12 THE SCIENTIFIC PAPERS OF 



of the succeeding charge of steam before it had forced the piston 

 upwards. 



James Watt, in seeking a remedy against this loss of heat, 

 conceived the possibility of condensing the steam in a separate 

 closed vessel ; and in carrying his idea into effect, he not only 

 realised his immediate object, but at the same time rendered the 

 steam engine susceptible of that degree of perfection and general 

 application which it now possesses. The injection condenser of 

 Watt is the most effectual of its kind, and has maintained its 

 exclusive dominion to the present day. It consists of a closed 

 vessel, which communicates periodically with the steam cylinder. 

 The injection water, together with the condensed steam and the 

 air, which last is partly evolved from the injection water and 

 partly leaks in through the joints of the cylinder and exhaust pipe, 

 are continually discharged from it by means of the air pump. 



Shortly after the introduction of Watt's condenser, a surface 

 condenser was proposed by Hornblower, which consisted of a close 

 annular vessel of thin metal plate, on the inner surfaces of which 

 the waste steam of the engine was condensed ; its latent heat being 

 continually carried off by a stream of cold water which surrounded 

 the vessel. A comparatively small air pump was provided, which 

 served to discharge the condensed water (to be again forced into 

 the boiler) and any air that might leak in through the joints. 

 This condenser failed in practice, for want of sufficient extent of 

 cooling surface. 



An effective surface condenser would possess considerable advan- 

 tages over the injection condenser, especially in the case of 

 marine engines. Allowing the condensed steam to be continually 

 returned into the boiler, it prevents incrustation of the boiler, and 

 moreover dispenses with the necessity of blowing off. Its air pump 

 absorbs a much smaller proportion of the power of the engine, and 

 its functions require less personal attention. Stimulated by these 

 considerations, several attempts were made to improve on Horn- 

 blower's invention ; but since all these improvements partake 

 very much of the same character, it is thought sufficient for the 

 present purpose to mention only Hall's condenser, which has 

 obtained the greatest amount of notoriety. It consists of two flat 

 chests or closed chambers, connected together by means of a large 

 number of brass tubes, through which the condensing steam 



