22 TRUE SURFACES AND ACCURATE MEASUREMENTS—ROBB,. 
pressure of the upper plate is not sufficient to overcome the 
capillary attraction, and force the oil out. It will at once be 
recognized that this is the principle upon which all lubricated 
bearings or journals of machinery, whether flat or round, are 
constructed. This somewhat minute and elementary explanation 
is given in order to show the importance of truth in the surfaces 
of the bearings of machinery, to have flat bearings truly flat 
and round bearings truly round. If such surfaces are uneven, 
as they will be when made by the ordinary method of turning 
or planing, owing to the springing of the cutting tools and 
uneven texture of the metal, lumps will be produced which will 
project through the oil, and the metals will touch each other 
producing, when moving past each other at a high rate of speed, 
friction and wear so common in machinery. But it has been 
proved by experiment that, if the surfaces be made nearly true, 
so that the lubricant will completely separate the metals, and 
the bearing sufficient in area to withstand the weight imposed 
without forcing the oil out, such journals may be run without 
wear, and that the rate of speed, within practicable limits, makes 
no difference. The question ‘will at once suggest itself: Why 
not make all the bearings of machinery perfectly true, suffi- 
ciently large in surface, provide continuous lubrication, and 
prevent wear entirely? J may say that a very great advance 
has been made in this direction. In the higher grades of 
machinery, manufacturers use delicate grinding and scraping 
processes to produce smooth and true surfaces, with the result 
that many machines, such as electric dvnamos and steam engines, 
which run at a high rate of speed, have practically no wear in 
their journals, but it is just here the mechanic learns how hard 
it is to obtain absolute perfection. He may be able to produce 
a sufficiently true surface, but he finds he cannot overcome the 
distortion of metals, due to unequal pressure, or heat. As he 
approaches greater refinement in producing true surfaces, he 
will learn that it is impossible to get them to remain true when 
subjected to the strains incident to the conditions under which 
they work. He finds that, if he lifts his surface plate by one 
corner it is less true, if I may be allowed the expression, than 
