228 



M. Dvorak on Acoustic Repulsion. 



17 millims.; and its opening was placed in front of the centre 

 of a vibrating segment, or ventre. 



2. The Acoustic Mill. — A continuous rotation is easily ob- 

 tained, on the principle of the acoustic repulsion of resonators, 

 by fastening four very light paper or glass resonators upon 

 two wooden rods, op, qr (fig. 3), crossing at right angles, 

 and balanced on a glass cap ; all the openings of the resona- 

 tors fronting one side in the direction of tangents. The whole 

 apparatus is placed before 

 the opening, K, of the reso- Fig. 3. 



nating box and fork, in the 

 manner indicated in fig. 3. 

 The open end a of resonator 

 1 is repelled from K ; the 

 closed end b of resonator 2 

 is attracted : but in general 

 this attraction does not in- 

 crease the rapidity of rota- 

 tion, because it counteracts 

 rotation the moment the re- 

 sonator (2) has changed its 

 position about 45°. It is 

 therefore not possible to ob- 

 tain continuous rotation by 

 means of acoustic attraction, 

 as I have shown by numerous experiments*. The resonator 



(1) continues to move by reason of its inertia, and resonator 



(2) takes its place, being in turn repelled, and so on. 



A very rapid rotation is obtained by using a large Kundt's 

 tube and placing a small acoustic mill before its open end. 



The glass tube (Kundt's), which vibrates longitudinally and 

 produces the tone, is fastened to a heavy table, and protrudes 

 only a short distance through the cork into the glass tube, 

 placed upon a separate table so that its open end projects 

 somewhat beyond the edge of the latter. The length of the 

 rod was 127 centims., the diameter 27 millims. ; the half wave- 



length of its note, ^, equals 10J centims. 



The length of the 



tube was 45 centims. ; the length of the vibrating column of 

 air, corrected for the open end, was 3 « -f- j ; the inner dia- 

 meter was 5 centims. 



* Instead of the resonators (fig. 3) I used vertical paper vanes, varying 

 e curvature, without achieving any results, notwithstanding the fact that 

 there was a pretty strong acoustic attraction for each separate vane. 



