between Light and Electricity. 239 



rather if they act upon each other so as to modify their effects, 

 only in the part where they run parallel across a given con- 

 ductor, and not in the other parts of the same conductor. 

 For this purpose I wished to try to make two or more elec- 

 tric currents pass through the same wire of a galvanometer. 

 In order to do this, I fixed to one of the ends of the wire an 

 oblong plate of lead dipping in a cup of water, and in another 

 cup, I put a secdnd similar plate, connected with the other 

 end of the wire. A strip of lead which on one side communi- 

 cated with the positive pole of a Voltaic apparatus of 28 pair, 

 dipped in one of the cups, and in the other was placed the 

 extremity of a second strip of the same metal, communicating 

 with the negative pole of the same battery. The result was a 

 deviation of 20 degrees. The circuit being broken without de- 

 ranging, for this purpose, the plates of lead, I tried in a similar 

 manner the effect of a second battery of 25 couplet. I obtained 

 a deviation of 25 degrees. T did not then suspend the circula- 

 tion, and, when the needle had ceased to oscillate, the deviation 

 was 6 degrees. In order to be certain that the battery of 

 25 pairs still produced the same effect, although the electricity 

 of the apparatus of 50 pairs had already crossed the wire of 

 the galvanometer, I turned the box of the galvanometer in 

 such a manner that the needle still corresponded with the zero 

 of the scale ; I then restored the circuit in the apparatus of 

 25 pair, and the needle deviated exactly 20 degrees as before. 



In this experiment, the two currents followed the wire of the 

 galvanometer in the same direction. I had made them also 

 pass through in a contrary direction ; and the results present- 

 ed no difference except in the species of deviation ; it was now 

 west instead of east. 



Having caused the wire of the galvanometer to be passed 

 through by electric currents of four batteries of five pairs each, 

 that of twenty-five pairs again produced the same effect. 



11. In all these experiments I have used the galvanometer 

 as the instrument which would most easily show minute dif- 

 ferences of electric efifects. I have not, however, neglected the 

 other effects produced by the battery, the tastes, the shocks, 

 the electric tensions, &c. &c. but I could never perceive any 

 difference between the effects obtained by an electric current 



