[ 20.3 ] 



XXXIII. On the Action of the Voltaic Pile upon the Magnetic 

 Needle. By M. Boisgkraud Jim. 



{Read in the Jcadetni/ oj Sciences, 9th Nov. IS20.) 



1. WAS witness in the sitting of the 1 1th September last, to some 

 experiments relative to the action of the pile on the magnetic 

 needle, which were repeated by AI. Arago, and of which M. CErsted 

 is the inventor. These newly observed phenomena inspired me 

 witli a lively interest ; I hastened to renew the experiments, and 

 saw my attempt crowned with success. I did not stop at these 

 first attempts; I made new trials, in which 1 obtained results 

 which appeared to me interesting, and which may perhaps assist 

 ill explaining this sort of phenomena. I shall confine myself to 

 reporting those which I conceive to be new. 



I made use of a Galvanic trough of tvventy pairs of the old 

 construction, and of little power. The conducting wire was com- 

 posed of tu'o wires of platina of small diameter ; they communi- 

 cated with the poles of the pile, by means of brass wires of a dia- 

 meter more considerable. I endeavoured to increase the effects 

 of my first pile, by uniting it to a second exactly the same, in 

 such a manner as to form a battery. This arrangement of the 

 apparatus gave me occasion to ascertain that the metallic arc 

 which joined the extreme poles, was not the only one susceptible 

 of making the needle deviate; the intermediary arc, which united 

 one of the piles to the other, produced the same effect, and ob- 

 served the same laws. I was even able to approximate the ef- 

 fects of the two arcs; and according as they tended, by their re- 

 spective positions, to produce a deviation in the same or in an 

 opposite direction, the effects were augmented or diminished. 



The 7iature of the conductors in these experiments appeared 

 to me to have a great influence. Thus, a simple leaf of paper 

 dipped in the liquid of tlie troughs of the pile sufficed to diminish 

 the effect considerablv, when it was interposed between the con- 

 ducting wires of my apparatus; a short piece of charcoal, partly 

 dipped in water, destroyed it entirely *. 



The following, is in this respect, a fact remarkable enough. 

 Having placed the magnetic needle under the intermediary arc 

 in such a manner that a strong deviation was produced when I 

 made the two extreme poles communicate by a metallic arc, it 

 was not so when I established the communication with my two 

 hands: however, I experienced a shock rendered the niore dis- 



• Some experiments since made by M. Ampere, with an apparatus of 

 •mall power, jirovcd that charcoal (especially if incandescent) does not 

 •iitiicly dejtroy the effects. Water churgcd with acid produces the same 

 effect. 



C e 2 agreeable 



