E a7] 
made two taps, one of 80 and one of rIo threads to’an inch, 
and I made two taps, one of 120 and one of 140 threads to the 
inch; and among thefe taps not above ten or twelve threads 
could be found fufficiently regular for ufe. Thofe, however, 
as workmen know, were enough for original taps, and from 
them by the ufual methods I formed four very good taps of 
the finenefs I have mentioned. In this method I was alfo 
fabje&t to another inconvenience, which was that I frequently 
cut the wire before I had made fufficient impreflion on the 
cylinder. 
I sHouitp not have mentioned this method, as I have very 
much improved upon it, only that its great fimplicity may 
render it practicable by thofe who cannot execute conveniently 
the tool for this purpofe, of which I now proceed to give the 
Aefcription, together with the manner of ufing it. 
(aa) is a fmall vice which is opened or clofed at pleafure 
‘by the long milled fcrew (4), its jaws at (c) are punched or cut 
very rough at the infide. It is faftened on the end of the 
cylinder (¢¢) by the {crew (z), and in a plane perpendicular 
to the axis of the cylinder. At the other end of the cylin- 
der (ee) is fixed a fine knife (d), turning up with a hook (1), 
and having in it a long flit (ss) by which it may be pulhed 
on the fcrew (m), fo that any part of the edge which is beft 
may be applied to cut the {crew. The cylinder (ee) turns 
freely on its axis, and flides in the direction of its axis back- 
wards and forwards (but without fhake) in the focket (7), which 
U 2 is 
