﻿* 



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



densities and tensions of the masses of air upon which the vi- 

 brations act. When such differences exist only to a small de- 

 gree (as, for instance, is the case with a very slowly ascending 

 column of sal-ammoniac or of phosphorous acid rising from a 

 fragment of phosphorus), the action of the sound- vibration is not 

 sensible; it is just possible to perceive that, in the immediate 

 neighbourhood of the phosphorus, a thicker mass of phosphorous 

 acid is developed at every beat of the tuning-fork. 



I am not at present able further to pursue these experiments, 

 which may be extended greatly ; and I should be very glad if 

 they were taken up by those physicists who have chiefly occu- 

 pied themselves with acoustic investigations. 



In conclusion, I must mention that as early as 1834 M. 

 Guyot noticed the attraction which light bodies suffer from a 

 vibrating tuning-fork. He adds that this action extends to a 

 distance of 9 lines. These observations are quite similar to 

 those subsequently made by Mr. Guthrie*. Although a short 

 notice of M. Guyot 5 s experiments is to be found in Pogg. Ann. 

 vol. xxxi. p. 640, 1 was not aware that such was the case till my at- 

 tention was directed to it by othersf . M. Guyot, in the Presse 

 Scientifique, 1861, torn. iii. pp. 246-257, attaches very general 

 theoretical reflections to his experiments, without, however, addu- 

 cing new experiments upon which to base them. 



My readers are already aware that Mr. Tyndall has already 

 made use of ammonia gas in his beautiful experiments on sen- 

 sitive flames. 



Acoustic Repulsion and Attraction. Ift/K.H. Shellbach J. No. 3. 



The sonorous vibrations of an elastic medium attract specifically 

 heavier bodies to the centre of disturbance and repel specifically 

 lighter ones. 



In order to establish this theorem experimentally, a small bal- 

 loon of goldbeater's skin, 2 decimetres in height, was filled with 

 atmospheric air and hung on a thread. A second similar bal- 

 loon filled with hydrogen was fastened by means of a thread to 

 a table so as to hinder it from rising. As soon as the above- 

 mentioned tuning-fork was set vibrating at a distance of 1 or 2 

 centims. from these balloons, the first approached the sounding- 

 box till it touched it, the second was violently repelled. This 

 repulsion also took place when the top of the balloon was fas- 



* Of course, when writing this, Herr Shellbach was only cognizant of 

 the abstract of my experiments in the Proceedings of the Royal Society, 

 No. 115, and was not aware of their scope. — F. G. 



t T also was ignorant of M. Guyot 's experiments and conclusions. A 

 translation of them forms Part I. of the present collection of papers on 

 the subject. — F. G. 



X Pogg, Ann. vol. cxl. St. 3, p. 495. 



