Homogeneous Bodies ; 'with illustrative Experiments. 21 



few more of these plates or crystalline films may possibly be 

 the only parts excited ; and the rest of the bar assume the 

 character of a conductor only; in which case the current would 

 flow, at the point of heat, across the films from the internal 

 to the external parts of the cylinder; the direction which ex- 

 periment discovers it to proceed in : besides, it is possible that 

 the crystalline laminae may individually have different electric 

 powers. 



73. The other hypothesis supposes, that as the crystalline 

 strata are only in juxta-position, and not very firmly united, 

 it is possible that the heat applied at any point on the surface 

 of the cylinder would meet greater obstacles in its progress 

 whilst passing from film to film than any which it would fall 

 in with whilst flowing over the surface of those films, or over 

 the general surface of the metal: and as heat is well known to 

 affect electrical phaenomena generally, and as it is the exciting 

 agent in this particular class, it may be supposed that, by its 

 travelling at different rates in those directions, the electric 

 powers of the metal may also be put into motion, and assume 

 certain uniform directions as regards the directions in which 

 the heat flows with the greatest and least facility *. 



T^. Experime7its "joith solid Cones of Antimony. — When a 

 solid cone of antimony, uniformly dense on every side of its 

 axis, is made the subject of experiment, the surface near to its 

 base displays thermo-magnetic phaenomena of precisely the 

 same cliaracter as those which have been described in the ex- 

 periments with a cylinder (60, 61, 62). 



75. The cones which I have employed were 4*5 inches 

 high, and the diameter of the base 2*25 inches. 



76. When any of these cones were heated at any point of 

 the side near to the base, the current uniformly proceeded 

 from the point of heat over the surface towards the apex, 

 and returned on the opposite part of the surface to the base. 

 This was the direction of the lines of greatest energy, but 

 like the cylinder, the surface of the cone becomes generally 

 thermo-magnetic by this process, and the direction of its 

 forces are easily traced by the compass-needle. 



77. Fig. 15. will represent the surface of a cone of antimony 

 in a state of thermo-magnetic action: the cone is supposed 

 to be divided into halves from its apex to its base, and in 



• These hypotheses arc offered merely as conjectures, without any in- 

 tcntiun of insisting on either of them, until experiment affords more data 

 in their favour. If I mistake not, however, some of those whicii I have yet 

 to describe will bear directly on the subject. 



the 



