-32 M. Dvorak on Acoustic Repulsion. 



pipe, or fork, and a continuous rotation was exhibited. At 

 the same meeting this experiment was preceded by those on 

 the motions of silica-powder &c. in resonators. 



On the 8th of July, 1876,, there appeared in the ' Scientific 

 American ' a report of this meeting of the Academy, in which 

 my experiments on Acoustic Repulsion are thus referred to : — 



" In the next place, Professor Mayer exhibited an apparatus 

 constructed by him to produce motion by means of sound- 

 pulses. Four glass resonators on cross-arms were suspended 

 by means of a string. On sounding an organ-pipe in tune 

 with the resonators and bringing it opposite the mouth of one 

 of them, the resonator was repelled and the apparatus com- 

 menced to rotate. This experiment was the more striking 

 from the fact that, so far from any current of air proceeding 

 out of the mouth of the organ-pipe, the air is actually sucked 

 in, as may be rendered visible by means of smoke from a cigar. 

 The smoke is carried up the pipe even when the latter is closed 

 at the top with cotton wool so as to smother the sound. On 

 substituting disks of cardboard for the resonators, they were 

 drawn up to the mouth of the organ-pipe with considerable 

 force. When fine silica-powder was placed in the resonators, 

 it was thrown into violent motion on sounding the pipe." 



In the same month (July 1876) Dr. Pudolph Konig visited 

 me, and I exhibited the same experiments before him. 



The discovery of the acoustic repulsion of resonators and 

 the invention of the sound-mill were made independently by 

 Professor Dvorak and myself. It is another instance of men, 

 even so far distant as Agram and Hoboken, led into the same 

 path of research by the natural growth of science. 



Dimensions of the resonators and reaction- wheels used, in 

 millimetres : — 



(1) Fork C, of 128 vibrations. Glass resonator of form E 

 (fig. 1), a b equalled 90 ; h i, 25 ; hk, 20; hf, 33 ; fg, 8. Its 

 weight, together with its leaden counterpoise, was 70 grams. 



(2) Fork A, 435 vibrations per second. (a) The glass 

 resonator used in the experiment represented in fig. 2, and to 

 show the current of air bv means of smoke, was of the form D 

 (fig. 1) : ab equalled 58 ; hf, 22 ; fg, 10. (b) The glass 

 resonators of the acoustic mill were of the form D : a b equalled 

 34 ; hf, 12 ; fg, 3. The length of the arms from the middle 

 of the glass cap to the middle of the resonator was 52 millims. 

 The weight of the whole wheel was 23 grams, (c) Paper re- 

 sonators of the acoustic mill (fig. 3) were of the form A (fig. 1): 

 a b equalled 34 ; c d, 50 ; hf, 6 ; fg, 9. The length of the 

 arms was 65 millims., the weight of the whole wheel 9 grams. 



