50 



COMMANDER JAMES CLARK ROSS ON THE POSITION 



its position in nearly the same amount as the arc described by the point of suspension, 

 showing that the smallest amount of torsion was sufficient to overcome the directive 

 energy of the needle. 



The needle was now removed to the dipping apparatus, and the following observa- 

 tions on the intensity of the vertical force of the needle were obtained, upon the sup- 

 position, that in whatever direction a given number of vibrations in the same arc were 

 made in the shortest time, that might be assumed as the magnetic meridian. The 

 direction of the needle is given in true bearings. 



50Vib»«in 1 502 1 50 1 50-5 1 51 1 51*2 1 50 



From these observations it was equally impossible to assign a direction to the mag- 

 netic meridian, the slight differences being within the limits of the errors of observa- 

 tion, and the amount of the inclination or dip of the needle in each of these directions 

 being precisely the same. A diminution of force, however, may seem to obtain in 

 the directions of S. 10°E. and S. 40°E. ; and a direction at right angles to that, 

 S. 75° W., I assumed as the magnetic meridian in the first two sets of dip. The 

 mean of these was 89° 58' 15". The next two sets were taken at an angle of 45° to 

 the right of the former, and their mean result was 89° 59' 46" ; and the two last sets, 

 exactly at right angles to the first set, gave the dip 89° 59'. In these last observations 

 the axis of the intensity needle was put in the stead of its own axis, which accounts 

 for the difference in the readings of the needle in its several positions, as will be seen 

 by the table of dips. The reason for my doing this was to provide against the possi- 

 bility of the observations being influenced by an injury which the axis of the needle 

 was supposed to have sustained, by the great difference that sometimes occurred in its 

 indications. The result of these observations, however, shows that the injury, if it 

 had met with any, did not materially affect the results ; so perfectly do the principles 

 of its construction counteract any slight bend in the axis, or any inequality in the 

 balance of the needle. 



To complete the observations on the intensity of the magnetic force, and the various 

 experiments which were made, and which it is unnecessary here to notice, occupied 

 the whole of the time that I could devote to that purpose. And although there is a 

 difference, amounting to several minutes, in the different observations made in the 

 same direction of the needle, yet the resultant mean dip in each of the three directions 



