No. 7.] HORIZONTAL INTENSITY. 65 
The two distances at which the deflectors can be placed, are, as pre- 
viously stated, 
e = 29°840 cm. 
E = 39°638 
so that the proportion between e and £ is as 1: 1°33. By experiments in 
” 
Hamburg during the construction of the instrument, the distances were 
chosen with a view to giving the deflection angles in the polar regions, where 
the horizontal intensity is very small, a suitable, not too great, value. 
According to the formula ; 
oi oe Hsin Do 
H 
where H, indicates the horizontal intensity in Hamburg, and y, the angle 
of deflection found during the experiments there with the apparatus, Dr. 
Neumayer calculated the angle of deflection for Kristiania, Tromsé, and the 
polar regions, assuming for these localities a horizontal intensity of respec- 
tively 0°1616, 0°1228, and 0:0500 (C. G. S.), with the following result: 
Place Magn. VI 
Hamburg. ... re f 16°75 70 
Karis tania ace 9 fi 187 78 
‘RromsGiee-7 vue sae 5" ; 25°0 10°3 
Polar Regions. . 261 
After this, it would always be possible in the regions which the Fram 
might traverse, to obtain efficient deflection-observations with magnet V at 
both distances, while magnet VZ would in most cases probably only be capable 
of being employed at the greater distance #. It is also probable that it 
would be more advantageous on the whole for magnet V to use the greater 
distance. These hints were followed. ‘During the expedition, there were, on 
the whole, 163 angles of deflection determined, 132 of them being with 
magnet V, and 31 with magnet VZ. In the 152 cases in which magnet V 
has been used, y was determined 79 times with the deflector at the distance 
E, and 53 times with the deflector at the distance e, both distances being of 
course employed simultaneously when opportunity offered. Out of the 31 
determinations of the angle of deflection with magnet VJ, the short distance e 
has been used in only 4 cases, 
