Gases under High Pressure?. 187 



whether any alteration of discharge is caused by a reduction 

 of this lower pressure beyond a certain point. To carry 

 out the investigation on a sufficient scale would need a 

 powerful air-pump capable of absorbing the discharge, but 

 otherwise the necessary apparatus is simple. In order to 

 measure the discharge, or at any rate to determine whether 

 it varies or not, the passage of atmospheric air to the nozzle 

 might be somewhat choked. The accompanying diagram 

 will explain the idea. A is the nozzle, which would be varied 

 in different series of experiments ; B the recipient, partially 

 exhausted, vessel; C the passage to the air-pump. Above 



-IU 



B 



the nozzle is provided a closed chamber E into which the 

 ■external air has access through a metal gauze D, and where 

 consequently the pressure is a little below atmospheric. 

 F represents (diagrammatically) a pressure-gauge, or micro- 

 manometer, whose reading would be constant as long as the 

 discharge remains so. Possibly an aneroid barometer would 

 suffice ; in any case there is no difficulty in securing the 

 necessary delicacy*. Another manometer of longer range, 

 but only ordinary sensitiveness, would register the low 

 pressure in B. In this way there should be no difficulty in 

 attaining satisfactory results. If F remains unaffected, 

 notwithstanding large alterations of pressure in B, there are 

 no complications to confuse the interpretation. 



Terling Place, Witham. 

 June 10, 1916. 



* See for example Phil. Trans, cxcvi. A. p. 205(1901); Scientific 

 Papers, vol. iv. p. 510. 



