Dr, Wollaston’s Lecture 
1*5 
would be in the ratio of 2 to 1 , and the squares of the velo- 
cities in proportion to the quantities of labour from which 
they originated, or as 4 to 1 ; and if the forces acquired by 
their descent were employed in driving piles, their more 
sudden effects produced would be found to be in that same 
ratio. 
This species of force has been, first by Bernouilli and 
afterwards by Smeaton, very aptly denominated mechanic 
force ; and when by force of percussion is meant the quantity 
of mechanic force possessed by a body in motion, to be esti- 
mated by its quantity of mechanic effect, I apprehend it 
cannot be controverted that it is in proportion to the magni- 
tude of the body and to the square of its velocity jointly. 
But of this quantity of force Newton no where treats, and 
has accordingly given no definition of it. If, after defining 
what he meant by the quantitas acceleratnx, and quantitas 
matrix , he had had occasion to convey an equally distinct idea 
of the quantitas mechanica resulting from the continued action 
of any force, he might, not improbably, have proceeded 
conformably to the definition given by Smeaton, and have 
added 
——quantitas mechanica est mensura proportionalis spatio 
per quod data vis motrix exercetur ; 
or, if speaking with reference to the accumulated energy 
communicated to a body in motion, 
proportionalis quadrato velocitatis quam in dato 
corpore generat. 
But, if we attend to the words of his preface to the first 
edition of his Principia , he evidently had no need of such a 
definition ; 
