266 Scientific Intelligence, 



y 



cuiTcnt, Here fhen we liad an excited helix wliicli itself had no action 

 upon the magnets, and we were thus at liberty to examine the action of 

 a body placed within the helix and excited by it, undisturbed by the in- 

 fluence of the latter. The helix was twelve inches high, and a cylinder 

 of soft iron six inches long suspended horn, a string and passing over a 

 pulley could be raised or lowered within the helix. When it was so far 

 sunk that its lower end rested upon the table, the upper end found itself 

 between the poles N S, attracting one of them and repelling the other, 

 and consequently deflecting the astatic system in a certain direction. 

 When the cylinder was raised so that the upper end was at the level of 

 the top of the helix, its lower end was between the poles N'S'; and a 

 deflection opposed in direction to the former one was the immediate con- 

 sequence. To render these deflections more visible to the audience, a 

 mirror m, was attached to the system of magnets ; a beam of hght 

 thrown upon the mirror was reflected and projected as a bright disk 

 against the wall of the theatre ; the distance of this image from the mir- 

 ror being considerable, and its angular motion double that of the latter, 

 a very slight motion of the magnet was sufficient to produce a displace- 

 ment of the image through several yards. This then is the principle of 

 the beautiful apparatus* by which the investigation now brought forward 

 was conducted. It is manifest that if a second helix be placed between 

 the poles S jS" with a cylinder within it, the action upon the astatic mag- 

 net may be exalted. This was the arrangement made use of in the actual 

 inquiry. Thus to intensify the feeble action, which it is here our object to 

 seek, we have in the first place neutralized the action of the earth upon 

 the magnets, by placing them astatically. Secondly, by making use of 

 two cylinders, and permitting them to act simitltaneously on the four 

 poles of the magnets, we have rendered the deflecting force four times 

 what it would be, supposing only a single pole to be used. Finally, the 

 whole apparatus was enclosed in a suitable case, which protected the 

 magnets from atmospheric currents, and the deflections were read off 

 through a glass plate in the case, by means of a telescope and scale 

 placed at a considerable distance from the instrument. 



A pair of bismuth cylinders was first examined. Sending a current 

 through the helices, and observing that the magnets swung perfectly free, 

 it was first arranged that the cyhnders within the helices had their cen- 

 tral points opposite to the poles of the magnets. All being at rest the 

 number on the scale marked by the cross wire of the telescope was 5V2. 

 The cylinders were then moved so that two ends were brought to bear 

 simultaneously upon the magnetic poles : the magnet moved promptly, 

 and after some oscillationsf came to rest at the number G12; thus mov- 

 ing frozn a smaller to a larger number. The otlier two ends of the bars 

 were next brought to bear upon the magnet : a prompt deflection was 

 the consequence, and the final position of equilibrium was 526 ; the 

 movement being from a larger to a smaller number. We thus observe a 

 manifest polar action of the bismuth cylinders upon the magnet j one 

 pair of ends^doflecting it in one direction, and the other pair deflecting Jt 

 in the opposite direction* 



Devised hj Prof. W. "Weber, and constructed by M. Leyser, of Leipzig. 

 f To lessen these a copper damper was made use of. 



