376 . Astronomical and Nautical Collections. 



as 2.86 to 1 ; and supposing the Dip to have been 83° 04', as 

 was found by rather an indifferent observation, the theory would 

 require a diminution of 2.5 to 1. By the experiments of July 

 the force had diminished by Needle No. 2, as 3.28 to 1, and by 

 No. 3, as 3.198 to 1 ; the calculated diminution being 3.12 to 1 ." 



It does not appear that this connexion between the dip and 

 the magnetic force was ever before theoretically laid down, or 

 experimentally established ; it is, however, only an application 

 of the system of Aepinus and Coulomb to a hypothesis re- 

 specting the magnetism of the earth, which is perhaps partly 

 original, but which is the most simple and natural that could 

 be assumed. 



A strange assertion has lately been made, in a periodical pub- 

 licat;ion, "respecting the author of the paper in question, which 

 is, that he must have been ignorant of the existence of a plane, 

 in which a mass of iron, rendered magnetic by its temporary 

 situation with respect to the earth only, produces no effect in 

 the needle of a compass placed near it. 



. It is impossible that such an assertion could have been 

 made by one who had properly studied the grounds of the mo- 

 dern theory of magnetism, as laid down by Aepinus, by Dr. 

 Robison, by Haiiy, by Biot, or by any other good elementary 

 writer, and who had read the paper with any thing like 

 attention. 



The most superficial consideration of the nature of induced 

 magnetism will show, that a mass of soft or conducting iron 

 must become " a terrella," or earth in miniature, by the action 

 of the earth's magnetism ; and that as such, it must have its 

 magnetic equator, on which the direction of the magnetic 

 force is parallel to that of its magnetic axis, and consequently 

 to the magnetic axis of the earth ; and that when the needle is 

 situated in the plane of this aquator," it cannot be disturbed 

 by the magnetism of the terrella, which must act in the same 

 line as the force of the earth itself, though in a contrary 

 direction. 



That Mr. Lecount should have fancied this a new discovery 

 is not at all surprising; and it does him great 'credit to have 



