VOL. XXXI.] PHILOSOPHICAL TRANSACTIONS. 529 



the upright needle to the centre of the compass might be perpendicular to the 

 compass needle. Then observing the same caution, which was convenient to 

 make the centre of the compass serve sufficiently well to be esteemed its centre 

 of power, I placed the upright needle at several greater distances, every time 

 marking the place in the manner already described, and observing the variation 

 of the compass. By this means I got a curve pretty regularly and fairly drawn 

 by points on the paper. And by examining this curve, compared with the va- 

 riations of the compass corresponding to its respective points, I found that the 

 magnetical power decreased faster at the greater distances than at the nearer. 

 It is of little use to be very particular in the account of the several observations. 

 I shall only take notice, that at about 2^ inches distance, the force did not 

 alter so fast as the squares, and at JO inches distance, where the variation was 

 one degree only, it altered faster than the cubes, the index of the power being 

 about 34-. The needle of the compass was so short, that to suppose its centre 

 of force to be either in the middle or at the extremity of it, would not alter 

 the index of the powers of the distances -^ of a unit. 



I made another experiment to the same purpose, with a compass needle 

 made of a slight piece of straw, with a small piece of steel- wire fastened to 

 one end of it, which was always kept in the same position, being balanced 

 between two perpendicular needles, one of which was moveable, and the other 

 fixed. The event was much the same as in the former experiment. 



Endeavouring to find the true poles or centres of the magnetical power in 

 touched needles, I made a needle of 2 inches long, of the fine steel-wire, 

 which I touched with the south point of a small capped loadstone, applying the 

 point of the cap only to the extremity of the needle, without drawing it along. 

 The needle so touched, being laid gently on the surface of a stagnant water, 

 floated. I then applied to it successively the two ends of a touched needle, 

 as near as I could, without letting the needles touch. The result was, that the 

 floating needle rested under the respective poles of the other needle marked 

 with the small letters s, n, s. So that by one n s n $ 



touch with the loadstone, which gave the ' ' ' i 



needle a north-pole at n, where it was touch- i 1 1 | 



ed, it acquired three other poles, s, n, s, ^^5[ f ^ .^ ■'^ 



which we may not therefore improperly call n s N s n S 



its consequential poles. Having: discovered \Z ' ' ' ■ ' 



1 .• 1 1 1 1 . N s n S n s N 

 these consequential poles, 1 made some other i 1 1 1 1 1 1 



experiments to discover more of the nature of them, as they are described in 



the scheme annexed. The needles were each 2 inches long, made of the same 



fine steel- wire, and the letters N, or n, and S, or s, denote the character of 



VOL. VI. 3 Y 



