upon Gun-powder , &c. 291 
-will be much ftrengthened when we confider how great the 
refiftance is that the air oppofes to bodies that move very fwiftly 
in it, and that the bullets in thefe experiments were not only 
projected with great velocities, but were alfo very light, and 
confequently more liable to be retarded by the refinance on that 
account. 
To put the matter beyond all doubt, let us fee what the re- 
finance was that thefe bullets met with, and how much their 
velocities were diminifhed by it. The weight of the bullet (in 
the 85th experiment) was 90 grains; its diameter was 0,78 of 
an inch, and it was projected with a velocity of 2109 feet in a 
fecond. 
If now a computation be made according to the method laid 
down by Sir Isaac newton for compreifed fluids, it will be 
found, that the refiftance to this bullet was not lefs than 8f 
lbs. avoirdupois, which is fomething more than 660 times its 
weight. But Mr. robins has fhewn, by experiment, that 
the ref fiance of the air to bodies moving in it with very great 
velocity is near three times greater x than Sir Isaac has 
determined it, and as the velocity with which this bullet was 
impelled is conflderably greater than any in Mr. robi-n s’ s expe- 
riments, it is highly probable, that the refiftance in this in- 
fiance was at leaf; 2000 times greater than the weight of the 
bullet. 
The diftance from the mouth of the piece to the pendulum,., 
as we have before obferved, was 1 2 feet but,_ as there is rea- 
fon to think, that the blaft of the powder, which always fol- 
lows the bullet, continues to act upon it for fome fenfble fpace 
of time after it is out of the bore, and by urging it on coun- 
ter-balances, or at leaf; counter- acts in a great meafure the 
refiftance of the air, wie will fuppofe, that the refiftance does; 
not 
x 
