( 'J-^ ) 



the lader, the !?iiino dexialioiis were iiolicecl as when nioviiig (he 

 hmnaii hand. 



x\lso these deflections changed only little when the metal disk was 

 moved, after having been charged by a sloi-age-cell to a ]»()tential of 

 -{- 2 or — 2. 



The idea tiial the strange phenomenon had to be ascribed to 

 currents in the <air which wonld generate electricity i>y friction, had 

 to be rejected at once, as soon as, by mt^ans of a pair of bellows, 

 a powerful air-current had been directed against the resistance-l>o\ 

 without the wire showing the least motion. But in the end the 

 explanation appeared to l)e ^ery simple. The ebonite plate of the 

 resistance-box has a certain charge and the hues of electric force 

 bend from the ebonite to the metal plugs. As soon as a conductor 

 now approaches, the lines of force are displaced and thus electricity 

 is moved from the metal through the galvanon»cter to the earth. 



That this is the real explanation could be easily shown by rubbing 

 the ebonite of the resistance-box ami so charging it to a higher 

 potential. When this Avas done the deviations became many times 

 Uxrger. 



An interesting proof of the usefidness of the wire-galvanometer 

 as a sensitive instrument which at the same time is quick in its 

 indicatiojis, is atforded by the ease and accuracy with which it 

 registers sounds. 



When a Sikmkns' telephone is connected with the galvanometer, 

 the sound-vibrations tallijig on the plate of the telei)hone will send 

 induced currents through the wire, by wiiich this latter will be moved. 



As soon as a tone of arbitrary pitch is made to sound against 

 the telephone with constant intensity, the image of the wire broadens 

 in a curious way. In the bright field the narrow, black image is 

 broadened to a band of several centimetres breadth, Avhich has a 

 light grey tint and whose appearance in the field is feebler as it is 

 broader. The middle of the grey band always corresponds to the 

 image of the quartz-thread in rest. The margins have a somewhat 

 darker delineation than the rest of the band. 



This appearance is entirely explained by the circumstance that the 

 wire executes regular, rapid vibrations of the same rhythm as the 

 sound-vibrations striking the telephone. 



One peculiarity has still to be mentioned. If a sound like a or o 

 is sung against the telephonc'plate, one sees the grey band divided 

 into parts. Symmetrically with respect to the middle of the image, 

 within its real margins something like secondary and tertiary margins 



