﻿K. H. Shellbach on Acoustic Repulsion and Attraction. 421 



becomes too sensitive to air-currents, so as to be useless for these 

 experiments. An ordinary small magnetic needle, carrying on 

 the one pole a paper disk of 4 centimetres diameter and on the 

 other a small wax ball as counterpoise, is distinctly attracted by 

 a vibrating tuning-fork from a distance of more than 1 deci- 

 metre. 



The effect of sound-vibrations may be also detected on light 

 and even somewhat heavy pendula. A ball weighing 3 kilo- 

 grammes hanging from a thread 2 metres in length could be 

 set in visible vibration when the fork was stroked with the bow 

 always isochronously with the pendulum's vibration. It was 

 even possible in this manner to set in vibration an iron disk 

 weighing 10 kilogrammes which could swing on a string 3 metres 

 long fastened to an iron beam in the wall. 



Quite recent experiments of mine have thrown somewhat 

 more light on these phenomena. Two sheets of thin plate glass, 

 2 centims. long and 15 centims. broad, were fastened on to two 

 stands and brought into the same vertical plane, so that a ver- 

 tical slit 15 millims. wide was left between them. At a distance 

 of 1 decimetre from the sheets of glass was placed the above- 

 mentioned sounding-box with the plane of its mouth parallel to 

 the sheets. If now a candle-name was placed very near to the 

 slit, between the slit and the box, it was as strongly attracted 

 (drawn away from the slit) as it would otherwise have been re- 

 pelled. If, however, the flame was placed on the other side of 

 the box* rather near to the slit, it was repelled so as to be 

 driven away again from the slit. This experiment explains at 

 once the phenomenon presented by the current of sal-ammoniac. 

 The rising column of vapour represents the slit, and the sur- 

 rounding air corresponds with the rigid glass plate. Hence the 

 stream is divided into two divergent branches as above de- 

 scribed. It was to be expected that solid bodies might also in 

 the same way be repelled by the sonorous vibrations in place of 

 being attracted, as hitherto exclusively observed. In fact strips 

 of stout cardboard, 15 millims. broad and 50 millims. long, are 

 strongly repelled when they are placed at a distance of 5 to 8 

 millims. from the slit, between the plates and the box. Placed 

 on the other side of the slit, they are attracted. The cardboard 

 strips, therefore, approach the slit in both cases. 



By the help of such a slit, which may be made by employing 

 tinplate strips, the attractions and repulsions caused by sonorous 

 vibrations may be produced at distances far greater than those 

 hitherto noticed. They depend chiefly on differences in the. 



* "Jenseits des Kastchens." No figure is given ; from the context I pre- 

 sume the expression should be "jenseits des Spaltes," on the side of the 

 slit away from the box. — E. G. 



Phil. Mag. S. 4. Vol. 41. No. 275. June 1871. 2 F 



