Rotatory Steam-Engine. 39 



tain remarkable properties of adaptation to the nature of mat- 

 ter, of motion, of steam, and the human mind ; from which its 

 supremacy as an elementary machine is derived, — properties 

 which cannot possibly belong to any species of rotatory engine. 

 The common or reciprocating steam-engine is distinguished 

 from the rotatory steam-engine by the nature of certain parts 

 of its mechanism, which convey the motion of the steam to the 

 machinery which is to be moved. There are a cylinder, a pis- 

 ton-rod, and a crank-axle. Now the root of the whole of the 

 fallacies of the rotatory engine will be found in certain radical 

 misconceptions of the nature of the crank, as the simple ele- 

 mentary instrument by which the revolving motion of the axis* 

 or great wheel of the steam-engine, is immediately produced. 

 Nothing can be simpler than the crank. We wish to turn an 

 axle round ; we bend a part of the end of it at right angles to 

 itself; we take hold of this end, and by this means turn round 

 the axle. The bent part is the crank, and may be seen every 

 day in winding up a clock, or in turning any wheel on its axle, 

 by holding a spoke ; likewise in the handle of a cofFee-mill, at 

 the top of a draw-well, or in the handle of any winch or crane 

 for raising weights. Now, in the same manner as the hand of 

 the operator takes hold of the handle, and, by drawing it to- 

 wards him or pushing it from him, makes the axle or wheel 

 turn round, — so does a rod from the piston of a steam-engine 

 take hold of the end of a crank, and alternately draw and push 

 it round in its circle of revolution. The crank is indeed so 

 simple that it can scarcely be called an addition to the axle of 

 which it forms a part ; it is merely a bend or cj-ook in it, which 

 the word crank originally implies, and has been used to move 

 the pistons of the cylinders of common pumps, since the days 

 of Aleotti, in precisely the same way as it now moves in the 

 steam-engine. Now, it is owing to a radical misconception of 

 the nature of this elementary machine, that hosts of schemes 

 have arisen for the production of circular motion, without the 

 intervention of the crank, either by giving to the steam itself 

 an immediate circular action, or by the substitution of some 

 other less elementary mechanism, between the reciprocating 

 piston and the revolving axis, as the means of producing its ro- 

 tation. In the rotatory engine, on the other hand, the cylin- 



