produced by a Jet of Water, 237 



circular aperture of 3 - 5 millims. in diameter, the experiment suc- 

 ceeded even when the aperture of the upper plate was 0'5 millim. 

 smaller or greater. Even when a suitably bent strip of lead was 

 placed on one side of the jet at a proper distance from the 

 aperture, notes were formed which changed with the distance of 

 the strip. 



When small apertures were used, the notes produced with the 

 smaller cylindrical apparatus A were more easily obtained, and 

 were richer and more varied as to height and quality ; while 

 those produced with the apparatus B fitted on the cask were 

 feebler, but altered more uniformly with the pressure of water 

 and the distance of the plates. More powerful jets also produced 

 more powerful tones in the larger apparatus. 



The size and shape of the aperture influences the character 

 of the tone produced; so that with another aperture, other 

 circumstances being the same (that is, the pressure of water and 

 the distance of the upper plate), different notes are in general 

 formed ; yet no definite connexion could be ascertained to exist 

 between the dimensions of the apertures and the height and 

 other characters of the note. 



If the two plates are cemented together by a cork ring, the 

 whistle thus formed gives more or less distinct and rich notes, 

 which depend upon the velocity of efflux, and are less change- 

 able than those hitherto described. 



As compared with the sounds produced by air, those obtained 

 with water are in general lower and feebler, and have smaller 

 compass and variety. The pressure under which the jet of water 

 emerges must be greater, but the distance of the plates smaller 

 than in the case of air. The pressure most suitable for the forma- 

 tion of a sound with a jet of water appeared to be between 5 

 and 16 inches, while in the earlier experiments on the production 

 of sounds by air a pressure of from 1 to 30 millims. was gene- 

 rally used. The distance of the plates in the former case was 

 about half that which was found suitable in the latter. 



The author gives as a law, which holds good for the notes of 

 the jet of water within certain limits, that the number of vibra- 

 tions of the notes belonging to the same scale are as the square 

 roots of the pressures, or as the velocities, and are inversely as 

 the distance of the upper plate from the aperture. If the ve- 

 locity of efflux and the distance of the plates be changed, a few 

 notes of definite height become prominent from their rich quality, 

 or pauses result between definite notes. For such a character- 

 istic note or such a pause the ratio of the corresponding velocity 

 of efflux and the distance of the plates is almost constant. 



The author communicates three series of his valuable and 

 multifarious experiments. They indicate an increase in the 



