74 AKSEL S. STEEN. TERRESTRIAL MAGNETISM. [NORW. POL. EXP. 
show that « cannot be constant, but, as we have already supposed, must 
depend upon the temperature. If we call this z, we may put 
<= 
a=a, +agt, 
and equation (6) becomes 
po Weing ! + gt — ger +0, Fh 4, a () 
if ¢ and ¢ have anything like the same value. This equation affords an 
opportunity for the determination of «, and a, by the method of least 
squares, as we obtain a series of equations in the form 
B 
a, +b Aa, = A’ 
where 
es la a ee E + et— 9 e'|. 
2 Vsin 
After a careful study of the forthcoming observation-data, which deter- 
mined me in excluding two of the above-mentioned normal days, namely 
June 18th, 1896, and March 2nd, 1897 (Hamburg) — it being likely that the 
observations on these days were more affected by disturbing forces than on 
the other normal days — I finally retained 12 corresponding values of A and 
B, employing the mean value of the constant « used in the provisional 
calculation of «By the aid of these 12 values of A and B, I have been 
able to draw up the following normal equations: 
12a, — 999a, = 0:0043426 
— 99°9 a, + 3462°95 «a, = — 0:045605, 
which give 
a,= 0°00033198 
a, = — 000000359 , 
and thus @ = 0:00035198 — 0:00000359 c. 
By this formula, which I consider to be the final one, I have calculated 
a table for «, for magnet V, with the temperature as argument, for every 
degree from — 40° to + 20° C. 
I have been compelled to abandon a similar examination of the tempe- 
rature-coefficient for magnet VJ, that magnet having, as previously stated, 
been comparatively so seldom used, that the observations that we have do 
