108 



Mr. G. F. Rodwell on some Effects 



of 52 millims., the distance of the orifice of A from that of C 

 being the same throughout. 



It is thus seen that the lateral action is nearly four times 

 as great in the axis of the jet as at its circumference ; and we 

 should naturally expect the particles in the axis to move with 

 far greater velocity than those at the circumference, for the same 

 reason that the water in the centre of a river moves faster than 

 that near the banks. The same effect must obviously also ob- 

 tain with solid particles such as sand, and even with large masses 

 of matter. Who has not observed the passage of a crowd through 

 a narrow channel (the corridor of a theatre for instance), and 

 the rapid movement of the centre stream compared with that of 

 the side streams ? The individuals composing the centre stream 

 make use of those at the sides as friction rollers ; moreover the 

 latter are impeded by friction against the walls of the corridor. 

 The passage of water or steam through a resisting medium is 

 perfectly analogous ; hence the results mentioned above. 



A tube A, fig. 7, was fitted with a brass cap B, capable of 

 being screwed steam-tight upon the stopcock. A was 450 mil- 

 lims. longand 5 millims. in internal diameter ; the length of the. 

 crosspiece C was 150 millims. Within C a brass tube 325 mil- 

 lims. in diameter was introduced, so that the steam issuing from 

 the stopcock passed through it instead of entering C. The lower 

 end of A dipped into a vessel of mercury D, and a scale was 

 attached to A to show the height to which mercury ascended in 

 virtue of the lateral action of the steam-jet issuing from the brass 

 tube within C. The greatest effect was found to be produced 

 when the orifice of the brass tube was about 45 millims. from 

 the orifice of C. 



The following results were obtained : — 



Pressure of steam, 



in millimetres of 



mercury. 



Height to which 

 the mercury as- 

 cended in A. 



Atmospheric pres- 

 sure (barometer 

 = 760 millims.) 

 reduced to 



millims. 

 1013 

 1165 

 1292 



millims. 

 330 

 380 

 407 



millims. 

 430 

 380 

 353 



It is thus seen that, by an arrangement of this kind, the lateral 

 action of a jet of steam having a pressure = 1165 millims. of 

 mercury* is competent to reduce the atmospheric pressure to 

 one-half. 



* Equal to T6171 kilogramme on a square centimetre, or to 23 lb. on 

 a square inch. 



