14 AKSEL S. STEEN. TERRESTRIAL MAGNETISM. [NoRW. POL. EXP. 
It will be seen from this table, which contains 122 different determinations, 
that the values found vary from + 44-4 to + 11:6’, without its being possible 
to find any decided change with time, if the values are plotted graphically. 
We may therefore certainly assume that the error of collimation has in re- 
ality remained constant all the time, and its most probable value will thus 
be the mean of the 122 determinations, i.e. + 30°1’, which accords fairly 
well with the value found in Hamburg in 1893. If we omit from the table 
all the values whose difference from the mean is greater than + 10’, and 
which are indicated by brackets[ ], this has no effect upon the result, as the 
mean remains the same, + 30°1’; and if the values obtained by the deter- 
minations in Hamburg in 1893, and in Wilhelmshaven in 1897, be added, 
+ 30° and + 37:7’ respectively, the mean still remains unchanged. I have 
therefore deemed it advisable to take this mean, + 30°’, as the constant value 
of the error of collimation. The sometimes great deviation shown by a few 
of the figures in the table, may be easily explained by the mobility of the 
needle owing to the low force of direction, and the magnetic disturbance which 
constantly prevails in the polar regions. Captain Scort-Hansen has informed 
me that the needle was always oscillating more or less widely and quickly; 
and if we moreover consider that the needle was not suspended by a thread, 
but rested upon a pivot, the results here given may well be deemed as satis- 
factory as it was possible, under the circumstances, to have them. 
THE SMALL NEEDLE. 
In the passage from point 7 in Dr. Neumayer’s manuscript quoted in 
the introduction, a case is mentioned containing two reserve needles for de- 
clination observations. Only one such needle accompanied the apparatus, and 
it was moreover intended more especially to act as the deflected magnet in 
deflection observations for the determination of the horizontal intensity. This 
needle is a little shorter than the declination needle proper, having a length 
of 70 mm.; and it weighs 21-2 grammes. As it cannot be reversed, its error 
of collimation was found during the determination of constants in Hamburg 
in 1893, by several series of comparative observations with this and the true 
declination needle (double needle), the result being that a declination deter- 
mination with the small needle gave a declination that was 8.6’ more easterly 
than the true one. A correction of — 8°6’ must therefore be added to all 
