Experiments upon Gnnpowder. 61 



If now a computation be made according to the 

 method laid down by Sir Isaac Newton for compress'ed 

 fluids, it will be found that the resistance to this bullet 

 was not less than 8| Ibs. avoirdupois, which is some- 

 thing more than 660 times its weight. But Mr. Robins 



O o 



has shewn, by experiment, that the resistance of the air 

 to bodies moving in it with very great velocity is near 

 three times greater than Sir Isaac has determined it, and 

 as the velocity with which this bullet was impelled is 

 considerably greater than any in Mr. Robins's experi- 

 ments, it is highly probable that the resistance in this 

 instance was at least 2000 times greater than the weight 

 of the bullet. 



The distance from the mouth of the piece to the pen- 

 dulum, as we have before observed, was 12 feet; but, 

 as there is reason to think that the blast of the powder, 

 which always follows the bullet, continues to act upon it 

 for some sensible portion of time after it is out of the 

 bore, and by urging it on counterbalances, or at least 

 counteracts, in a great measure the resistance of the air, 

 we will suppose that the resistance does not begin, or 

 rather that the motion of the bullet does not begin to 



D 



be retarded, till it has got to the distance of two feet 

 from the muzzle. The distance, therefore, between the 

 barrel and the pendulum, instead of 12 feet, is to be 

 estimated at 10 feet; and as the bullet took up about 

 T"92" P art f a secon d in running over that space, it 

 must, in that time, have lost a velocity of about 335 

 feet in a second, as will appear upon making the com- 

 putation, and this will very exactly account for the ap- 

 parent diminution of the velocity in the experiment; 

 for the difference of the velocities, as determined by the 

 recoil and by the pendulum, = 2109 J 7^3 == 34^ 



