206 Scientific Proceedings, Royal Dublin Society. 



uniform in size, nor do they separate at equal intervals. Hence 

 all drops arriving at the same part of the stream are not in the 

 same phase, and consequently they do not produce the appearance 

 of swellings. The interval between one swelling and the next is 

 the space described by the drop during one complete vibration, 

 and is proportional, as Plateau has shown, to the square root of 

 the head. 



The disturbances by which equilibrium is upset are impressed 

 upon the fluid as it leaves the aperture. What really happens is, 

 according to Prof. Magnus, that the rim of the orifice vibrates up 

 and down, and the issuing stream receives alternate retardations 

 and accelerations which lower down effect its resolution into drops. 



The continuous portion of the jet represents the distance 

 travelled by any one of its elements before disintegration takes 

 place; and its length depends upon the amplitude and wave-length 

 of the disturbance. 



Now, if we have a jet of water which is influenced by a tuning- 

 fork in the manner described, and another tuning-fork of slightly 

 different pitch be sounded, and placed beside the first, producing 

 beats with it, the continuous part of the stream will lengthen and 

 contract in a remarkable manner, keeping time with the audible 



This seems to be due to the fact just mentioned, namely, that 

 the point of disintegration of the jet is determined, ceteris paribus, 

 by the amplitude of the vibration affecting it. When the vibra- 

 tions of the two forks coincide in phase, the resultant vibration has 

 a maximum amplitude equal to the sum of the amplitudes of the two 

 components, and the jet breaks high up. When the phases are 

 opposite, the resultant amplitude is a minimum, and so the clear 

 portion is lengthened. The stream is extraordinarily sensitive to 

 these beats, and will indicate them when the forks have become 

 inaudible. 



If the stream be allowed to flow on to a stretched mem- 

 brane of parchment or thin rubber, placed below the point 

 where drops are formed, the impact of the drops will, in general, 

 be heard as a series of taps — a mere noise. 1 



1 See " Sympathetic Vibration of Jets," by C. A. Bell, m.b., Phil. Trans. Eoyal 

 Society, Part 2, 1886, p. 399. 



