This will perhaps be better understood by
referring to Fig. 66, which is a view of Fig. 65 seen in the direction
of the arrow _c_. Here we see the roller jewel at _D_, and if we bring
it forward as far as the hole in the roller will permit, it will occupy
the position indicated at the dotted lines; and if we set it in (toward
the staff) as far as the hole will allow, it will occupy the position
indicated by the full outline.
[Illustration: Fig. 66]
Now such other condition might very easily exist, that bringing the
jewel pin forward to the position indicated by the dotted lines at _D_,
Fig. 66, would remedy the defect described and illustrated at Fig. 64
without any other change being necessary. We do not assert, understand,
that a hole too large for the jewel pin is either necessary or
desirable--what we wish to convey to the reader is the necessary
knowledge so that he can profit by such a state if necessary. A hole
which just fits the jewel pin so the merest film of cement will hold it
in place is the way it should be; but we think it will be some time
before such rollers are made, inasmuch as economy appears to be a chief
consideration.
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