No. 7.] HORIZONTAL INTENSITY. 63 
where C is a constant quantity of the following form: 
C= 0 PRE [1 — ae a+ 4sin pH]. (2) 
e 
As already mentioned, there are two magnets belonging to the apparatus, 
designated V and VJ, respectively 99°0 mm. and 98:0 mm. in length. 
The temperature coefficient « was determined for both of them in Hamburg 
on June 8th, 1893, by a long series of observations, after they had been 
placed, on June 3rd and 4th, in steam of 100° C., and kept there for 12 
consecutive hours, in order to ensure them against loss of permanent mag- 
netism afterwards. 
The following values were found: 
a 
For magnet V. . . . 0:000307 
es — VI... . 0:000638 (?). 
The moment of inertia of the magnets, K, was also determined on 
June 9th, 1893, from several series of vibration observations, alternately 
with and without the addition to the magnet of a ring of known weight 
and dimensions, with the following result, which, however, does not lay 
claim to any great accuracy: 
K 
For magnei V ... . 99°47 
4 th ME crt Saree DIOP 
The induction coefficient cannot be directly determined with this in- 
strument. 
The total constant, C, in which both the moment of inertia and the 
induction coefficient are included, may, however, be inferred by means of 
equation (1), if combined vibration and deflection observations are taken with 
the instrument, in a place where the horizontal intensity is known, as the 
following equation is then obtained: 
log C = log H+ log T+ 4 log sin p — log[1+ p’t — 28 + a(¢—?)] (3) 
The observations for the calculation of the constant C were made in 
Hamburg before the departure of the expedition, and in Wilhelmshaven after 
its return. 
As it was to be expected that there might often be occasions during the 
Fram Expedition, when there was no opportunity of observing simultaneous 
