106 THE SCIENTIFIC PAPERS OF 



scnted by a jet of steam issuing out into the atmosphere was 

 simply the product of the column in feet representing that pressure, 

 multiplied by the weight of steam in Ibs. issuing in a given time. 

 The column representing the pressure of steam of four atmo- 

 spheres total pressure was, according to the table, 45,792 feet ; 

 that was, steam of a pressure of 60 Ibs. would be produced by a 

 column of its own weight 45,792 feet high. Therefore, 45,792 

 foot-lbs. was the mechanical work due to 1 Ib. of that column 

 of steam. Now the quantity of heat contained in 1 Ib. of steam 

 was 1,150 units. These 1,150 units of heat produced in the 

 injector 45,792 foot-lbs. of work, or for every unit of heat 



45 792 



- = 39'8 foot-lbs. The full mechanical equivalent of a unit 

 l,loO 



of heat was however = 772 foot-lbs., or units of force, and therefore 



39 *8 

 the maximum useful effect of the injector did not exceed _^j,or 



/ la 



about the twentieth part of the theoretical effect due to the heat in 

 the steam. A good expansive steam-engine would give as much 

 as one-sixth part of the full theoretical effect due to the heat 

 expended, and supposing that there was 33 per cent, loss in an 

 ordinary pump, it followed that water could be raised with an 



33 



expenditure of 6 + y^; = 8 times the theoretical expenditure of 



heat, instead of 20 times that quantity which the injector required. 

 Consequently, the injector could only be advantageously applied, 

 when the water was required to be both heated and raised ; and 

 it could never compete with an engine and pump for simply rais- 

 ing and propelling water. 



