Homogeneous Bodies ; "with illustrative Experiments. 1 1 



edges of curvilinear frames as close as possible to the mag- 

 netic needle, I cast several into an elliptical form ; the diameters 

 of each of which were nearly as to 3 to 1. Every one of these 

 frames became magnetic by heating at various points, in the 

 manner already described ; and the thermo-magnetic energies 

 were as promptly displayed in every part of the curve by heat- 

 ing an individual point, as in any thermo-magnetic circuit 

 whatever. 



41. I must not omit to mention a very extraordinary cir- 

 cumstance which occurred whilst varying the experiments 

 with one of those elliptical frames ; because the same cause 

 frequently produces very singular changes in the thermo- 

 magnetic character of curvilinear and other frames of bis- 

 muth. 



42. Having proceeded in the usual way (11), I succeeded 

 in detecting several active points in the ellipse. The direc- 

 tions of the various currents which were excited by heating 

 those points are indicated by the arrows in fig. 8 ; the 

 arrow always pointing in the direction of the current when 

 any point was healed within its length. This done, I made a 

 deep curved notch in the inner side of the rim at the point dy 

 fig. 9, by means of the convex side of a half-round file. This 

 small alteration in the edge of the frame caused such a won- 

 derful difference in the activity of its thermo-magnetism as to 

 surpass anything I had hitherto observed. The magnetic 

 energies not only became very much exalted, but in several 

 parts of the frame had comj)letely changed their direction. 

 When heated at the points o, ovf, the deflection of the needle 

 was at least three times greater than before the notch was 

 made. When those two points were heated at the same time, 

 the conspiring magnetic energies thus excited, deflected the 

 needle 50° at the first impulse; and by changing the direction 

 of the frame to promote the deflections, the needle was soon 

 made to sweep an arc of more than 200° ; and by following 

 the oscillating needle with the edge of the frame, the former 

 was driven, by the thermo-magnetic forces of the latter, several 

 times cjuite round the whole circle*. 



Remarks 



• My motive for making this deep notch in the side of the frame, was 

 that of checking the progress of the heat in one direction more than 

 another, when applied to either side of it, — an object which I had in view 

 from the commencement of tiiese experiments, and wiiicii I liad in vain 

 attempted to accomphsh by means of angnhir points (l."5) ; and from fre- 

 quent disa|)pointments !)y the apparently fbrtuitons results in tlic [)reced- 

 ing, and many otiicr cx|)eriments which I have not mentioned, I had lost 

 all li()[)e of arriving at anything like interposition, in any other way than 

 that of modifying tlie crystallization of the metal. Tiie results of this ex- 

 periment, liowevcr, were very singular; and I have since found, that 

 Q 2 similar 



