168 An Account of some Electro-Magnetic Experiments ■ 
mony, and bent, as the figure (Fig. 7. Plate IV.) indicates. It 
was kept in close contact with the antimony by means of copper 
rings. This bar was laid in the direction of the magnetic meridian* 
A needle was placed on the antimony, as shewn in the figure, and 
the ends N and S of the bar were successively heated by a spirit- 
lamp. When the heat was thus applied to the south end S, 
the magnetic needle immediately, and strongly, deviated to the 
east. The extent of this deviation depends on the length, mo- 
bility, and strength of the needle. We have seen it as much as 
68°. When the heat spreads more uniformly through the me- 
tal, the deviation decreases, and the needle gradually returns to 
the magnetic meridian. 
Supposing the deviation to the east at its maximum, the lamp 
burning under the end S, facing the south, if then it be removed, 
and placed under the end N, the deviation to the east will de- 
crease, and it will change into a deviation to the west. 
In general, if the heat is applied under the north end of the 
bar, the needle will deviate to the west. 
2. It was then proposed to try whether cooling one end of 
the bar would produce the same effect as heating the other, and 
the apparatus was disposed as in Fig. 8. The end N was cooled 
in some frigorific mixture, whilst the end S was kept in the 
hand. Tlie needle deviated to the east , but, of course, not so 
strongly, as when the difference of temperature of the ends is 
produced by heating one of them. 
3. The apparatus was then replaced as in the first experiment, 
and both ends heated by a spirit-lamp. No deviation was ob- 
served; on removing the lamp under the south end, the devia- 
tion is to the west ; and on removing the lamp under the north 
end, that under the south remaining, the deviation is easterly. 
4. Two bars of antimony were used, and the needle placed 
between them, as shewn in Fig. 9- If both the ends N and N' 
were heated, the needle, placed in C, did not deviate. If the 
ends N and S' were heated, the needle deviated to the west. 
If S and N' were heated, the deviation is to the east. 
5. In this experiment, both ends of the bar of antimony were 
connected, not by copper, but by zinc, as in Fig. 7. The bent 
slip of zinc was fastened to the antimony by rings of the former 
metal. In order to make the experiment succeed, the oxide 
