M. Dvorak on Acoustic Repulsion. 231 



The cone may be replaced Fig. 4. 



by a cylinder having the 

 width of the Kundt's tube, 

 open at the end turned to- 

 ward the latter, and closed 

 all but a small hole at the 

 end ; but the current is much 

 weaker; nevertheless it will 

 move a small wheel with ver- .^zi^^i^z^=z^zzzi^iz=rizzzi^r 

 tical paper vanes (fig, 4). 



In the experiments with the tuning-forks, it is essential 

 that the cone should vibrate to the same note as the fork ; 

 otherwise the current is too weak. For the fork A (of 435 

 vibrations) the openings of the cone have diameters of 82 and 

 3 millims., and its length is 373 millims. The opening at the 

 apex of the cone must be very small to obtain an appreciable 

 current. 



On conclusion of this investigation, Dr. K. Konig kindly 

 communicated to me that Mr. Alfred Mayer in New York 

 [Hoboken] had previously succeeded in producing continuous 

 rotation by means of sound. The communication was as fol- 

 lows : — " Professor A. M. Mayer showed me a very similar ex- 

 periment last summer (1876). He suspended by a thread two 

 large well-tuned flasks attached to a rod, and caused the whole 

 apparatus to revolve by means of a tuning-fork. I informed 

 him in consequence that you had previously demonstrated the 

 phenomena of repulsion in resonators; for he was not acquainted 

 with your paper* on acoustic attraction and repulsion." 



Note by Professor Alfred M. Mayer. — My connexion with 

 the discovery of the sound-mill is as follows : — 



In January 1876 I made the discovery (first reached by 

 theoretic deductions) that there was more pressure on the inner 

 surface of the bottom of a resounding cavity than on the outer 

 surface of the bottom, which touches the outer air. I subse- 

 quently proved the truth of this conclusion by experiments on 

 suspended resonators, and by observations on the motions of 

 precipitated silica powder and films of soap-bubbles placed at 

 various points in resonators of different forms. My first pub- 

 lication of these results was on May 22, 1876, on which day I 

 read a paper on this discovery before the New- York Academy 

 of Sciences, and exhibited before the members an apparatus 

 formed of two + arms of light wood, with a resonator attached 

 to each arm, as in fig. 3 of Professor Dvorak's paper. On 

 sounding an organ-pipe, or a fork on its resonant box, in tune 

 with these resonators, they were successively repelled from the 

 * Read before the Royal Academy of Sciences, Vienna, in 1875. 



