PHYSICS. 343 



the highest part of the Ehine province. The ground is gently undulat- 

 ing and densely wooded. The valley, spacious on the eastern side, 

 narrows rapidly at one part to a sort of pass, through which, for about 

 a kilometer, the Roderbach flows westward. A southwest wind was 

 blowing, and 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 neighborhood, and 

 some other sounds heard soon afterward satisfied him that the effects 

 were of natural origin. Tones were heard growing in force to a maxi- 

 mum, 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 mixtures of sounds, some of which 

 abruptly stopped. Reuleaux supposes bodies of air in vortical motioji 

 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 

 tronibes, producing oscillations. There was a marked difference of tern' 

 perature 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 press- 

 ing on the warm below and closing the pass to a sort of tube. The 

 wind seemed to be active only in the lower parts. {Froc. Nat. Hist. 8oc. 

 Rlieinl. & Westphal; Nature, October, 1881, xxiv, 592.) 



Kohlrausch has investigated the production of sounds by a limited 

 number of vibrations. A strip of wood 3 meters long had one end 

 fastened to the ceiling, the other carrying a weight of G kilograms, the 

 whole forming a pendulum. A metallic arc, whose center was the point 

 of suspension, was attached below, pierced with equidistant holes, in 

 which teeth are solidly fixed. Beneath this a card is fixed carried by a 

 piece of wood. When raised it is struck by the teeth in i^assing, thus 

 producing a series of impulses varying in time with the distance of the 

 teeth and the velocity of the pendulum, but in number determined by 

 the number of teeth. The velocity of the pendulum was measured by 

 a chronoscoi^e. The pitch of the sound was fixed by a monocord, the 

 bridge being placed at first so that the sound of the cord was evidently 

 more acute, then more grave, than that of the pendulum. The inverse 

 ratio of the two lengths of the cord measures the characteristic interval 

 of height for the sound considered, i. e., the diflerence of height which 

 permits two sounds near to one another to be distinguished. The au- 

 thor's results approximately verify Belmholtz's theory of audition. A 

 sound can be distinguished from another which makes two vibrations, 

 more or less, if the interval of the two sounds is not smaller than ff. 

 Sixteen vibrations were found to be sufficient to determine the pitch of 

 a sound. The method, however, does not claim great delicacy. ( Wied. 

 Ann., 1880, x, 1; J. Fhys., May, 1881, x, 213.) 



Montigny has studied the efle(;t of liquids upon the vibration of bells, 

 the liquids being either within or without them. He finds that (1) the 



