230 M. Dvorak on Acoustic Repulsion. 



The excess of pressure as shown by a manometer at the node 

 is always less than the theoretical pressure, because in the 

 latter the air is not supposed to move from the node and to 

 equalize the pressure. Of course the excess of pressure at 

 the ventre is not equal to zero, as theory requires. Probably 

 the friction of the walls has much to do with these phenomena. 

 It may be expected from what has been said, that the air will 

 issue from the vessel in which it vibrates in stationary waves. 

 The manometer shows, in the first place, that the excess of pres- 

 sure is not equal to zero in the plane of the opening of a reso- 

 nator, because a portion of the air immediately in front of this 

 opening partakes of this stationary wave-motion, and because 

 there is always a small excess of pressure even in the ventre 

 of a stationary wave. There is no doubt that a partial equali- 

 zation of pressure takes place at the opening; experiments 

 show, furthermore, that there is a continuous exit of air, which, 

 as in Kundt's tube, is probably neutralized by a secondary 

 and contrary current. 



The exit of the air can easily be proved as follows : a sphe- 

 rical glass resonator is placed before the resonant base of a 

 tuning-fork; the resonator is filled with tobacco-smoke; strong 

 vibrations are given to the fork, when the smoke will be seen 

 to rush from the resonator. 



The current of air proceeding from a resonator is well shown 

 by means of a Chladni plate, by means of lycopodium, which 

 accumulates upon the ventres in little heaps when the plate is 

 sounded. If now we place the opening of a bottle (or bottles) 

 of a resonator, D, over such a heap, the lycopodium is imme- 

 diately blown about in a circle, and may be scattered in any 

 direction by giving suitable inclinations to the resonator. A 

 glass plate held over a heap of lycopodium produces the oppo- 

 site effect by causing it to contract. 



I have succeeded in producing comparatively strong cur- 

 rents of air in still another manner ; but I have not yet found 

 an explanation of these complicated phenomena. 



A cone made of stiff paper was held with its large end oppo- 

 site the opening of a large Kundt's tube. The size of this 

 cone may vary ; but its effect is greatest when it vibrates to 

 the same note as the Kundt's tube, and so forms a resonator 

 open at both ends ; the diameters of its open ends are 37 and 

 7 millims., and its length 90 millims. 



When the Kundt's tube begins to sound loudly, a current 

 of air issues from the narrow end of the cone with such vio- 

 lence that it easily blows out the flame of a candle at a distance 

 of 20 centims. This current rushes through the cone with a 

 peculiar noise, and is easily felt with the finger. 



