. The London, Edinburgh and Dublin philosophical magazine and journal of science. ouched by the out-side air, as can easily be shown by means of a sensitive mano-meter. To obtain resonance the opening of the cylinder is turnedtoward the source of the sound ; and the cylinder is then re-pelled by the excess of pressure within. Resonators not havinga cylindrical form, but open at one end, are also subject to suchrepulsion. In my previous communication I have indicated * From the American Journal of Science and Arts for July from the Annalen der Physik und Chemie, Band iii. No. 3;
. The London, Edinburgh and Dublin philosophical magazine and journal of science. ouched by the out-side air, as can easily be shown by means of a sensitive mano-meter. To obtain resonance the opening of the cylinder is turnedtoward the source of the sound ; and the cylinder is then re-pelled by the excess of pressure within. Resonators not havinga cylindrical form, but open at one end, are also subject to suchrepulsion. In my previous communication I have indicated * From the American Journal of Science and Arts for July from the Annalen der Physik und Chemie, Band iii. No. 3;dated Agram, November 19, 1877. Phil, Mag. S. 5. Vol. 6. No. 36. Sept. 1878. Q 226 M. Dvorak on Acoustic Repulsion. means for observing the acoustic repulsion of resonators. Asthe method described there is not very sensitive, I have replacedit by the following. The resonators here employed are usuallymade of stiff drawing-paper covered with gum-arabic, andhave the shape of a cylinder, with a little paper tube, hf, atone end (fig. 1, A). This little tube may also be omitted (as. in B) : in that case the resonator is tuned by increasing ordiminishing the little opening, fg. Even a cylindrical tubeopen at one end, C; may serve our purpose as a resonators of glass, D, which a practiced glass-blower can make as light as paper resonators, are note of the resonators is determined by gently blowingover the opening or by tapping. The resonator is fastened with sealing-wrax to the end of alight wooden rod, the other extremity of which is providedwith a counterpoise of lead, 0 (fig. 2). The centre of the rodhas a glass cap, H, w<hich 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 withan ordinary brass Helmholtz resonator weighing, with the leadcounterpoise, 142 grams*. With every tuning-fork we mustfirst ascertain whether the air in the resonating box vibr
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