Polytechnic Association. 857 



The higher the temperature of the steam when it enters the steam 

 cylinder, and the lower that at which it arrives before the exhaust 

 occurs, the greater, science tells us, will be our success, provided we 

 at the same time avoid waste of heat and. power. 



Now, looking back over the history of the steam-engine, let us 

 rapidly note the prominent improvements and the most striking changes 

 of form, and thus endeavor to obtain some idea of the general direc- 

 tion in which we are to look for further advance. 



Beginning with the machine of Porta, at which point we may first 

 take up an unbroken thread, it will be remembered that we there found 

 a single vessel performing the functions of all the parts of a modern 

 pumping engine; it was, at once, boiler, steam-cylinder and conden- 

 ser, as well as both a lifting and a forcing pump. 



The Marquis of Worcester divided the engine into two parts using, 

 a separate boiler. 



Savery duplicated that part of the engine of Worcester which per- 

 formed the several parts of pump, steam-cylinder and condenser, and 

 added the use of water tc effect rapid condensation. 



Newcomen and Cowley next separated the pump from the steam- 

 engine proper, and in their engine, as in Savery's, we noticed the use 

 of surface condensation first, and subsequently that of the jet, thrown 

 into the midst of the steam to be condensed. 



Watt finally effected the crowning improvements, and completed 

 the movement of " differentiation " by separating the condenser from 

 the steam-cylinder. Here this movement ceased, the several impor- 

 tant processes of the steam-engine now being conducted, each in a 

 separate vessel. The boiler furnished the steam, the cylinder derived 

 from it mechanical po^ver, and it was finally condensed in a separate 

 vessel, while the power which has been obtained from it in the steam- 

 cylinder was. transmitted, through still other parts, to the pumps, or 

 wherever work was to be done. 



Watt, also, took the initiative in another direction. He continually 

 increased the efficiency of the machine by improving the proportions 

 of its parts and the character of its workmanship, thus making it 

 possible to render available many of those improvements in detail, 

 upon which effectiveness is so greatly dependent, and which are only 

 useful when made by a skillful workman. 



Watt and his cotemporaries also commenced that movement toward 

 higher pressure of steam and greater expansion, which has been the 

 most striking feature noticed in the progress of steam-engineering 

 since his time. 



