EULOGY OA' AMPERE. 137 



honored amougstmeii. I will try to give a clear and exact idea of this 

 most importiiut discovery. 



The voltaic pile is termiuated at its extremities, or, if you prefer as 

 an expression more suitable, at its two poles by two dissimilar metals. 

 Let us suppose, for example, the elemeuts of this wonderful apparatus 

 to be copper aud zinc ; if the copper is at one of the poles the zinc 

 will inevitably be at the other. The battery, with the exception of some 

 .shght traces of tension, is, or at least seems to be, completely inert as long 

 as the extreme poles are not put into communication by means of a sub- 

 stance conductive of electricity. A metallic wire is generally used to 

 connect the two poles of the battery, or, which amounts to the same 

 thing, to put the app aratns in action. This wire is then called the con- 

 junctive wire. 



A current of electricity passes along the whole length of the con- 

 ductor, and circulates uninterruptedly through the closed circuit, result- 

 ing from the union of the wire and the battery. If the battery is very 

 powerful, the current will be equally so. 



Physicists had for a long time known how to impart to an insulated 

 inetallic wire a large quantity of electricity in repose, or electricity of ten- 

 sion, as it is calledin treatises on physics; they also know how to trans- 

 mit electricity along wires not insulated in very large quantities ; but in 

 this case the passage was sudden and instantaneous. The first means 

 of combining intensity with duration in currents of electricity is fur- 

 nished by the galvanic battery, with which a discharge, more powerful 

 than could be produced by the largest ancient machines for the millionth 

 part of a second, is here given for hours together. Does the con- 

 junctive wire, the wire along which a quantity of electncity passes un- 

 hiterrupiedly, acquire, in consequence of this movement, any new prop- 

 i-rties ? To this question the experiment of CErsted replies afSrmatively 

 in the most striking manner. 



Let us place a wire of a certain length, of copper, silver, platiua, or 

 any other metal without appreciable magnetic action, above a horizontal 

 compass, awii parallel to its needle. The presence of the wire will have 

 no etfect. Make no change in the first arrangement, but join, either 

 directly or by intermediary long or short wires, the two extremities of 

 the parallel wire to the two poles of a voltaic pile ; or in this way let 

 us transform the insulated wire into a conjunctive wire, along which a 

 permanent current of electricity passes, and at that very instant the 

 needle of the compass will change its direction ; if the battery be feeble 

 the deviation will be inconsiderable ; but if the battery be very strong, 

 iiotwithstanding the action of the earth, the magnetic needle will form 

 iiu angle of nearly 90^ with its natural position. 



I have supposed the conducting wire above the magnetic needle, 

 placed heloic the phenomenon would be the same with regard to quantity, 

 qut exactly opposite as to the direction of the deviation. The conjunc- 

 tive ^ire above would impel the north pule of tlie needle toward the 



