58 MAGNETISM. 



as nearly demonstrated by the experiments of Cou- 

 lomb, Lambert and Robinson. 



Dip of the Needle * 



A magnet placed in such a situation as to be en- 

 tirely at liberty, inclines one of its poles to the me- 

 ridian, and of course elevates the other ; this is called 

 the dipping of the magnet. In London it dips ; 

 at the north-west magnetic pole it would stand nearly 

 in a perpendicular direction. 



At Port Bowen the dip is 88 Lat. 73 14' N. 



Long. 88 54' W. 



Iron Railings and Carriage- Wheels. 



All iron bars standing erect or fixed perpendicu- 

 larly (such as the iron railings before houses) are 

 magnetic, the north pole being at the bottom, and 

 the south at the top. 



It is also a curious fact, that the uppermost part 

 of the iron ring round a carriage-wheel, attracts the 

 north end of the magnet, and is consequently a south 

 pole, while the lower part of the same iron, in con- 

 tact with the ground, attracts the south end of the 

 needle, and is therefore a north pole. Turn the 

 same wheel round half a circle, and these poles imme- 

 diately become reversed. 



Cannon Boring. 



The cutters in gun boring become magnetic in 

 consequence of being continually rubbed in the same 

 direction. 



* The Variation of the Compass was first discovered by Sebas- 

 tian Cabot, a Venetian, about A.D. 1500, and the variation of 

 that Variation by Mr. Gillebrand, an Englishman, A.D. 1625. 



The dip or inclination of the needle to a point beneath the 

 horizon, when allowed to play vertically, was first discovered by 

 Mr. R. Norman, about A.D. 1576. The diurnal variation of the 

 needle was discovered by George Graham in 1725. 



