40 Mr Russell on the Fallacies of the 



der, piston, rod, and cranked axle are superseded, in the most 

 common form, by a cylinder, valves, stop, and axis. In the 

 same way as a mill-wheel is compelled to move in a circle, 

 either by the direct action of water or wind upon it, so is the 

 drum or wheel, with valves, fans, or other projections on its 

 circumference, urged round by the force of the steam, and, en- 

 closed in an outer cylinder or case, gives i-evolution to an axis 

 to which it is attached. This direct rotating action of the 

 steam will, it is imagined, give out its effect more powerfully, 

 uniformly, and economically, than the common mode of reci- 

 procating action, when converted by the crank into revolution. 



Rotatory engines may be arranged according to the mode of 

 action into four classes. 



Class I. — Rotatory engines of Simple Emission. 



Class II, — Rotatory engines of Medial Effect. 



Class III. — Rotatory engines of Hydrostatical Reaction. 



Class IV. — Rotatory engines of the Revolving Piston. As 

 closely connected with the rotatory engines in the fallacy 

 which has given rise to both of them, we may add a series of 

 inventions forming a 



Class V. — Revolving Mechanism substituted for the Crank. 



Class I. — The rotatory engine of Simple Emission forms the 

 earliest, as well as the most rude and elementary method of 

 giving motion to mechanism, by the escape of vapour or steam. 

 It is described by Hero of Alexandria, in his Pneumatika, up- 

 wards of 120 years before Christ, and depends, for its effect, 

 upon the same principle which gives to a rocket its career, and 

 makes a fire- wheel revolve in giving off its beautiful lights. In 

 these, as in all instances where fire, or steam, or any fluid or gas 

 is generated in a chamber from which it is permitted to issue 

 with violence, it will, in its exit, drive the vessel from which it 

 issues away from it in the opposite direction, and is, in fact, 

 merely an applicat on of the principle of recoil, — where the gas, 

 generated by the explosion of the powder, urges the ball out- 

 wards in one direction, and forces the breech of the gun back- 

 wards in the opposite one. The same recoil is felt in all cases 

 of simple emission of a fluid from a reservoir ; and if it be so 



