No. 7.] INCLINATION. 133 
The difference between this and the inclination I’ observed with the appa- 
ratus, will then be the index-error of B. The result of the calculations is 
given in the following table. 
84° 36°9'] 85° 31°3'} —54-4! 
84 373 | 85 293} —52°0 
85 23:1] 86 70} —43'9 
March 30 85 258 | 86 132] —474 
Mean 85° O08 | 85°50'2'| —49-4 
The mean value of the index-error found in this manner at an inclination 
of about 85°, differs so considerably from that found in Hamburg and 
Wilhelmshaven at an inclination of about 67°, that 7 can hardly be regarded 
as constant. Now if we had also had a determination of 4 at a place where 
the inclination is about 75°, we should, as already mentioned, have been 
able to determine all three constants, c, p, and @, in equation (1). As this 
is not the case, our only alternative is to put c= 0, if any regard at all is 
to be paid to the variableness of the index-error with inclination and total 
intensity. An assumption such as that the angle between the magnetic and 
the geometrical axes of the needle is infinitesimally small in proportion to 
the error in the inclination-determinations caused by the eccentricity of the 
centre of gravity, will also usually be perfectly justifiable, and upon this 
hypothesis equation (1) becomes 
4 =F cos (’ + a). (4) 
We then have the following corresponding data for the determination 
of the constants p and a: 
4 WwW Te 
Hamburg 1893 + eae 1897 17-0’ O-4774 68° 1:8’ 
Fram Expedition 1893-94 . . . . —494 0°5352 85°50°2’ 
If we substitute these values in formula (4), to which is given the form 
W4=«x cosI’—y sinl’, 
where # = pcos a, and y=psina, 
