114 Mr, Christie on the Magnetism of Iron [Aug. 



the same time suppose a source from which magnetic influence 

 is deri\'^d. Is it not then possible that the sun may be the 

 centre of such influence, as well as the source of Hght and 

 heat, and that by their rotation the earth and other planets may 

 receive polarity from it ? If so, further experiments and ob- 

 servations on the magnetic effects produced by the rotation of 

 bodies may indicate the cause of the situations of the earth's 

 ma^etic poles, and of their progressive movements or oscil- 

 ^ lations. 



Comparison of the inagnetical effects produced by slow and 

 by rapid rotation, 



** With the view of ascertaining how far the effects produced 

 ^on a magnetic needle by a plate of iron during its rapid rotation^ 

 Ttorresponded with those that I have described as nearly inde- 

 pendent of the velocity of rotation, and as continuing after the 

 rotation had ceased, I placed the same plate of iron, which I 

 hidid used in my former experiments, in the plane of the magnetic 

 meridian, on an axis perpendicular to its plane, and about 

 which it could be made to revolve with any velocity, not ex- 

 ceeding 10 revolutions in a second. I then placed a small 

 compass, with a light needle delicately suspended, on a plat- 

 form wholly detached from the iron plate, in certain positions 

 opposite lo the edge of the plate, both to the east and to the 

 west of it, as near to the surface as the compass box would 

 admit. The compass being adjusted, the plate was made to 

 revolve once, slowly, so that its upper edge moved from north 

 to south, and the point coinciding with the plane perpendi^- 

 cular to the plane of the plate, and passing through its centre 

 and that of the needle, the direction of the north end of the 

 needle was observed ; and also when 180 coincided with the 

 plane, the same observation was made. The plate was now 

 made to revolve rapidly in the same direction, about 8 

 times in a second; and when the needle became stationary 

 during the rotation, the direction of its north end was observed. 

 The point on the plate was again made to coincide as quickly 

 after the rapid rotation as possible, and the direction of the 

 needle observed, in order to see if that rotation had produced 

 any permanent change in the iron ; the same was done when 

 the point 180 again coincided. Observations precisely similar 

 to these were made when the upper edge of the plate revolved 

 from south to north. 



" Although the centre of the plate was stationary, and the 

 needle was placed in certain positions with respect to it, I con- 

 sider, as before, the situation of the centre of the plate with 

 reference to the plane passing through the centre of the needle 

 perpendicular to the dip ; and its angular distance fiom this 



