320 Rev. Mr Scoresby on the Unifbrm Permeability 



lions, and combinations, all are perfectly permeable, and, as it 

 were, quite transparent to the magnetic influence. And if so, 

 we have a strong probability, by simple inference, that every sub- 

 stance in nature is equally permeable. 



In regard to substances not ferruginous^ a great variety has 

 been subjected to trial, and these of various solidity, condition, 

 and thickness ; but in no case has any perceptible hinderance 

 been offered, either by one substance, or by a variety of diffe- 

 rent substances in combination, to the transmission of the mao-- 

 netic influence. The principal substances to which iny ex- 

 periments have extended, are stone, wood, and metals of vari- 

 ous species ; brick, earth, water, paper, leather, hair, feathers, 

 wool, plastering, glass, rosin, and also the skins and bodies of 

 different animals. The thickness of the different substances has 

 of course been very various, from a few inches to many feet, or in- 

 deed to several yards. The magnetic influence employed in 

 these experiments was chiefly that of three pairs of bar-magnets 

 constructed under my own direction, a pair of one foot (C), a 

 pair of two feet (B), and a pair of three feet in length (A) ; and 

 the instruments for determining the degree of influence consisted 

 of a pocket compass by Dolland, and one of Captain Kater's 

 azimuth or surveying compasses. 



The nature of the experiments simply consisted in the ob- 

 servation of the angle of deviation in the needle of the compass, 

 under the action of one or two magnets, with different soHd sub- 

 stances successively interposed between the magnets and the 

 compass ; and then comparing the deviation so obfained with 

 the deviation produced at an equal distance, and in the same 

 direction, when nothing solid was in the line of the attrac- 

 tion. And in all cases the corresponding deviations at equal 

 distances, were precisely the same, whether there was a mass of 

 stone, wood, earth, or other substance, though of several feet in 

 thickness interposed, or whether there was nothing. Thus the 

 smaller magnet being placed at 13 J inches from the com- 

 pass, in the line of the west point (that is, at right angles to 

 the magnetic meridian) produced a deviation on the needle of 

 35° ; but when a large mass of ivory, a lot of books, a thick 

 block of fossil wood, an electrophorus contained in a tinned 

 iron case, first in its neutral condition, and then excited, with a 

 variety of other solid substances, were successively interposed. 



