REPORT ON THERMO-ELECTRICITY. 303 
under the needle;—and that the magnetic action of metals 
unequally heated depends upon the form given them in casting; 
for which purpose masses of each metal, in the different forms 
of prisms, cylinders, and spheres both hollow and solid, w r ere 
heated successively in different points, and examined by apply¬ 
ing magnetic needles to their surfaces. From the different 
directions of the magnetism in cylinders of bismuth as they were 
cooled slowly or rapidly, he infers that there is some relation 
between the crystallization of metals and their magnetic pro¬ 
perties. I may observe that I had previously shown that no 
difference either in the nature or quantity of the deviation could 
be detected in bismuth under similar circumstances, when 
forming a circuit with copper wires, &c. ; the modification 
induced by slow or rapid crystallization is confined to the direc¬ 
tion of the currents in the bar itself; and since fluid mercury is 
capable of becoming a thermo-electric element, crystallization 
is evidently not a primary agent in thermo-electric excitation 
or conduction, however it may modify its progress. 
The latest experiments connected with this branch of the 
subject, are those of Mr. Sturgeon in 1831, on the thermo¬ 
electricity of homogeneous bodies, and the connexion between 
crystalline arrangement and thermo-electricity. The objects 
of his two papers appear to be to trace the directions of 
the magnetic currents in masses of metal, varying the form and 
the point of excitation; and so far they agree with those of 
Yelin. With these it appears that Mr. Sturgeon was not ac¬ 
quainted, as he says he is not aware that any experiments are 
yet before the public, illustrative of thermo-magnetic action in 
one solitary piece of metal. As a general result, it may be 
stated that, whether the mass of metal were in the form of a 
rectangular prism, a cylinder, or a cone, upon heating a point in 
the periphery of one extremity, the current proceeded longitu¬ 
dinally from the heated point on the same side of the axis, and 
returned on the other side, accompanied with transverse cur¬ 
rents passing in opposite directions nearly at right angles to the 
longitudinal ones. With a large rectangular plate of zinc, 
when the heat was applied at one of the angles, the electric 
current was in the direction of the diagonal advancing, and re¬ 
turned along the edges. In this and all similar experiments, it 
seems that the direction of the electricity to or from the heated 
point, depends upon some peculiarity in each metal, which re¬ 
mains to be discovered; but that the course of the currents 
afterwards, with reference to the figure of the mass, depends 
solely upon the figures; and I think may be accounted for, by 
considering the -whole as a congeries of wires, from which, ac- 
