20G On (he Action of I he Voltaic. Pile upon the Magnetic Needle. 



die point of tlie needle is in the vertical plane passing hv the con- 

 ducting wire, it remains in a state of repose. This eqnilibriun) is 

 fixed, every lime that in this position the conducting wire ap- 

 pears to exercise an attraction on the poles of the needle, and 

 nioveahlc, if it is directed in such a manner as to exercise a re- 

 pulsion. This retnavkahle jihanomenon seems to prove that the 

 conducting wire acts only the poles of the needle. 



The attractions and repulMons a*)ove mentioned, succeed in 

 certain cases in a manner which merits observation. The needle 

 of which I made use, was placed on the water in a glass stand, 

 in such a manner that, to observe what passed u'hen the conduct- 

 ing wire was under the needle, I plunged it in the water ; and 

 after having plunged it in the water, it came out to the right and 

 left of the needle before touching the edges of the glass. I then 

 drew some parallels to the meridian bv the two points where this 

 wire issued from the water. I divided the surfr-ce of the water 

 into three parts ; the one comprehended between the two wires, 

 and which I called interior ; the two others beyond them, or ex- 

 terior. Thus placed as indicated in the preceding table, every 

 time tlial" tiiere was attraction in the interior part, there was re- 

 pulsion in the exterior parts, and vice versa. For then the needle, 

 after having been repulsed in one of the divisions of water, passed 

 to that where it had attraction Ly a movement owing in part to 

 a declination, and more or less slow according to the distance 

 of the needle. Once drawn to the attractive side, it takes an 

 accelerated movement, which continues till its middle comes op- 

 posite to the conducting wiie. This middle point recedes slowly 

 iVom the wire. 1 believe that the impossibility of touching it 

 may be ascribed to a capillarv effect. 



It will be seen bv these latter experiments, that there is no equi- 

 librium for the needle subjected to the action of the conducting 

 wire, except when its middle point is of all the points the nearest 

 to the conductor. 



I believe that, according as the needle, after being repulsed in 

 one of the divisions of water, enters the other by the north or by 

 the south, it has -i greater tendency towards one part of the con- 

 ducting wire than the other ; but this law does not always hold. 

 This tendency of certain faces of the needle, and of the conducting 

 wire, to approximate, in preference to others which seem on the 

 contrary to repel, appears to me to have great influence in these 

 phaenomena. It seems to me also, that the results of forces which 

 produce these movements may be regarded as situated in a plane 

 perpendicular to the direction of the conducting wire. 



1 atteinpted, lastlv, a sort of experiment from which it is diffi- 

 cult to draw conclusions on account of their con^plexily. [Tiie 

 account of these experiments in our next.] 



XXXIV. No. 



