PHYSICAL ann LITERARY. 3 
periments se ufelefs lumber, if we are hot. 
to reafon about them, nor draw any con{e- 
quences fromthem. In all our operations, we 
may havean eye to theory: nay we mutt have 
it; for fuch is the conftitution of eur mind. 
‘Theory becomes only a fource of error, when 
we indulge in it too much, or attach ourfelves 
_ to it beyond what facts and experiments can 
juttify, In fhort, theory is vain without ex- 
periments, and experiments are beft under- 
{tood by applying them to theory. 
ahs NatTurat philofaphy, it muft be acknow- 
ae ledged, is far from being ripe for firm and 
. lafting theory. But we have facts and expe- 
riments in great abundance, to be a founda- 
tion for theoretical fketches ; which may be 
.fafely indulged, provided they be done in fo 
flight a manner, as to leave the mind free 
from any wrong bias. Tho’ we haye not ma- 
terials for a regular building, there is nothing 
to hinder us to venture upon a model, 
AtmostT every author who treats of the 
laws of motion, has thought it incumbent up- 
’ on him to fet out witha definition of motion. 
And, in a thing fo fimple, it may appear 
{trange to find fuch a yariety of definitions : 
__ whence one thing may be gathered, that none 
; a of 
