PHYSICAL ann LETERARY. 77 
velocity is another.. A’ given body moved 
with a great velocity, is one effect; and when 
moved with a lefs velocity, it is a different ef- 
fect. The old principle feems to apply well 
enough in this cafe, that effects are propotti- 
onal to their caufes. 
Ir. muft be confeffed,. that authors -in- 
treating of the zvertia of matter, and of its 
_ refiftance to motion, are very apt to exprefs 
themfelves in terms that import a real activi- 
ty; and which, if ftritly ‘underftood, are 
inconfiftent with zertia. Thus, when a per- 
fon in a boat pulls a rope that is faftened to 
the fhore, it is commonly faid, that the man 
acts upon the fhore in one direction, and that 
the fhore, by its reaction in the oppofite di- 
rection, pulls the man and boat towards it. 
Yet, notwithftanding fuch expreffions, will 
any one ferioufly maintain, that the ground 
__ has an active power to produce any fuch ef- 
fect? It is evidently the force of the man 
- extending himfelf, that draws the fhore with 
_ his hands one way, and at the fame time 
_ puthes the veflel with equal force with his 
- feet the oppofite way. In like manner, if a_ 
perfon ftanding in a boat, pufhes againft the 
ground with a pole, it is not really the rea- 
Be > ee tion 
