56 Mr Russell on the Fallacies of the 



It is a received principle in constructing machines, that, in a 

 good engine, the parts should wear equally, and that even the 

 very working of their parts should make them fit each other bet- 

 ter. This is truly the case with the piston and cylinder and 

 other appendages of the reciprocating steam-engine. So true, 

 that old engines of Messrs Watt and Bolton — some of their ear- 

 liest — are still working better than they ever did, or than some 

 more recently made. To this the reciprocating engine necessarily 

 presents a contrast ; and it will not be difficult to shew that its 

 parts must wear unequally, so as to become unfit for use, and 

 be rendered by each day's work less fit for the duty of the suc- 

 ceeding one. 



To shew the cause of this : — Suppose two perfectly flat plates 

 of metal, perfectly round, to be laid one upon the other, so as 

 exactly to coincide at every point. Let the undermost rest 

 upon a table, and let the uppermost be so made as to turn 

 round on an axis while in contact with the other, and let a ra- 

 pid motion be communicated to the uppermost, — let me ask 

 what will be the result of the attrition of the one of these up- 

 on the other ? Will they wear equally, so as to remain in a 

 state of mutual adaptation, or will they not ? Experience fur- 

 nishes an answer which exactly quadrates with reasonable ex- 

 pectation ; — they will not wear equally, — they will not retain 

 their forms. Let it be considered that the outer edge performs 

 a larger circuit than any part nearer the centre ; that, therefore, 

 as all the parts revolve in the same time, those nearer the cir- 

 cumference move with a greater velocity than those towards 

 the centre ; that the attrition is most rapid at the circumference, 

 and uniformly diminishes towards the centre of the plates ; then 

 it inevitably foUows that the plates must become conical, with 

 a continual tendency to become more so. This is a most in- 

 contestible truth. It is one which has caused the failure of 

 many beautiful inventions ; it is the reason why conical bear- 

 ings have been uriversally abandoned for cylindrical ones ; and 

 it is the cause that has rendered a most beautiful class of inven- 

 tions totally useless to the improvement of the reciprocating en- 

 gine. I allude to the flat revolving valves introduced by Oliver 

 Evans, and afterwards brought into this country, but now uni- 

 versally abandoned, in spite of simplicity, efficiency, and econo- 



