144 THE SCIENTIFIC PAPERS OF 



is based on the principle of conservation of momentum in the 

 combined jet of steam and water ; but although the source of 

 power in both cases is a steam jet, the mode of action in the water 

 injector differs essentially from that of the steam jet applied to 

 propulsion of air, as in the former case the steam is' condensed by 

 contact with the water, and ceases to be an elastic fluid at the 

 moment of issue, while in the latter the steam forms with the air 

 a combined elastic stream. 



A very elaborate investigation of the ordinary steam jet applied 

 to propulsion of air was given by Professor Zeuner of Zurich 

 in 1863, showing the effects produced by varying the relative 

 areas of inflow of the air and steam, and varying the steam 

 pressure employed. These theoretical enquiries, which were 

 supported by elaborate experiments, have since been consider- 

 ably advanced by Professor Rankine, who has shown that in 

 the combined stream a considerable portion of the total mo- 

 mentum is lost, and that the relative proportion of this loss 

 increases with the difference of velocity between the component 

 streams. 



The form of steam jet employed in Zeuner's experiments con- 

 sisted of a contracted steam orifice, directed upwards in the line of 

 the axis of a vertical delivery tube, but terminating a little below 

 the base of the tube ; the length of the tube relatively to its 

 diameter was found to be only of minor importance. Exhaustion 

 of air was effected at the lower end of this delivery tube, or com- 

 pression of air at the upper end. The greatest extent of exhaus- 

 tion or compression that was maintained with steam of two 

 atmospheres effective pressure amounted to 7 inches of mercury ; 

 and 100 volumes of steam measured at atmospheric pressure 

 were expended in compressing only 7 volumes of air to the 

 above pressure of about \ atmosphere. "With a reduced orifice 

 for the steam jet, a compression of 3^ inches of mercury was 

 maintained, and 37 volumes of air were compressed by the 

 expenditure of 100 volumes of steam measured at atmospheric 

 pressure. 



In a corresponding experiment made with the improved steam 

 jet shown in Plate 23, maintaining a vacuum of 3 inches of 

 mercury, 137 volumes of air were removed by the expenditure of 

 100 volumes of steam, both measured at atmospheric pressure ; 



