CHAPTER III. 



ON ACOUSTIC PRESSURES AND ACOUSTIC DILATATIONS, CHIEFLY 



IN RESERVOIRS. 



13. Introductory. Apparatus. On a number of occasions heretofore,* I 

 have endeavored to use the interferometer for the measurement of Mayer and 

 Dvorak's f phenomenon, but though the experiments seemed to be well 

 designed and were made with care they invariably resulted in failures. The 

 present method, however, has been successful and has led to a variety of sur- 

 prising results, even if the term acoustic pressure is not directly applicable. 



The apparatus is shown in figure 14, where B is a mercury manometer 

 described in Chapter I, the displacements being read off by the component 

 rays L, L' of the vertical interferometer. The mercury of the U -tube is shown 

 at mnm', above which are the glass plates g, g', the former being hermetically 

 sealed, the latter loose, so that the air has free access. The closed air-chamber 

 R, above m, receives the air-waves from the plate of the telephone T, by means 

 of the quill- tubes t, hermetically sealed into the mouth-piece of the telephone, 

 and t' sealed into the manometer. Finally, t" is a branch tube ending in a small 

 stop-cock C, or similar device at one end, while the other communicates with 

 it'. Flexible-rubber tube connectors may be used at pleasure, so long as the 

 space bounded by the outer face of the telephone plate, the mercury surface m, 



and the stop-cock C are quite free from leaks. The cock C will eventually 

 be replaced by the glass quill-tubes c and c' (enlarged) perforated with minute 

 orifices at 0. 



The telephone is energized by two storage-cells and a small inductor, with a 

 mercury or other break. Large resistances are to be put in the telephone cir- 

 cuit, so that the inductances are of secondary importance. The bore of the 

 tubes t, t', c, c' need not exceed 5 mm. Thus the R chamber in B, about 6 cm. 

 in diameter and 2 cm. deep, is the resonator (capacity with appurtenances, 57 

 cm. 8 ) of the apparatus. 



*Cf. Carnegie Inst. Wash. Pub., No. 149, Part III, 122. 1914. 



t This and the Konig resonators are adequately described in most large text-books 

 (cf. Chwolson, Acoustic g 5, Vieweg edition). Reference should be made to Bjerknes's 

 famous treatise of hydrodynamic forces in pulsating media (Earth, 1902); to the papers of 

 W. Konig, Wied. Ann. xlii, xliii, 1891, and others. 



Recently much work along similar lines has been done by Prof. A. G. Webster and his 

 students. Cf. A. T. Jones, Thesis, Clark Univ., 1913, on the acoustic repulsion of gas-jets; 

 and Phys. Review, xvi, p. 247, 1920, on the tone of bells; H. F. Stimson, Clark Univ., 1914, 

 on interferometer methods in acoustics. 

 14 



