138 EULOGY OX AMPERE. 



west; tbo deviatiou would be toward the east wheu, the conditions 

 being the same, the wire is below. It is necessary to remark here that 

 the wire preserves absolutely none of that deviating power the moment 

 it ceases to be a conducting wire, or to join the two poles of the battery. 

 It would indicate a total want of scientific perception not to understand 

 how extraordinary and important are the results I have just announced; 

 not to observe with surprise an imponderable liuid imparting for the 

 moment to the slender wire along which it passes, properties so powerful. 



These properties, studied in their specific characters, are not less 

 wonderful. 



Even a child knows it would be useless to try to turn a horizontal 

 lever around a pivot on which its center rests by pushing or pulling it 

 lengthways — I nn^an, following the line leading to the center of rota, 

 tion. The force must necessarily be transverse. The perpendicular to 

 the lengtli of the lever is, no nuitter in what direction, that which 

 requires the h^ast force to create a given movement. The experiment 

 of M. CErsted is directly opposed so these elementary rules of mechanics. 



Please then to remember, when the forces developed by the passage 

 of the electrical ciurent in each point of the conducting wire are found 

 to correspond vertically with the axis of the needle itself, either above 

 or below, the de^'iation is at its maximum. The needle remains at rest, 

 on the contrary, when the wire is presented to it in a direction nearly 

 perpendicular. 



Such is the strangeness of these facts that, in order to explain them, 

 various physicists have had recourse to a continued tlow of electrical 

 matter circulating round the conducting wire at right angles to it, and 

 producing the deviations of the needle by way of impulse. Tliis was 

 nothing less, on a small scale, than the famous vortices contrived by 

 Descartes to account for the general movement of the planets around 

 tJie sun. Thus a physical theory which had been abandoned for more 

 than two centui'ies was recalled by the discovery of CErsted. 



We have already mentioned the imi)ortant remaik of the celebrated 

 IHinish physicist, that the deviations of the needle of a horizontal 

 compass approach nearer and nearer 90 degrees in proportion to the 

 increase of the power of the battery during the connection of the tsvo 

 poles by the wire. Feeble batteries, on the contrary, produce only 

 scarcely sensible movements. AVhat is the part played by that myste- 

 rious power, seeming to reside in the arctic regions of the globe, to at- 

 tract magnetic bodies in a certain way, and repel others 1 AVhat part 

 does it perform in lessening the deviations vrhen the battery has little 

 power 1 



Ampere perceived the importance of this question at tJie very iirst 

 glance ; he saw it was not a mere nice and subtle refinement without 

 bearing; he understood that the solution of the problem would stamp 

 with characteristic features the forces brought into play by the experi- 

 ment of CErsted ; but how get rid of the attraction of the earth ; hov.. 



