[ I0 3 J 
XXV. "The Properties of the mechanic Pow- 
ers demonjt rated , with fame Obfervations 
on the Methods that have been commonly 
ufed for that Purpofe : in a Letter from 
Hugh Hamilton, D. D . F.R.S . and 
Fellow of Trinity College, Dublin, to 
Matthew Raper, Efq\ F. R. S. 
SIR, Trinity College, Dublin, 13 July, 1762. 
Read April 2i, X" Have here ventured to fend you fome 
763^* A remarks on the methods that have been 
commonly ufed in treating of thofe engines that are 
called the mechanic powers : and alfo an account of 
the principles on which, I think, we may bed; explain 
their nature and manner of adting. 
The many ufeful inftruments that have been fo 
ingenioufly invented, and fo fuccesfully executed, 
and the great perfection to which the mechanic arts 
are now arrived, would naturally incline one to think 
that the true principles on which the efficacy and ope- 
rations of the feveral machines depend, mud long 
fince have been accurately explained. But this is by 
no means a neceffiary inference: for, however men 
may differ in their opinions about the true method of 
accounting for the effeCts of the feveral machines, yet 
the pradtical principles of mechanics are fo perfectly 
known by experience and obfervation, that the artift 
is thereby enabled tocontrive and adjuftthe movements 
of 
