in the Construction of Steam-En gives. 343 



large and the condenser, iiinst be Gpened : the steam last 

 admitted into the lower part of the smaller eylinder will 

 now ascend into the top of the larger and expand itself, 

 fallowing the piston of the larger cylinder which is now 

 descending, its other side being open to the condenser; 

 and (as the tops of the two cylinders communicate) steam 

 will also pass into the top of the smaller cylinder above its 

 piston, so that both pistons descend together to the bottom 

 of their respective cylinders ; when a fresh charge of steam 

 is again to be admitted for a fresh stroke of the engine. 



4ihly. if m-y improvements be applied to one of the en- 

 gines known by the name of Watt's double engine, the 

 working cylinder must have no direct conmiunieation with 

 fne boiler, but must be made to communicate at its top 

 and bottom alternately with the lower and upper part of 

 the smaller added cylinder, or simply, as the case may be, 

 St its top and bottom, with the steam measure, which has 

 a direct communication with the boiler ; the effect of which 

 must be sufficiently obvious from the details I have alreadv 

 given respecting the nature of my invention, and the way 

 in which the same is to be carried into actual practice. 



5thly. Vv'itli regard to steam-engines, in which the se- 

 parate steam measure may not be tliought advisable, the 

 same may be improved by the application of my aforesaid 

 discovery, by making the boiler, and the steam case cw cases 

 in which the working cylinder or cylinders is or are in- 

 closed, much stronger than usual ; and by altering the struc- 

 ture and dimensions of the cocks, valves, slides, or other 

 means of admitting steam from the boiler into the cylinder 

 or cylinders, in such a manner as that the steam may be 

 admitted very gradually by a progressive enlargement of the 

 aperture, so as at first to wiredraw, and afterwards admit 

 more freely the same. The reason for this precaution is 

 this : Steam of such great elastic force as I employ, if ad- 

 mitted suddenly into the cylinder or cylinders, wh.en more 

 than one working cylinder is employed, would strike with 

 a force that would endanger the safety and durability of the 

 engine. The aperture allowed to the valve, cock, or other 

 contrivance for admitting steam into the cylinder or cylin- 

 ders, should be regulated by the following consideration : — 

 If the intention is that the engine should work only, or al- 

 most wholly, by condensation, the steam in passing into 

 the cylinder or cylinders should be forced to wiredraw itself, 

 as I have already said, but so that the pistou or pistons 

 may perform the whole or a great part of the stroke by the 

 time the intended quantity of steam has been admitted into 

 y 4 the 



