502 POPULAR LECTURES AND ADDRESSES. 



made during this time on Bezout Island (the 

 nearest visible land), of the absolute values of 

 the three magnetic elements. The results were 

 normal. 



The instruments employed on board the ship 

 were the Standard compass, situated 68 feet above 

 the bottom of the sea, and a Fox dip circle about 

 6 feet higher. 



It was found that the centre of disturbance was 

 about 50 feet in diameter, and drifting slowly 

 over it from N.W. to S.E. three or four times, the 

 greatest disturbance experienced was from a force 

 repelling the north-seeking end of the needle, 

 amounting to 23 when on the N.W. side of the 

 centre, to 55 on the S.E. side. 



The ship was anchored for four hours nearly over 

 the centre of disturbance, the north-seeking end of 

 the compass needle remaining constantly repelled 

 as much as from 50 to 55. When exactly over 

 the centre the observed inclination or dip was 83 S., 

 the normal value for the general locality being to 

 the nearest degree 50 S. At this time the com- 

 pass showed but little disturbance. 



These large values of 55 in the declination and 

 33 in the inclination were confined to a very small 

 area, the values of the disturbance in both elements 

 decreasing rapidly as the centre was passed in any 

 direction. It was considered, from the observa- 

 tions made, that the whole area of disturbance 

 covered a space of one square mile. 



