176 Prof. Magnus's Hydraulic Researches, 



exactly at the same part of the continuous portion of the stream. 

 Hence they do not all appear vertically elongated at the same 

 part, nor all of their maximum breadth at another single point 

 in the stream ; but at one and the same part are found masses 

 quickly following one another, some vertically elongated, others 

 extended laterally ; consequently they do not produce the im- 

 pression of regular swellings. But that the separated masses 

 are always broadened, appears not only from observation with 

 the rotating disc, but from the fact that the turbid part of the 

 jet is always broader than the smooth continuous portion. 



163. The regular separation of the masses of water is con- 

 ditioned by the vibration of the bottom plate, or, more exactly, 

 by that of the rim of the efflux-hole (as appears from the experi- 

 ment § 134). As this edge moves uniformly up and down, the 

 velocity of the stream which flows out is alternately accelerated 

 and retarded; and through these regularly alternating accelera- 

 tions and retardings the alternating contractions and expansions 

 are produced which, lower down the stream, effect its separa- 

 tion into distinct drops. If these alternate accelerations and 

 retardings are not present, the swellings are wanting, and the 

 separation occurs at a greater distance from the efflux-orifice 

 and svith much less regularity. Probably, when swellings 

 are present, the smaller distance at which the distinct masses 

 separate conti-ibutes, to no small extent, to the increase of regu- 

 larity ; for all motions in the sti'eam are more regular at a small 

 distance from the efflux-orifice than when more remote from it. 



164. The stronger the vibrations of the efflux-orifice, or what 

 comes to the same thing, the greater the intensity of the note 

 which causes these vibrations, the greater also is the difference 

 between the alternating accelerations and retardings, and the less 

 therefore the distance from the efflux-opening at which the sepa- 

 ration takes place and at which swellings are produced. This has 

 been shown by the observations given in § 137. 



The jet flowing out of a very narrow opening. 



165. The following observation furnishes an interesting con- 

 tribution to the effects of the vibrations of the efflux-orifice. 



If water be allowed to flow from a narrow orifice whose dia- 

 meter is less than a millimetre, the small drops into which the 

 stream separates move quite irregularly, somewhat as represented 

 in fig. 13. But on sounding a note, the particles arrange them- 

 selves with great regularity : a certain number always follow one 

 another immediately ; a somewhat greater interval intervenes ; 

 then the former number of drops occur again, as is shown in 

 PI. I. fig. 14. The greater intervals correspond to the elevations 

 of the orifice. 



