including an EMmination of the Magnetic Field. 337 



magnet,, with the north pole to his right and the south pole to 

 his left, then when a current passed through the upper half o£ 

 the coil from the north to the south pole, that end of the bis- 

 muth which was turned towards the observer was deflected 

 towards the north pole ; and on reversing the current, the same 

 end was deflected towards the south pole. This seems entirely 

 to agree with the former experiment. When the bar hung equa- 

 torial between the excited poles, on the supposition of polarity 

 the opposite ends of all its horizontal diameters were oppositely 

 polarized. Fixing our attention on one of these diameters, and 

 supposing that end which faced the north pole of the magnet to 

 be gifted with south polarity^ and the end which faced the south 

 pole endowed with north polarity, we see that the deportment 

 to be inferred from this assumption is the same as that actually 

 exhibited ; for the deflection of a 'polarized diameter in the same 

 sense as a magnetic needle, is equivalent to the motion of the end 

 of the bar observed in the experiment. 



13. The following test, however, appears to be more refined 

 than any heretofore applied. Hitherto we have supposed the 

 helix so placed between the poles that the direction of its coils 

 was parallel to the line which united them ; let us now suppose 

 it turned 90° round, so that the axis of the helix and the line 

 joining the poles may coincide. In this position the planes of 

 the coils are parallel to the planes in which, according to the 

 theory of Ampere, the molecular currents of the magnet must 

 be supposed to move ; and we have it in our power to send a 

 current through the helix in the same direction as these mole- 

 cular currents, or in a direction opposed to them. Supposing 

 the bar first experimented with suspended within the coil and 

 occupying the axial position between the excited poles, a cur- 

 rent in the helix opposed to the molecular currents of the magnet 

 will, according to the views of the German philosophers before 

 named, be in the same direction as the currents evoked in the 

 bismuth : hence such a current ought to exert no deflecting in- 

 fluence upon the bar ; its tendency, on the contrary, must be to 

 make the bar more rigid in the axial position. A current, on 

 the contrary, whose direction is the same as that of the molecular 

 currents in the magnet, will be opposed to those evoked in the 

 bismuth ; and hence, under the influence of such a current, the 

 bar ought to be deflected. 



14. The bar at first experimented with was suspended freely 

 within the hehx, and permitted to come to rest in the axial posi- 

 tion. A current was sent through the helix in the same direc- 

 tion as the molecular currents of the magnet, but not the slight- 

 est deflection of the bar was perceptible ; when, however, the 

 current was sent through in the opposite direction, a very distinct 

 deflectiou WM the consequence : by interrupting th^ cu^yent 



