142 THE SCIENTIFIC PAPERS OF 



steam, equal to that of the ordinary fan blast, and even of the 

 steam engine and pump. 



This improved steam jet is shown half full size in the longi- 

 tudinal and transverse sections, Figs. 2 to 5, Plates 23 and 24. 

 A very thin annular jet of steam is employed, in the form of a 

 hollow cylindrical column, discharged from the annular orifice 

 between the two conical nozzles A and B, the steam being supplied 

 from the pipe into the space between the two nozzles. The 

 inner nozzle A can be adjusted up or down by the hand screw D, 

 so as to diminish or increase the area of the annular orifice 

 between the two nozzles, for regulating the quantity of steam 

 issuing. The air to be propelled by the steam jet is admitted 

 from the pipe E through an exterior annular orifice surrounding 

 the steam jet, and also through the centre of the hollow jet. The 

 tube G, into which the steam jet issues, is made of conical shape 

 at the bottom, so as to form with the outer nozzle B a rapidly 

 converging annular passage for the entrance of the air ; and the 

 width of this air passage is regulated by adjusting the nozzle B 

 by means of the nut H at bottom. The tube Gr continues to 

 converge very gradually for some distance above the jet orifice, 

 the length of the convergent portion increasing with the width of 

 the outer annular air orifice, and also with the steam pressure 

 employed ; the most advantageous length varies from 12 to 20 

 times the width of the annular air orifice, the object being to 

 ensure the complete commingling of the steam and air within the 

 length of the mixing chamber G-, beyond which the tube gradually 

 increases in diameter in a parabolic curve to the upper end, as 

 shown in Fig. 1. A tapering spindle I is sometimes fixed in the 

 centre of the inner nozzle A, and carried up through the mixing 

 chamber G, for the purpose of preventing reflux through the 

 centre of the combined current. 



The rationale of this arrangement is as follows. First, by 

 gradually contracting the area of the air passages on approaching 

 the jet, the velocity of motion of the entering air is so much 

 accelerated before it is brought into contact with the steam, that 

 the difference in the velocity of the two currents at the point 

 where they come together is much reduced, and in consequence 

 the eddies which previously impaired the efficiency of the steam 

 jet are to a great extent obviated, and a higher useful result is 



