47 o Mr. smeaton on Mechanic Power . 
pufh at it, he will find it very refilling to motion at firfl ; 
but, by continuing the impulle,he will gradually get it into 
motion, and having nothing to refill it but the air, he will, 
by continuing his efforts, at length get it to roll almoft as 
fall as he can run. Suppofe now, in the firfl minute he 
gets it rolled through a fpace of one yard ; by this motion, 
proceeding from reft (fimiiar to what happens to falling 
bodies) it would continue to roll forward at the rate of 
two yards per minute, without further help; but fup- 
pofing him to continue his endeavours, at the end of ano- 
ther minute he will have given it a velocity capable of 
carrying it through a fpace of two yards more, in addition 
to the former, that is, at the rate of four yards per mi- 
nute ; and at the end of the third minute, he has again 
added an equal increafe of velocity, and made it proceed 
at the rate of fix yards per minute; and fo on, increafing 
its velocity at the rate of two yards in every minute. The 
man, therefore, in the fpace of every minute exerts an 
equal impulfe upon the ball, and generates an equal in- 
creafe of movement correfpondent to the definition of 
Sir Isaac newton. But let us fee what happens befides : 
the man, in the firft minute, has moved but one yard 
from where he fet out ; but he mull in the fecond minute 
move two yards more, in order to keep up with the ball ; 
and as he exerted an impulfe upon it, fo as at the end of 
fecond minute to have given it an additional velocity of 
the two yards, he muft alfo in this time have gradually 
changed its velocity from the rate of two yards per mi- 
nute to that of four, and the fpace, that he will of confe- 
3 quence 
