Several new slide rules for special calculations are described in this
edition, and the contents further extended to include a section dealing
with screw-cutting gear calculations by the slide rule—an application of
the instrument to which attention has been given recently.
Mention should be made of the fact that some of the special slide rules
described in previous editions are no longer obtainable. As, however,
the descriptive notes may be of service to those possessing the
instruments, and are, in some measure, of general interest, they have
been allowed to remain in the present issue.
The author tenders his thanks to the many who have evinced their
appreciation of his efforts to popularise the subject; also for the many
kind hints and suggestions which he has received from time to time, and
with a continuance of which he trusts to be favoured in the future.