Chap. 6J] Hew the Magnetic Power is diminljhed. 5 1 



placed a fmall magnet, exactly at fuch a diftance, that 

 the power of the magnet at the fouth pole was jtift 

 fufficient to keep the north end of the needle to the 

 N. E. point, or 45 degrees. He contrived to heat the 

 magnet, by putting upon it a brafs veffel, into which 

 he poured about two ounces of boiling water, and as 

 the magnet gradually heated, he obferved, during 

 feven or eight minutes, that the needle moved about 

 three quarters of a degree weftward, and became fta- 

 tionary at 44 f ; in nine minutes more it came back 

 a quarter of a degree ; but it was fome hours before it 

 gained its former fituation, and flood at 45 *. 



jd. In general the fame means which facilitate the 

 communication of magnetifm to ferrugineous bodies 

 not magnetic, tend to deprive thofe which really are 

 fo of the magnetifm they have acquired. Every kind 

 of violent percuffion weakens the power of a magnet; 

 and a very ftrong magnet has been entirely deprived 

 of its virtue by receiving feveral fmart ftrokes with a 

 hammer j-. This effect appears to depend chiefly on 

 the derangement of the particles in the magnetic bo- 

 dies. TJius, if a dry glafs tube is filled with iron fil- 

 ings, magnetifm may be communicated to the tube by 

 touching it with a loadftone, exactly as if it was an 

 iron bar 5 but the lead agitation which difturbs the 

 fituation of the filings will prefently expel the magne- 

 tic virtue J. 



4th. In the fame manner the electric ihock, which 

 imparts the ftrongeft virtue to iron not previoufly 

 magnetic, v. ill diminifh, and even deitroy, the power 

 of a real magnet. Electricity will alfo fometimes' in- 

 vert the poles of a magnet . 



* Adams on Mag. 417. f lb. 443. \ Ib. 444. 

 5 Cav. part i. c. 7 ; and Adams on Mag. 446. 



E 2 The 



