TRUE SURFACES AND ACCURATE MEASUREMENTS—ROBB. 23 
when resting upon its three supports, or that his straight edge, 
which was about straight when resting upon the surface plate, 
bends slightly when he liftsit by the ends. A machine designed 
and constructed with the greatest care and skill, when subjected 
to the necessary strain of belts, or the inertia of its own rapidly 
moving parts, will spring so that the bearings, which have been 
made nearly perfect in surface and alignment, are thrown slightly 
awry, causing the strain to be borne by a decreased area, and 
forcing the lubricant out. The skill of machine designers is 
shown in designing a machine so that the journal and its seat 
will spring together, thus preserving the adjustment of bearing 
surfaces. We hear and see much in these days of ball bearings. 
The success of the modern bicycle depends upon this ingenious 
device, and has induced almost a mania for using hardened steel 
balls for bearings of all kinds. Those engaged in mechanical 
work often forget that the old and tried oil lubrication is really 
a ball bearing composed of such perfectly formed balls as only 
nature can produce, and with the advantage that they may be 
replaced or renewed as often as desired with very slight trouble. 
Steel balls are undoubtedly better suited to a bicycle than ordi- 
nary bearings lubricated by oil, because it is impossible to get a 
machine light enough for the purpose and have the bearing 
surfaces large and parts sufficiently rigid to keep the surfaces in 
correct alignment; but in heavy machinery where the strain on 
bearings is so much greater, steel balls, with their small surface 
of contact and tendency to crush, are not as suitable as the 
minute spheres of a fluid suchas oil. In this connection may 
be mentioned a point which is also closely connected with the 
second part of this subject, accurate measurements, viz., that it 
is necessary in the construction of bearings of machinery to allow 
sufficient space for the oil between the metals. If a shaft be 
made as perfectly round and smooth as possible, and of the 
exact size of the bushing or box in which it is to work, which 
is also true, there will be no room for the lubricant. The writer 
has seen this fact well illustrated by a bar which was intended 
to carry revolving cutters in a machine for boring cylinders, 
both the bar and the bush were made as carefully as possible 
