12 Mr. W. Sturgeon on the Thermo-magnctism of 



Remarks on the preceding Experiments. 



43. It would be needless (indeed almost endless) to de- 

 scribe all the peculiarities which have attended the numerous 

 repetitions of the preceding experiments ; and the variety of 

 circumstances under which I have cast rectangular, triangular, 

 and curvilinear frames of bismuth ; as the phfenomena already 

 described, with a i^vf summary remarks, will pourtray their 

 general character. 



I am not certain that any peculiar property is communi- 

 cated to bismuth by the magnetic process (23), or by the 

 position of the metal as regards the cardinal points, whilst 

 casting. I have frequently cast rectangles under these cix- 

 cumstances, but have not found more regularity in the display 

 of their thermo-magnetism than in those which were cast 

 under circumstances quite different. 



In general, small, and well-formed rectangles (17) (fig. 3.) 

 operate with much greater regularity, as regards the angles, 

 than those which are of larger dimensions (figs. 4, S, 6). But 

 it frequently happens that the energies of the latter are much 

 superior to those of the former. 



The currents, more frequently than otherwise, proceed in 

 opposite directions, when excited on different sides of an 

 angle. And in those cases where it happens otherwise, the 

 neutral point is situated almost close to the angle. 



The gate is invariably a neutral poitit when the mould is 

 not very hot at the time of casting, and more frequently than 

 otherwise in castings generally. 



The thermo- magnetic character of frames of bismuth, 

 whether a?ignlar or curvilinear, may be considerably modified 

 by removing, or partially removing, crystalline groups, or by 

 altering their forms. (41, 42 and note.) 



Every part of a continuous ring or rectangular frame of 



fimilar results frequently happen from the same cause : this however is not 

 always the case; it takes place most frequently in those frames which, 

 whilst whole, are not very active; and a neutral point ought to be se- 

 lected for the situation of the notch. I have frequently reduced parti- 

 cular parts of circular rims of bismuth with a hot iron, and sometimes 

 with the flame of a spirit-lamp, instead of a file, and with similar results. 



There is another method of exhibiting a very remarkable and nearly 

 allied property of thermo-magnetism, much more decidedly than by that 

 of filing,— by experiments which do not properly belong to this class, 

 although they were suggested by the results of the experiment last de- 

 scribed ; besides, there are impediments of which I must warn the reader, 

 before I can possibly describe the method of arriving at anything like suc- 

 cess. The circunistanccs, however, which I have called impediments, 

 emanate from the display of a very interesting class of phaEnomena, which 

 J shall presently describe. 



bismuth 



