264 Proceedings of the Royal Society, 



This being made to revolve at the rate of G40 turns per minute, 

 the needle was deflected out several degrees, and there remained 

 stationary during the motion of the ball, but returned immediately 

 to its original position on ceasing the rotation. On inverting the 

 motion of the shell, an equal and contrary deflection took place. 



As the law of the phenomena was not evident with this dispo- 

 sition of the apparatus, and the shell was found too heavy for 

 perfect safety, a Shaprnell shell of eight inch diameter was mounted 

 in a proper apparatus (described in the paper,) and a number of 

 experiments made, the law of which, however, still seemed ano- 

 malous, till the idea occurred of neutralising the earth's action on 

 the needle, when the anomalies disappeared, and the general law 

 of the effect was placed in evidence. The needle being made a 

 tangent to the ball, if the motion of the ball was made towards the 

 the needle (whatever was the direction of the axis of rotation,) the 

 north end of the latter was attracted, and if the contrary way, re- 

 pelled. In the two extremities of the axis there was found no 

 effect ; while in two opposite points at right angles to the axis, 

 the effect was a maximum, and the direction of the needle was to 

 the centre of the ball. 



The author then proceeded to shew how the results, which before 

 appeared anomalous, agree with this general view, and closed his 

 communication with some theoretical views of their general bear- 

 ing on the subjects of the earth's magnetism, which he thought 

 there were strong reasons for believing to be of the induced 

 kind, and although it appeared to him doubtful whether the ano- 

 malies observed in the variation of the needle on the earth's sur- 

 face, can ultimately be referred to this cause, yet he observed that 

 one condition essential to the production of these phenomena, 

 holds good in the case of the earth, viz., the non- coincidence of 

 its polarized axis with that of its diurnal rotation. 



A paper, On the Alteration in the Magnetism of an Iron Plate, 

 occasioned by a Rotation on its Axisy by J. H. Christie, Esq., was 

 communicated by the President. 



The effects observed and described in this paper, although mi- 



