122 Mr. W. Sturgeon on the Thermo- Magnetism of 



by the direction of the electric forces, and those forces again 

 by the distribution of heat, the situations of the dotted lines 

 dn, d n, will also vary with the circumstances of heat. 



111. When one of the ends ad, fig. 20. of the rectangular 

 mass is uniformly heated, the distribution of the electric 

 forces will be indicated by the arrows in that figure. Here 

 again, it will be observed, that the electric forces are projected 



Ji'on the heated end into the area of the plate, and by re- 

 curving sweeps, return to that end again along the parallel 

 margins of the metal. In this case, the neutral lines, and lines 

 of greatest eneygy, are parallel to each other, and also parallel 

 to the sides ah, dc oi the rectangular plane. 



112. As a similar distribution of the electric forces to that 

 represented by fig. 19. is uniformly elicited by heating any 

 of the angles separately, the same system of arrows will serve 

 to illustrate that disti'ibution, to whatever angle heat may be 

 applied. If, for instance, the angle a were to be heated, the 

 points of the straight arrows dc,da, would then be directed 

 to a, or towards the point of heat; whilst the feathered end 

 of the former would be directed towards b, and that of the 

 latter towards the angle d. The central or diagonal arrow 

 would be directed from the angle a to the angle c ; and in 

 the same way the system of arrows may be considered to be 

 situated with respect to any other heated angle. The system 

 of arrows in fig. 20. will also apply to either of the ends of 

 the metal when uniformly heated between the angles. 



113. As both faces of the zinc exhibited thermo-mag- 

 netism of the same character in all the preceding experiments, 

 whatever has been stated concerning those experiments will 

 equally apply to both sides, or flat faces of the metal, and 

 I imagine to all similar masses of zinc. I must here observe, 

 that the electric forces very seldom reach to the cold end of 

 the mass, but approximate thereto in proportion to the ad- 

 vances of heat. They are the most powerful near to the 

 heated point, and become more and more languid as they 

 recede from it, till at length their energies are entirely lost 

 in the more remote parts of the metal. 



114. Experiments with Masses of' Coppei: — Copper is one 

 of those metals, the thermo-magnetic energies of which are 

 not very easily detected in separate homogeneous masses, un- 

 less they be of large dimensions. The most satisfactory re- 

 sults I have ever obtained from experiments on this metal 

 were elicited by a rectangular mass, about two inches thick, 

 and weighing about 95 pounds. This huge piece of copper, 

 which by the interest of Mr. Marsh I was permitted to ex- 

 amine, belongs to the Royal Arsenal. The experiments were 



made 



