﻿Orifices, and Entrainment of Air by the Issuing Jet. 971 



platinum wires. The end of this tube away from the jet 

 opened into a large vessel containing water, which served to 

 saturate the air with water vapour, a condition corresponding 

 to that of the air employed in calibrating the instrument, and 

 to shield the anemometer from outside disturbances. Slightly 

 different calibration curves were employed corresponding to 

 different atmospheric temperatures. The velocity with which 

 the air was set into motion in the tube E by the jet depended 

 upon the length of tube employed. This was chosen of the 

 minimum length consistent with securing steady readings of 

 the anemometer, and was equal to 54 inches. 



The jacketted tube A was inserted into the tube D to such 

 a depth that the velocity of air-stream passing over the 

 anemometer wires was a maximum for the pressure employed. 

 A gas-tight joint was then made between the tubes A and D 

 bv means of the gland Gr screwing down on a rubber ring. 

 If for any cause it became necessary to remove the tube A, 

 it could be readjusted to its former position by reading the 

 position of the pointer P with reference to a scale marked on 

 the tube. The pointer S moving over a circular scale served 

 to indicate the azimuthal position of the orifice disk, and was 

 more especially used in connexion with subsequent experi- 

 ments with multiple-orifice disks. 



(c) Measurement of the Discharge. — The method employed 

 for determining the rate of efflux of air was to determine the 

 time taken for a definite measured volume of air to flow 

 through the orifice. The device employed for this purpose 

 is shown in fig. 2, and is a slight modification of the apparatus 

 employed by Coste *. The measured volume of air is 

 contained between two marks shown on the vessel A. Water 

 is delivered to the vessel through the jet B from a Marriotte 

 bottle or overflow constant-head device, the rate of flow of 

 water being controlled by means of the cock C. The cock 

 D is fully open during the flow of water through B, and 

 closed while the vessel A is subsequently emptied through 

 the cock E, the cock C being meanwhile unaltered. In this 

 manner the rate of flow of water through B is very conveni- 

 ently adjusted to the series of increasing rates of flow 

 employed in the present sequence of experiments. 



Vessels A of various sizes were emplo}'ed in the course of 

 the present experiments, . the smallest having a. volume 

 between marks of 838*2 c.c. and the largest a volume of 

 7081 c.c. The lower stem of the vessel A extended for a 

 considerable distance below the lower mark, so that the 



* J. Soc. Chem. Tnd. vol. xxx. p. 258 (1911), 

 3R2 



