Homogeneous Bodies; "with illustrative Experiments. 9 



than in either of the two former ; particularly when heated 

 opposite to the arrows i i. The thermo-magnetic powers of 

 A and B, however, when those rectangles were heated at two 

 or more conspiring active points, would frequently deflect the 

 needle over an arc of 30° or 40° by the first impulse. 



35. The rectangle A was so exceedingly sensible by the 

 slightest inequalities of temperature in its various parts, that 

 the heat imparted by the finger and thumb by which it was 

 held, would excite an electric current of sufficient energy 

 to deflect the needle 4" or 5°. Indeed, the temperature of 

 the metal was very seldom so far equalized as to render its 

 electric powers completely inert. The natural changes in the 

 temperature of the atmosphere seem to be almost sufficient 

 to perpetuate electric currents, without any artificial change 

 whatever. 



Fourth Class of Experiments. 



36. As it had appeared from the preceding experiments, 

 that considerable thermo-magnetic action was elicited by bis- 

 muth when cast into the shape of rectangular frames, I was 

 desirous to ascertain if those powers were communicated to it 

 by employing it in that particular shape ; or if it would still 

 display thermo-magnetic phiEUomena when cast into other 

 forms. To set this question at rest, I cast several circular 

 rings, or frames of bismuth. The exterior diameter of each 

 ring was 4- inches, and the interior diameter 3 "5, leaving the 

 metal '25 inch thick. They were cast with the plane of the 

 mould liorizontal, and open at the upper surface. The height 

 of each ring when in that position was about "4 inch. 



37. By applying the flame of a spirit-lamp to various parts 

 of each ring, and immediately presenting the metal to the 

 compass-needle in precisely the same way as had been done 

 with the rectangles (11.), several active points in each ring 

 were soon discovered, the energies of which were continuous 

 throughout eveiy part of the circular frame, putting the whole 

 circle into a state of thermo-magnetic activity. iSeveral in- 

 active or Jientral points were also found in these rings, by 

 heating which, no perceptible influence was exercised on the 

 needle by bringing the metal close to it. These results left no 

 (juestion remaining as to the magnetic power being innate and 

 natural to the metal; and not comnuniicatcd to it by its assu- 

 ming any particular form. It nuist certainly be acknowletlgcd, 

 however, that the rings have never disphiyed the thermo- 

 magnetic energies in so exalted a degree as I have observed 

 in tlie rectangles; but this difference ol" energy may possibly 

 be attributable to the difference in tlic extent of surface which 



N.S. Vol. 10. No. 5.';. Jiih/ 1831. C can 



