Electro-Magnetic Experiments. 383 
experiments from 56° Farenheit, to about 95°, by the warmth 
of the hand, and in the second from 56° to 212° by a spirit lamp, 
I applied it instantly to its fellow at 56°, both being connected 
with the galvanometer, and noticed at each the number of degrees 
through which the needle moved in four seconds. I used equal 
times that the motion whether uniform or accelerated might be 
in proportion to the force. I found that the result varied in 
some degree with the varying circumstances of each experiment ; 
some of the causes of these fluctuations were ascertained, but 
others could not be detected. Perhaps they were produced by 
the various points which happened in each instance, to be in con- 
tact. I found that the electricity passed in some metals through 
the rupture with the heat and in others in opposition to it. The 
former metals may be called as by Prof. Emmet positive and the lat- 
ter negative. For conciseness, the terms cotncidence and “ opposi- 
tion” may be used. ‘To show how much these experiments may be 
varied by circumstances, I will state the particulars of those which I 
made with silver. Having procured a silver wire, one sixteenth of 
an inch in diameter, and two feet long, drawn without annealing,—I 
cut it in two and connected the other ends with the galvanometer, 
warmed one of the cut ends by holding it in my hands and laid it 
upon the other, the needle turned three degrees in four seconds in 
such direction as indicated a negative current. After letting it cool 
I warmed the other end and applied it in the same manner to its fel- 
low. Although the course of heat had been reversed the needle 
still turned in the same direction, indicating a positive current of the 
same force as the negative one! here it seemed the electricity passed 
in the same direction along the wires whether the one or the other was 
heated. After heating the ends of them to redness over the spirit 
lamp I let them cool and heating one to 212° Far. applied it to the 
other, and letting them cool again, reversed the experiment by heat- 
ing and applying the other. Both of these experiments showed a 
negative current but in one it was scarcely perceptible while in the 
other it was 12° in four seconds. ‘This change produced by heating 
the ends of wires gave me the the hint to anneax them throughout. 
I did so, and then found the results to be rational and uniform. 
They were positive four degrees in four seconds by hand heat, and 
sixteen degrees in four seconds by boiling heat. ‘The same result was 
obtained by reversing. It seems by the results of these experiments 
that the metals must not only be of proper lengths without joints or 
