On the Thermo-Magnetism of Homogeneous Bodies. 117 



the directions of the electric currents as indicated by the de- 

 flections of the magnetic needle, when the point of heat was 

 near to the angles a, b, c, respectively. 



92. When the spirit-lamp was held for a few moments at 

 the angle a, still keeping the point of the flame on the face 

 of the fracture, the electric streams were diff"used over every 

 part of that surface y?o??2 the point of heat towards the op- 

 posite edge; as shown by the directions of the arrows, fig. 16. 

 Comparatively strong currents were detected in the edges a 6, 

 and ac; but in consequence of the general flow of these cur- 

 rents being nearly at right angles to the edge b c, no magnetic 

 force could be detected when that side was held over and 

 parallel to the needle. On leaving the face ab c, the electric 

 tide swept the general surface of the metal, flowing in various 

 directions, and returning by numerous windings to the point of 

 heat. By this distribution, and consequent attenuated state 

 of the electric force, the thermo-magnetic energies were com- 

 paratively very feeble on every part of the metal excepting the 

 face abc; on which alone they were displayed with prompti- 

 tude and regularity. 



93. When the point of heat was at b, the whole of the tri- 

 angular face became again magnetic, displaying phaenomena 

 of precisely the same character as those which had been eli- 

 cited when the point a was excited ; and the distribution of 

 the electric forces had again a decided reference to the point 

 of heat; emanating therefrom, and flowing with as great an 

 uniformity over the surface of the fracture as if it had been 

 a conductor from the copper to the zinc of a single galvanic 

 pair. The arrows in fig. 17. will indicate the distribution of 

 the electric force over the surface of the lamellated fracture 

 when the point of heat was at b. 



94. When the fracture was heated at c, the thermo-mag- 

 netic phaenomena were again displayed with very nice pre- 

 cision and uniformity on that particular face of the metal ; 

 whilst on the other parts of the surface they were confused 

 and irregular; showing that the electric forces on those pails 

 •were dispersed in various directions, and enfeebled by their 

 separation, or by their returning to the point of heat, through 

 the body or general mass of the metal. Fig. 18, will show the 

 direction of the electric tide on the face abc^ when the point 

 c was excited by the flame of a spirit-lamp. 



Remarks. 



95. The uniformity displayed in the results of the preced- 

 ing class of ex|)uriments confers on them a very interesting 

 character in these investigations. In connexion with those on 



rtguliir 



