28 M. Dvorék—Acoustic Repulsion. 
motions of a silica powder and films of soap-bubbles 
placed at various points in resonators of different forms. 
first smbliontaih of these results was on May 22d, 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 pipe, or fork, and a continuous 
rotation ssice exhibited. At the same meeting this experiment 
was pre y those on the motions of silica powder, etc., 
in cman 
constructed by h ce motion ns of soun 
iegiee Four sree resonators on cross arms were suspended 
means of a string. On sounding an organ-pipe in tune 
with the omucnaiies 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 mt 
out of the mouth of the organ-pipe, a este ay poras y pelea 
in, as may be rendered visible by m from a 
cigar. The smoke is carried up the ea even ides iC latter 
= closed at the top with cotton wool so as to smother the 
und. On substituting disks of cardboard for the resonators, 
hie were drawn up to the mouth of the organ-pipe with con- 
siderable force. hen fine silica powder was placed in the 
resonators, it was thrown into violent motion on sounding the 
pi 
In the same month, July, 1876, Dr. Rudolph Kénig 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 ms the natural growth of science. 
‘Dimensions of the resonators and reaction-wheels used, in 
millimeters: (a) "ork se of 128 vibrations. Glass resonator of 
form E, fig. 1, a a 90; hi 25; hk20; a th Its 
aie a together with its leaded Crete was 7 
(2) F ork A , 435 (vibrations per seco ofa: Phe ion 
resonator used in the experiment ent in fig. 2, and to 
