C 58 1 
V. EJfay on a new Method of applying the Screw. By Mr*. 
William Hunter, Surgeon ; communicated by Lieutenant Gc~ 
neral Melville, F. R. S. 
Read December 2 1 , 1780. 
I HAVE fome time ago been led to think, that the fcrew*. 
which of all the mechanical powers is the mod commonly 
employed in performing motions which require great accuracy, 
might be applied in a manner which would better anfwer many 
intentions than that commonly uied. The plan is fomewhat 
fimilar to nonius’s divifion of the circle ; but before I explain 
myfelf farther it may be proper to lay down a few general 
rules on which we may found a comparifon. 
The perfection of any machine confifts in accomplifhing the 
end propofed in a manner the mod effectual, the mod: expedi- 
tious, and the leaft cumberfome poflible. In order to attain 
this end the following things are required. 
1. That the ftrength of the feveral parts of the engine be fo 
adjufted to the force they are intended to exert, as that they 
fhall not break under the weight they ought to counteract, nor 
yet encumber the motion by a greater quantity of matter than 
is neceffary to give them a proper degree of flrength. 
2. That the increafe of power, by means of the machine, 
be fo regulated, that while the force we can exert is thereby 
rendered adequate to the effeCt, it may not be retarded in pro- 
curing it more than is abfolutely neceffary. 
j 
3. That 
