VOL. XXX.] PHILOSOPHICAL TRANSACTIONS. 429 



Esq. F. R. s. and another person, who all agreed in their observations of the 

 time, which they made each with a half second pendulum. 



The following table shows the marks, weights, and diameters, of the several 

 balls, in 3 columns. 



N. B. The polar and equatorial diameters of the glass balls being different, I 

 have set down a mean diameter for each of them ; the true diameters are thus, 

 of D 4 and 3.8, of e 5.6 and 5.25, of f 5.7 and 5.4 inches. 



By Galileo's theory, the lead, which was 44-^ in falling, must fall 4 feet the 

 first -i-% or l6 feet the first second, which amounts to 324 feet in 44-^ But 

 since the sound of the ball, as it struck the bottom, by which we reckoned our 

 time, had 272 feet to move, we must abate a quarter of a second nearly, sup- 

 posing sound to move I mile in 4-^*, which will take away 35 feet, that the body 

 must have fallen in the last quarter of a second, and reduce the number of feet 

 to 289 ; so ^^^^ ^^^ ^^^^ ^^^^ h^^^ °^^y fallen 1 7 feet short of the theory, which 

 must be attributed to the resistance of the air. 



The large glass ball in the 6 seconds of its fall, would in a vacuum go through 

 576 feet; but taking away the last quarter of a second, or 47 feet, for the 

 motion of sound, it must only fall 529 feet in vacuo. Now since it fell only 

 272, there have been 257 feet taken off fi-om the fall by the air's resistance. 



Likewise the pasteboard ball, in 64- seconds, must have fallen 676 feet; but 

 deducting the last quarter of a second, or 5 1 feet, for the motion of the sound, 

 there remains only 625 feet for its fall in vacuo. But as it fell only 272 feet, 

 we must allow a retardment of 353 feet for the resistance of the air. 



At a medium we may call the weight of the glass ball 5 oz. Troy, and its 

 diameter 5^ inches; and the weight of the pasteboard ball 2 oz. Troy, and a 

 little more than 5 inches diameter. All the lead balls fell within about a foot 

 of each other, and made an impression in the boards of about one-third of 

 their depth. The barometer stood at 30.1 inches, and the mercury was very 

 convex, and therefore inclined to rise still. 



