M. Dvorak on Acoustic Repulsion. 227 



box has but little vibration, even if the tone of the fork is pow- 

 erful. I have, for example, two boxes with excellent tuning- 

 forks by Konig (of 256 vibrations per second), in which the 

 air would in no wise vibrate powerfully. The strength of the 

 vibration of the air was considerably affected by the degree of 

 tightness with which the fork was screwed to the top of the 

 box. The fork is always vibrated powerfully with a bow ; and 

 two bits of rubber tubing must be on the bottom of the box. 

 I generally use the fork A 3 , of 435 vibrations per second, by 

 Konig. Repulsion is then plainly visible with glass resonator 

 at a distance of 10 centimetres from the opening of the box. 

 With a large fork of Konig (of 128 vibrations) which sounds 

 for more than ten minutes, it was apparent at a distance of 

 20 centimetres. 



The resonators may be tested either by the reinforcement of 

 the sound produced with a tuning-fork, or by the weakening 

 of the sound on approaching them to the opening of the box*. 

 It is not possible to obtain the repulsion of resonators from the 

 prongs of a tuning-fork alone, as their aerial vibrations are 

 too weak (compare Pogg. clvii. p. 42). I formerly tried in 

 vain to obtain acoustic repulsion from vibrating bodies with- 

 out the aid of resonance. I suspended small resonators before 

 the end of a glass tube vibrating longitudinally, and provided 

 with a cork to increase the vibrating surface. The open end 

 of the resonator was probably too near the end of the fork, 

 and so produced a lowering of the tone and acoustic attraction 

 instead of repulsion. Attraction is probably present in all 

 cases, and can assert itself only when not counteracted by 

 greater repulsionj. Later I obtained repulsion very easily in 

 a longitudinally vibrating glass tube 127 centims. long and 

 27 millims. in diameter, on the end of which was a cork 46 

 millims. in diameter. One of the resonators used was sphe- 

 rical (fig. 1, D), and another cylindrical (C). 



I also obtained powerful repulsion with a circular disk 31 

 centims. in diameter and 2 millims. thick, made by Konig. 

 The plate was fastened in the centre in a vertical position and 

 made to vibrate in six segments, producing a note of 208 vi- 

 brations. The resonator was made of stiff paper of the form 

 of B (fig. 1) ; ah equal 80 millims., cd 140 millims., /# equal 



* This is perhaps connected with a conversion of the aerial vibrations 

 in the box into the work of repulsion. The vis viva of the sound-vibra- 

 tions disappears to reappear as work. 



t These experiments were also described in a previous communication. 

 In the apparatus represented (fig. 2), repulsion is easily converted into 

 attraction by diminishing the opening of the resonator with wax, and so 

 throwing it out of tune. 



Q2 



