﻿Orifices, and Entrainment of Air by the Issuing Jet. 983 



which, as has been shown, must be considered essentially 

 orifices in thick disks, exhibit points of inflexion at R, Q, 

 and P respectively corresponding to pressures of 3, 5, and 

 12 cm. of water. During the course of the experiments 

 with orifices 9 and 10, anomalous behaviour of the jet 

 in the region of these respective pressures was very readily 

 detected, as the galvanometer reading became very unsteady 

 unless the jet was protected very carefully from outside 

 disturbances. JSteady deflexions could be obtained by 

 reducing outside atmospheric disturbances to a minimum. 



5 10 15 



PRESSURE (CMS. OF WATER ) 



20 



25 



Foi values of the pressure at the orifice, below the critical 

 value, the galvanometer deflexions were exceedingly steady. 

 The galvanometer deflexion was unsteady until the value of 

 the pressure was increased to a definite value, above the 

 critical value, and thereafter the deflexions were again 

 extremely steady. The phenomenon indicates the existence 

 of a small range of pressures over which the issuing jet 

 is essentially unstable, the efficiency of the jet as regnrds 

 air entrainment being very considerably affected by slight 

 disturbances in the surrounding atmosphere. 



The nature of the instability of the jet is most clearly 



