On Friction. ' 293^ 



in equal times ; because the lighter body will always be found to 

 perform its task in the shorter time, if the resistance increase as 

 any single power of the depth. This, if necessary, shall be de- 

 monstrated afterward. The statement referred to, therefore, 

 does not imply any possible law of resistance. H. M, 



XLVIII. Illustrations and Corrections of two Papers on the 

 Nature and Laws of Friction, with a Refutation of the 

 Objections of Mr. Meikle. Btj Mr. Thomas Tredgold* 



To Mr. Tilloch. 



Sir, — XN your last Number Mr, Meikle has made some ob- 

 jections to a theory of Friction, which you did me the favour to 

 publish in your Numbers for January and July. I hope in this 

 letter to show that those objections are groundless ; but though 

 Mr. Meikle states that he has examined the steps of my inquiry, 

 the real errors he has failed in detecting; and T am sorry to say 

 that in two cases I have overlooked circumstances that ought to 

 have been considered : therefore I take this opportunity of cor- 

 recting them. 



In your Number for January, page 5, it is stated that the 

 indentation is as the extensibility; but it ought to have beert 

 directly as the extensibility, and inversely as the cohesive force : 



P X E 

 That is, the general Prop. (2) ought to have been I 



Cx Lx B 



And then. Prop. (4) becomes F : P x E ; that is, the friction is 

 directly as the pressure and exteneibility and independent of the 

 cohesive force. Tliis correction is important, in as far as relates 

 to the friction of different bodies, but does not affect the results 

 when the materials continue the same. I am sorry that the ef- 

 fect of the cohesive force in resisting indentation was overlooked: 

 the only reparation I can now make is to candidly avow it. 



I must now proceed to examine Mr. Meikle's objections. In 

 the first place, he states that my law of friction in uniform mo- 

 tions is in opposition to several experiments. Now it certainly 

 must have been in your correspondent's power, and therefore it 

 was a duty he had imposed upon himself, to refer to the experi- 

 ments he alludes to ; and to show that they were of an unob- 

 jectionable nature. As he has not done so, 1 can only say that 

 such experiments are unknown to me. 



It has been supposed that the friction is the sam« in uniform 

 motions as it is in accelerated ones; but, independent of mathe- 

 matical reasoning, the incorrectness of this supposition must bo 

 apparent when the distinct laws of these motions are considered. 

 In the description of experiments, and in the usual statements of 



T 3 the 



