Physical Notes

Abstract

A SINGULAR case of the production of sound by natural causes is recorded by M. Reuleaux (Proc. of the Nat. Hist. Soc. of Prussian Rhineland and Westphalia). He observed it while hunting in the Röderbacherthal, near the highest point of the Rhine province. The ground is, in the main, gently undulating and densely wooded. The valley, spacious on the eastern side, narrows rapidly at one part to a sort of pass, through which, for about one kilometre, the Roderbich flows westwards. A sout-west wind was blowing, and M. Reuleaux, coming along the hillside from the east, heard what appeared to be the strokes of a fine deep-toned bell in rapid succession. There was no such bell in the neighbourhood, and some other sounds soon heard satisfied him that the effecs were of natural origin. Tones were heard growing in force to a maximum, then dying away; they were like those of organ-pipes at first, but their “clang” came to resemble that of a harp or violin. At the mouth of the pass, whence the sounds seemed to radiate, there was a strange agitation in the air, and mixture of sounds, some of which abruptly stopped. M. Reuleaux supposes bodies of air in vortical motion (trombes) to have been carried along from the pass, and the sound to have been due to conflict between the outer and the inner air at the mouth of such trombes, producing oscillations. There was a marked difference of temperature between the higher and the lower parts of the valley, and this is regarded as an important factor in the case; the cold air above pressing on the warm below, and closing the pass to a sort of tube. The wind seemed to be active only in the lower parts.