66 AKSEL S, STEEN. TERRESTRIAL MAGNETISM. [NORW. POL. EXP. 
The deflection-observations were made in the usual manner, the deflector 
being placed successively in the well-known 4 positions. In each of these, 
the telescope was pointed towards the mirror of the deflected needle, where- 
upon the two verniers of the horizontal circle were read off, and also a 
reading was taken each time of the thermometer placed above the deflector. 
If we call the two circle-readings (mean of the two verniers) with the 
N-end of the declination-needle deflected in an easterly direction, w, and uw, 
and the readings with the N-end deflected in a westerly direction, #, and u,, 
we obtain 
g=y +4, 
where 
ais 2 ead 
AS eh ae” Darr? 
while 6 is the correction for angular inequality expressed in minutes. 
If we put wu, —u, = 4,, and wu, — u, = 42, and express 4, and 4, 
in degrees, then } 
é6=— A[si+ 4). 
As we know, the factor A has the following form: 
A = 052386 [} tan ym + } cot g], 
and according to this formula, I have drawn up a table for A for each 
single degree from gy = 3° to g = 70°, in order to simplify the caleu- 
lation of 0. 
The hour was unfortunately not noted for the separate settings of the 
needle during the actual deflections, but was noted at the setting of the free 
declination-needle before and after the deflections, and I have therefore tried 
by interpolation to fix the hour corresponding to the angle of deflection found. 
This interpolated hour is also assumed to be applicable to the reading of 
the needle’s position in the magnetic meridian, calculated by the deflection- 
readings, this calculated reading being entered, as mentioned on page 17, 
in the series of directly observed declination-readings. 
1 Lamont. Handbuch des Erdmagnetismus, p. 31, 
