72 AKSEL S. STEEN. TERRESTRIAL MAGNETISM. [NORW. POL. EXP. 
to take observations in the polar regions. He therefore recommends the 
making, if possible, of a direct determination of this coefficient upon the field 
of observation itself. There was no opportunity, however, of making such 
delicate investigations in the difficult natural conditions with which the 
expedition had to contend; and it is thus only a question of deducing indirectly 
from the series of observations a reasonable value for a, and this only for 
magnet V, which was the one most frequently employed. 
With this object in view, I first took all the cases in which both the 
vibrations and the deflections had been observed with magnet V on the 
same day, and the double needle had been employed as deflected magnet. 
Assuming for the time being that the horizontal intensity on the above- 
mentioned days had been the same during both the deflections and the 
vibrations, I was able, for the determination of a, to draw up by formula (6), 
39 equations in the form 
inal PY ge athe 
ah Vsing 
u— [tt ae— aoe], 
which fall into two groups, 15 with the deflector at the distance e, and 24 
with the deflector at the distance H. As the constant value of u, I employed 
the mean of the values found in Hamburg and Wilhelmshaven, in 1897. 
The mean value of @ from the first group of equations was 
a = 0000431, 
from the second 
a = 0000567, 
and from the entire 39 
a = 0:000514. 
With this value for «, and the mean values for « and C, found by the 
determinations in Hamburg and Wilhelmshaven in 1897, a temporary value 
for H was calculated by formule (4) and (5) (page 64) separately by 
vibrations and deflections i the above-mentioned 39 cases. It then appeared 
that in only 7 of these cases did the values for the horizontal intensity 
deduced from the vibration and deflection observations made on the same 
day, agree so far that there could be any question of using the observations 
for determinations of constants. These 7 days were: 
in 1894, December 7th, 
» 1895, May 24th, 
