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N. B. The didance betwen two contiguous threads 
is to be meafured by a line parallel to the axle ; if 
we now fuppofe that a hand-fpike or handle is in- 
ferted into the bottom of the convex fcrew, and 
that the power which turns the fcrew is applyed to 
the extremity of this handle, which is generally the 
cafe ; then as the power is removed farther from 
the axis of motion, its force will be fo much en- 
creafed (vide what was faid of the lever, cor i.) 
and therefore fo much may the power itfelf be 
diminifhed. So that the power, which, adting on 
the end of a handle, fudains a weight by means of 
a fcrew, will be to that weight, as the didance be- 
tween two contiguous threads of the fcrew, to the 
periphery deferibed by the end of the handle. In 
this cafe we may confider the machine as compofed 
of a fcrew and a lever, or, as Sir Ifaac Newton ex- 
preffeth it, Cuneus a ve£le impulfus. 
I have now given you my fentiments, as to the prin- 
ciples on which, I think, the efficacy of the mechanic 
powers may be mod; properly explained ; and hope 
that, where 1 have preiUmed to differ from others, you 
will think I have fome appearance of reafon on my 
fide. I find my paper has been drawn out much be- 
yond what I atfirft expe&ed, and I fear much beyond 
your patience j and therefore ffiall detain you no longer 
than to affure you that I am, Sir, 
with the fincereff regard, your 
mod obedient humble fervant, 
Hugh Hamilton. 
XXVI. An 
