728 PROFESSOR THOMSON ON THE ELECTRO-DYNAMIC QUALITIES OF METALS. 
coil, without causing the slightest sensible current through the nickel, and 
serving also to convey a stream of cold water to maintain the lower parts of 
the two branches of the horse-shoe at as nearly as possible equal tempera- 
tures. 
AAA, india-rubber pipes to lead a stream of cold water through the coolers. 
C, magnetizing coil, wrapped on one of the copper coolers. 
E E, electrodes of magnetizing battery of twenty iron cells, charged with nitric 
acid, &c. 
F, commutator for interrupting and reversing the connexion between the mag- 
netizing battery and coil, or reversing the current. 
M M, mercury cups, in which the extremities of the nickel were immersed (mercury 
being both very convenient for the purpose, and the metal least thermo- 
electrically removed from nickel of all that have been tried by any experi- 
menter). 
m m, mercury electrodes joining copper galvanometer electrodes D D, at G G. 
K, commutator for interrupting and reversing the connexions of the galvanometer 
electrodes. 
Heat was applied at H H by means of a gas-lamp and blowpipe. A current from 
magnetized to unmagnetized through hot, was indicated by a considerable galva- 
nometer effect, which, by management of the galvanometer break, K, was readily 
directed to give oscillations of the needle through three or four degrees. 
The same conclusion had been indicated in several previous attempts, with various 
defects of arrangement remedied in the experiment just described. In this last expe- 
riment the result was made most manifest; and, being completely separated from all 
effects of induced currents (which were quite insensible), of electrical leakage, and 
