NATURAL PHILOSOPHY. 183 



naked eye can easily reckon the atmospheric vibrations, especially when it is 

 divided in periods by the periodical intervention of a chronometer. It is 

 very curious to examine the variations which the curves undergo when the 

 sounds are the results of the component parts of different harmony; for 

 instance, a note with its octave, third, fourth, or fifth, or any other consonant 

 relation, as the seventeenth or nineteenth. When the sounds are very nearly 

 in harmony, but not in perfect accord, their simultaneous resonance produces 

 beats, and these beats are perfectly indicated or made known to the naked 



eye. 



Concerning this invention, the London Literary Gazette says : ' ' The sci- 

 ence of acoustics has received at the hands of M. Scott a means of develop- 

 ment of which we can form no idea at present. We can only compare his 

 invention to that of M. Daguerrc, which, in its infancy, was treated as a 

 mere toy, but which has now become one of our most valuable scientific 

 instruments of observation. The human voice offers certain difficulties at 

 present; but there is little doubt that eventually the phonautograph will be 

 made capable of superseding every species of stenography, and not only the 

 words, but the very tones of our talented speakers and actors will, by its aid, 

 be registered for future generations. 



ON THE VIBRATIONS OCCASIONED BY WATERFALLS, DAMS, ETC. 



Prof. Snell, in an article in Silliman's Journal, Sept. 18-59, in reviewing the 

 subject of the vibrations occasioned by water falling over dams, etc., says: 



This seems to be one of the numerous cases in which the body which 

 excites vibrations in another, is itself thrown into synchronous vibration by 

 reaction, and then, by its own inertia, or elasticity, controls the common rate 

 of both. The sheet of water in its descent first produces rarefaction of the 

 inclosed air by removing a part of it. The immediate effect is a collapse of 

 the sheet of water, as well as a rush of air in at the ends. But the inertia of 

 a thick mass of water will prevent its recovering its natural position so soon 

 as if it were thinner; hence the air-column divides itself into such a number 

 of segments, that the water and the air can adjust their movements to each 

 other. In a manner somewhat like this, a stream of air from the lips, driven 

 across the embouchure of a flute, excites vibrations in the column of air, 

 with such frequency that it can itself vibrate in unison with it. But, if the 

 stream is blown more and more swiftly, its elasticity will at length be too 

 great for so slow a rate, and then the column will divide into shorter seg- 

 ments, and the two will continue their vibrations harmoniously upon a 

 higher key. A skilful player can in this way, by his mere breath, produce 

 six or eight harmonic notes on the flute, when all the holes are closed. 



In one instance, at Holyoke, Mass., where the oscillations were only eighty- 

 two per minute, I was surprised by the great strength of the current of air, 

 as it rushed into the opening at the end of the dam. I could not venture 

 within the passage through the pier, lest I should be swept in behind the 

 sheet; nor could I stand at the entrance of the arch, without bracing myself, 

 by placing both hands on the corners. There was, however, no alternate 

 outward blast, but only a lull, or cessation of all motion ; which shows that 

 the excess of air that pours in at every pulse, is carried out again in some 

 other way : and there is no conceivable way for it to escape, except to be 

 driven down by the falling water, and poured up externally in a bed of 

 foam. It had never occurred to me before, that the velocity of the air- 



