538 Lecture on a new property of Magnetism, 



I will throw the magnet out of its direction ; we shall get it round 

 this circuit. You will remember what this indicator did with the 

 bar magnet ; one end pointed at one pole and the other at the other, 

 and the thing travelled round and stopped parallel in the centre in a 

 curious way. See what it will do here. On making contact it is af- 

 fected ; you see that by the way the needle moves. But observe how 

 it is affected ; it is by an equatorial arrangement of magnetic force, 

 not by the polar one. If it were not so, the black end would point to 

 the surface, but you see how it dips or inclines to the surface. If the 

 earth had a magnetic pole, this end of the needle when suspended ver- 

 tically would point to that part. The needle, however, points down 

 into the mass of the earth soon after leaving the equator, and follows 

 that beautiful and curious relation which belongs to a single wire, when 

 the needle is carried round it. I have put up a rude diagram to 

 illustrate this. Suppose this were a part of the earth, and that were 

 a bar along its polar axis, a magnetic needle at the equator would 

 stand parallel to the horizon. A little further on, where our latitude 

 is, it would lose the horizontal line, and begin to dip until it stood 

 vertically. You will see the difference if I take an arrangement of 

 wire which is supposed to send electricity round the earth in place of 

 an internal magnet. The needle stands parallel to the horizon : it 

 soon dips when we get to our latitude : it dips in this shape : when 

 you get nearer the astronomical pole, the pole of the earth, it dips 

 very much ; but the dip is much more rapid if you assume the mag- 

 netism of the earth to depend upon these currents running equatori- 

 ally, than if you suppose it to depend on the polar axis. Instead of 

 the poles being at the extremities, they must in reality lie close 

 together at the centre of the earth. 



But whether the mangetism of the earth be due to currents run- 

 ning round the earth, or to a magnet fixed in the axis, the effect on 

 these bodies is precisely the same ; and all substances placed in a 

 line — and if placed in this room in relation to the rope before me — 

 would be affected in the same way as diamagnetic bodies ; that is to 

 say, precisely the reverse of the needle. The slice of apple, instead 

 of pointing axially, points equatorially. 



Now, I must briefly conclude by saying that if you consider, from 

 the experiments you have seen, that all the oceans, rivers, and lakes, 



