C r +3 ] 
a power of one ounce, more than what is juft ne- 
ceftary to counterbalance a weight of y pound, will 
raiie it with as great a degree of velocity, as 2 ounces 
over and above what is juft neceftary to overcome the 
refiftance from fridtion. So that it muft require an ad- 
ditional power in proportion, to overcome the refiftance 
from fridtion, with the fame degree of velocity, that 
it may be neceftary to raife the weight. 
It is not imagined that thefe experiments ftiould 
determine the exadt quantity of fridtion proceeding 
generally from weight, or preffure ; which probably 
can never be afcertained by any experiments, however 
accurate ; for even in engines of equal dimensions, and 
loaded with equal weights, the quantities of fridtion 
may be very unequal, from circumftances differing, . 
which arefometimes imperceptible; fuch as the firm- 
nefs, elaft icity, roundnefs and fmoothnefs of the parts 
rubbing on each other; particularly the roundnefs, and 
fmoothnefsof the gudgeons, orpevets, which, in large 
engines, are feldom turned true, or polifhed. But it ap- 
pears from thefe experiments, that the quantity of fric- 
tion in large engines may reafonably be eftimated at 4. 
the weight, or preffure, on the rubbing parts ; al- 
though in fuch as are ffnall, and finifhed with exadt- 
nefs, the quantity may probably be about 4. 
It is evident that the quantity of fridtion in any 
engine, is equal in its oppofition to a certain portion 
of weight, or preffure on the parts rubbing on a 
dead furface. And, altho’ gravity is an adtive 
principle always tending to a center, and fridtion, 
a kind of vis inertiae in oppofition to motion, yet it 
may be confidered mechanically as fo much weight 
which requires a power to overcome its refiftance, in 
a ratio- 
