3$ Force of Magnetic Attraction. [Book I. 



At 6 inches 3 grains. 



3 6." 



2 9. 



i 18. 



In contaft 87. 



This experiment would perhaps have been more, 

 intelligible, if it had been previoufly remarked that; 

 the attraction between the magnet and the iron is 

 always fuppofed to be mutual. If a magnet and a, 

 piece of iron are placed fo as to float on the furface 

 of water;, the magnet will approach the iron, as well 

 as the iron the magnet ; or if either of them are kept; 

 fteadv, the other will approach towards it *. 



Of natural magnets the fmaller poflefs a greater at- 

 tractive power, in proportion to their fize, than the 

 larger. There have been natural magnets of not 

 more than 20 or 30 grains in weight, which would 

 lift a piece of iron forty or fifty times heavier than 

 themfelves ; and mention is even made of one of 

 about 3 grams, which lifted a weight of iron contain- 

 ing 746 grains, or 2.50 times its own weight f. What 

 is yet mure extraordinary, it not unfrequently hap- 

 pens, that a loadftone cut off from a large one wilt 

 itfelf lift a greater weight than the ftone from which it 

 was cut off. This circumftance may reafonably be 

 attributed to the heterogeneous nature of the large 

 loadflone ; for if we fuppofe that one part of it, viz. 

 that which is cut off, contains a confiderable portion 

 of magnetic matter, and that the remainder is impure, 

 of confcquence, while they remain in an united ftate, 



* Adams on Magnetifra, p. 385. f Cav. on Mag. p. 36, 



the 



