d a twisting strain has to be resisted
by the slides, whereas in an upright drill the sliding sleeve is
directly over and in line with the drill, and subject to no side
strain.

Does not the foregoing statement that "the propelling power should be
as near the resistance as possible, and the guide be as near in line
with the two as possible," embody the true principle? Neither of the
two methods in common use meets this requirement to its fullest
extent. The two-V New England plan seems like sending two men to do
what one can do much better alone; and the inconsistency of guiding by
the back edge of a flat bed is prominently shown by considering what
the result would be if carried to an extreme. If a slide such as is
used on a twenty inch lathe were placed upon a bed or shears twenty
feet wide, it would work badly, and that which is bad when carried to
an extreme cannot well be less than half bad when carried half way.

The ease with which a cast iron bar can be sprung is many times
overlooked. There is another peculiarity about cast iron, and likely
other metals, which an exaggerated example renders more apparent than
can be done by direct statement. Cast iron, when subject to a bending
strain, acts like a stiff spring, but when subject to compression it
dents like a plastic substance. What I mean is this: If some plastic
substance, say a thick coating of mud in the street, be leveled off
true, and a board be laid upon it, it will fit, but if two heavy
weights be placed on the ends, the center will be thrown up in the air
far away from the mud; so, too, will the same thing occur if a
perfectly straight bar of cast iron be placed on a perfectly straight
planer bed--the two will fit; but when the ends of the bar are bolted
down, the center of the bar will be up to a surprising degree. And so
with sliding surfaces when working on oil. If to any extent elastic,
they will, when unequally loaded, settle through the oil where the
load exists and spring away where it is not.

The tool post or tool holder that permits of a tool being raised or
lowered and turned around after the tool is set, without any sacrifice
of absolute stability, will be better than one in which either one of
these features is sacrificed. Handiness becomes the more desirable as
the machines are smaller, but handiness is not to be despised even in
a large machine, except where solidity is sacrificed to obtain it.

The weak point in nearly all (and so ne