223 Intelligence and Miscellaneous Articles. 



ON THE INFLUENCE EXERCISED ON THE MAGNETIC NEEDLE BY 

 MUSICAL STRINGS IN A STATE OF RESONANCE. BY DR. H. 

 REINSCH*. 



(Extract.) 



". . . . The interesting experiment of the rotating copper disc in- 

 stituted by Arago, led me to examine the effect upon the magnetic 

 needle of a vibrating string covered with copper wire. For this 

 purpose I stretched a copper-covered string upon a violin, and sus- 

 pended above it a light magnetic needle by means of a filament of 

 cocoon-silk. The needle that I made use of was a sewing-needle, 

 about an inch and a half long. The direction of the string was made 

 to coincide exactly with the magnetic meridian, and the distance 

 between the string and the needle was about the twelfth of an 

 inch. 'I'he string was now thrown into the state of resonance by 

 means of a violin-bow, but the needle remained entirely motionless ; 

 on the contrary, it rather appeared that, after having been made to 

 oscillate purposely, it returned more rapidly to its normal direction 

 than if the string had been allowed to remain mute. Instead of 

 using a metal string I now had recourse to one of catgut, and sus- 

 pended the needle above an ordinary treble violin string, when the 

 first stroke of the bow was sufficient to impart a considerable deflec- 

 tion to the needle, and by five or six strokes in quick succession a 

 deflection amounting to 90° is easily produced. The purer the tone 

 is, and the greater the tension of the string, the more marked is the 

 deflection. 



" The various deflections, corresponding exactly with those brought 

 about by the galvanic current, are exhibited in the subjoined figure. 

 4 3 2 1 



A* 



w 



k ' 



n !e~--a 



jp Vc it Vt 



" The string, a b, is made fast at/; b r is the bridge of the violin ; 

 n the magnetic needle freely suspended ; s t indicate the stroke of 

 the bow, its direction being shown by the arrow-head. Immediately 

 that a stroke of the bow is given near the bridge in the direction 

 shown in the figure, the needle is deflected westward, as seen at 1 ; 

 on giving the stroke in the contrary direction, as shown at 2, the 

 needle is deflected in an easterly direction ; on giving the strokes 

 at the south end of the needle, the deflections take place in exactly 

 opposite directions to those brought about by the strokes given at 

 the north end of the needle, as seen at 3 and 4." 



* Ueber den Einfivss tonender Saiten auf die Magnetmidel, von Dr. H. 

 Reinsch. Communicated by W. G. Lettsom, Esq. 



