132 AKSEL S. STEEN. TERRESTRIAL MAGNETISM.  [NoRW. POL. EXP. 
about the same value on both the days mentioned. The same assumption 
is also possible in the case of the last two observation-days, February 10th 
and March 30th, 1894. There are thus two groups of observation-data, from 
which ¢ may be calculated, supposing that R, has remained constant during 
the period of a few weeks which each group embraces. We then obtain 
pee sin W. — sin Wr" 
> tsin pw.’ — t sin wy’ 
when wy. and w,’, £ and ¢ indicate the angle of deflection and the tempe- 
rature observed respectively on the first and the second of the two days of 
the groups in question. The calculation gave the two following values 
for ¢: 
C 
1893. Oct. 16 and Dec. 2 . . . . —0-0001979 
1894. Feb. 10 and March 30. . . —0:002435 
Mean — 0:00132 
Although this result cannot naturally lay claim to any great degree of 
accuracy, I have thought it possible, in the absence of anything better, to 
make use of it, and have therefore, with ¢ = — 0:00132, calculated R, by 
the observations in Hamburg in 1893, and in Wilhelmshaven in 1897, and 
have found, 
R, 
for June 9, 1893 . . . 041198 
» April 20, 1897. . . 041054. 
Starting with the supposition that R, has decreased proportionally with 
time, I have been able, by graphic interpolation, to deduce the following 
values for the above-mentioned 4 days, viz. 
R, 
1693; Och 16es, coals 
Deew2-< fey. 0411S 
in 1894, Feb. 10. . . . 04117 
March 30 . . . O-4117. 
By substituting these values in formula (3), we obtain the total intensity 
W, which, together with the corresponding values of the horizontal intensity 
specified on page 131, give the actual inclination J, according to formula (2). 
