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On the Theory of Lubrication. 



[Feb. 11, 



When the surfaces are completely separated by oil it is difficult to 

 see what can cause wear. But there is generally metallic contact at 

 starting, and hence abrasions, which will introduce metallic particles 

 into the oil (blacken it), these particles will be more or less carried 

 round and round with the journal, causing wear and increasing the 

 number of metallic particles and the viscosity of the oil. Thus the 

 rate of wear would depend or. the metallic particles in the oil, the 



values of c, i, and the velocity of the journal, and hence would render 



the greatest velocity of the journal at which the maximum load with 

 a large value of c could be carried, small ; a conclusion which seems 

 to be confirmed by Mr. Tower's experiments with brass No. 2 at 

 twenty revolutions a minute. 



In cases such as engine bearings the wear causes the radius of cur- 

 vature of the brass continually to increase, and hence a and c must 

 continually increase with wear. But, in order to apply the theory to 

 such cases, the change in the direction of the load (or the velocity of 

 approach of the surfaces) would have to be taken into account. 



That the circumstances of Mr. Tower's experiments are not those of 

 ordinary practice, and hence that the particular equations deduced in 

 order to apply the theory definitely to these experiments do not 

 apply to ordinary cases, does not show that the general theory as given 

 in the general equation could not be applied to ordinary cases were 

 the conditions sufficiently known. 



These experiments of Mr. Tower have afforded the means of 

 verifying the theory for a particular case, and hence have so far 

 established its truth as applicable to all cases for which the integra- 

 tions can be effected. 



The circumstances expressed by — 



which are shown by the theory to be, together with the supply of 

 lubricant, the principal circumstances on which lubrication depends,, 

 although not the same in other cases, will still be the principal cir- 

 cumstances, and indicate the conditions to be fulfilled in order to 

 secure good lubrication. 



The verification of the equations for viscous fluids under such 

 extreme circumstances affords a severe test of the truth and com- 

 pleteness of the assumptions on which these equations are founded - r 

 and the result of the whole research is to point to a conclusion 

 (important to natural philosophy) that not only in cases of intentional 

 lubrication, but wherever hard surfaces under pressure slide over each 

 other without abrasion, they are separated by a film of some foreign 

 matter, whether perceptible or not; and that the question as to 



