M. Dvorék—Acoustic Repulsion. 23 
The resonator is fastened with sealing wax to the end of a 
light wooden rod, the other extremity of which is provided 
with a counterpoise of lead O, fig. 2. The center of the rod 
has a glass cap, H, which rests on a needle point. 
The best source of sound is a resonant box of a tuning fork, 
fig. 2. The repulsion is so great that it is apparent even with 
an ordinary brass Helmholtz resonator, weighing, with the lead 
counterpoise, 142 grams.* Withevery tuning fork we must first 
ascertain whether the air in the resonating box vibrates with suf- 
ficient energy, because this is not always the case even with accu- 
rately tuned boxes. As the elasticity of the different boards 
which form the elastic system of the box is not equal, their 
vibrations may hinder the formation of the node at the bottom 
of the box ; in this case the air on the bottom of the box will 
vibrate but feebly. We can easily ascertain this fact by accu- 
rately tuning the box to the note of the fork and then observing 
whether the note is considerably weakened by partially cover- 
ing the opening. If it is not, then the air in the box has but 
little vibration even if the tone of the fork is powerful. I have, 
for example, two boxes with excellent tuning forks by Konig 
: Ge 
a glass tube vibrating longitu 
rf 
a lowering of the tone and acoustic attraction instead of repul- , 
_ * The apparatus represented in fig. 3 may be ere 
tion by turning the closed end of the resonator toward the box. 
+ This is perhaps connected with a conversion of t brat 
box into the work of repulsion. The vis viva of the sound-vibrations dis 
E18 sey sie shes fo cho sie ee 
