of Electro-Magnetism by Heat. 75 
purpose. Platina and iron are obviously unsuitable; and taking into con- 
sideration the fact of small wires being far more energetic than larger in 
proportion to their bulk, I believe no other arrangement of metals would 
be found so efficacious. 
The wire parallelogram AbcB, Fig. 12, deviates from right to left, or 
vice versa, accordingly as the north or south poles of the magnet are presented 
to it; its weight, together with that of the magnet, is rather less than seven 
grains. The apparatus, Fig. 13*, when heated by a Spirit lamp, exhibits 
a perpetual rotation, and is analogous to the instrument invented by Ampire 
for producing the same effect by galvanic excitation. 
* A small wire is soldered at d in the opposite direction to B, D,C to preserve the 
equilibrium ; notice of this was accidentally omitted in the plate. 
Kk 2 
