EULOGY OX AMPERE. 143 



The problem appeared truly insoluble, wbeu our associate perceived 

 be could reach bis object by observing different conditions of equilib- 

 rium between conducting wires of certain forms placed one before the 

 other. The choice of these forms was the essential point; and it is here 

 the genius of Ampere displayed itself in the most marked manner. 



He first enveloped with silk two equal portions of tlie same conduct- 

 ing wire ; he bent this wire so that its two covered portions should be 

 in juxtaposition, and traversed from opposite sides by a current from 

 the same battery ; he was satisfied then that this system of two equal 

 but opposite currents exercised no power over the delicately sus- 

 pended conducting ^vire, and thus proved that the attiactive force of a 

 given electrical current is perfectly equal to the force of repulsion it 

 exercised when the direction of its course is mathematically inverted. 



Ampere then suspended a very moveable conducting wire, exactly 

 between two fixed conducting wires, which being traversed from the 

 same side by one and the same current ought to repel the intermediate 

 wire ; one of these fixed wires is straight, the other bent and twisted, 

 presenting a hundred small sinuosities. The communication necessary 

 to give play to the currents being established, the moveable intermediate 

 wire will stop exactly between the two fixed wires, and if moved from 

 its position will return itself to the same place. From this it follows that 

 if a straight connecting wire and a sinuous connecting wire, though 

 their unfolded lengths may be very different, exercise jiowers exactly 

 equal if they have extremities common to both. 



In a third experiment Ampere established undeniably that no closed 

 current whatever could cause a circular portion of connecting wire to 

 turn round an axis perpendicular to that one arc passing through its 

 center. 



Tlie fourth and last fundamental experiment of our associate is an 

 instance of equilibrium, involving three suspended circular circuits 

 whose centers are in a straight line, and whose radii are in a continuous 

 geometrical proportion. 



Our associate made use of those four laws to settle what he had al- 

 lowed to remain arbitrary in his analytical formula, conceived in the 

 most general terms imaginable to explain the mutual action of two in- 

 finitely small elements of two electrical currents. 



A skillful comparison of the general formula with the observation of 

 the four cases of equilibrium shows that the reciprocal action of the 

 elements of two currents is exercised in the direction of the line uniting 

 their centers ; that it depends on the mutual inclination of these ele- 

 ments, and that it varies in intensity in the inverse proportion of the 

 squares of the distances. 



Thanks to the profound researches of Ampere, the law, which governs 

 celestial movements, the law, extended by Coulomb to the phenomena 

 of electricity at rest or in tension, and then though with less certainty, 

 to magnetic phenomena, becomes one of the characteristic features of 



