234 PROFESSOR O. REYNOLDS ON THE THEORY OF LUBRICATION, ETC. 
to these experiments do not apply to ordinary cases, does not show that the general 
theory, as given in equations (15), (18), and (19). 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 has established its truth as applicable to all cases for 
which the integrations can be effected. 
The circumstances expressed by 
L a 
/A u? -pi K vrt) 0, A, E, B, 
which are shown by the theory to be the principal circumstances on which lubrication 
depends, although not the same in other cases, will still be the principal circumstances 
and indicate the conditions to be fulfilled in order to secure good lubrication. 
The verification of the equations for viscous fluids under such extreme circum¬ 
stances affords a severe test of the truth and completeness of the assumptions on 
which these eauations were founded. While the result of the whole research is to 
JL 
point to a conclusion (important in 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 
perceivable or not. And that the question as to whether this action can be con¬ 
tinuous or not turns on whether the action tends to preserve the matter between the 
surfaces at the points of pressure as in the apparently unique case of the revolving 
journal, or tends to sweep it to one side as is the result of all backwards and forward 
rubbing with continuous pressure. 
The fact that a little grease will enable almost any surfaces to slide for a time has 
tended doubtless to obscure the action of the revolving journal to maintain the oil 
between the surfaces at the point of pressure. And yet, although only now under¬ 
stood, it is this action that has alone rendered our machines, and even our carriages 
possible. The only other self-acting system of lubrication is that of reciprocating 
joints with alternate pressure on and separation (drawing the oil back or a fresh 
supply) of the surfaces. This plays an important part in certain machines, as in 
the steam engine, and is as fundamental to animal mechanics as the lubricating action 
of the journal is to mechanical contrivances. 
