gg0 HYDRAULICS. 



In order to communicate a rotatory motion to 

 any machinery by the motion of the beam of the 

 steam-engine, Mr. "Watt made use of a very large 

 fly-wheel, G; on the axis of which is a small con- 

 centric-toothed wheel, H. A similar toothed- 

 wheel, I, is fastened by straps to a rod coming 

 from the end of the beam, so that it cannot turn 

 round on its axis, but must rise and fall with the 

 motion of the great beam. 



A bar of iron connects the centres of these two 

 small-toothed wheels, so that they cannot quit each 

 other. When, therefore, the beam raises the 

 wheel I, it must move round the circumference of 

 the wheel H, and turn it together with the fly : 

 and it will be evident, upon consideration, that the 

 fly, driven in this manner, will make two revo- 

 lutions for every one of the wheel I. This mode 

 of moving the fly is preferable to a crank, as it 

 goes with twice the velocity : it is called the 

 sun and planet-xchecl, from the resemblance of the 

 motion to that of those luminaries. 



The valves of this steam-engine are all puppet- 

 valves, as these are found least liable to be out of 

 order. 



The mode of operation in Mr. Watt's engine is 

 as follows : 



Suppose the piston at the top of the cylinder, in 

 the situation represented in the plate, and the 

 lower part of the cylinder filled with steam. By 

 means of the handle E, open the steam-valve a, 

 and the eduction-valve d, the levers of which are 

 connected together; there being now a communi- 

 cation between the cylinder and the condenser, 

 the steam instantly rushes into the condenser, 

 leaving the cylinder empty, whilst at the same 

 time the steam from the boiler, entering by the 



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