +0.015 



"The following ivsiilts \vcrr deduced from Sergeant Maxfield's observations at Washington : January --i- 1 . 1^64, 

 H-4.\n'> (English units) ; dip January 30, 31, February 1, 2, 1884, 0=70' :!?'.:!, licin-c /'~l:U! J .~> These results com- 

 pare favorably with this values deduced (and refenvd to sann- time) from 1.S years of annual determination* in the 

 name place, vis, // -4.378, 6=7<T :).'4, 7-=13.'21H 



t OKcillations alone on January 18, 19 and April 17. 



