6l1 PHILOSOPHICAL TRANSACTIONS. [aNNO 17]0. 



is derived from our analysis of the problem concerning the length of curve lines, 

 is the same with that proposed in the Philos. Trans, for the year 17O8. Being 

 wholly intent about the analysis, I did not observe the coincidence of the curve 

 proposed with that which was found, till Mr. John Bernoulli informed me of 

 it, in his letter to Mr. Wm. Burnet, F. R. S. by which also that learned man 

 was pleased fully to satisfy all my objections against his creeping motion ; as I 

 now freely acknowledge, from that pure regard which I bear to truth. 



Experiments concerning the Time required in the Descent of several Bodies, of 

 different freights and Magnitudes, in Common Air, from a certain Height, 

 By Mr. Fra. Hauksbee, F. R. S. N*' 328, p. 196. 



To make these experiments accurately, I devised the following appartus, to 

 obtain exactly the time of the bodies' descending. At the height from which 

 the balls were to be dropped, I fixed a contrivance in form of a trough, in all 

 about 4 feet long ; and the end of it, on which the balls were laid, was loose, 

 swinging on 2 pins at the extremity. This loose end was supported by a thin 

 piece of board, which slid under it through a groove from the other part of 

 the board : t© this sliding board was fixed a string, connected to a small wire 

 reaching to the bottom of the descent, where the wire had a communication 

 with a contrivance, to give motion to a pendulum vibrating half seconds. Now 

 when this sliding board was drawn from under that part of the trough on which 

 the balls were placed, the string thereby became so much shortened, as to move 

 the limb of that contrivance at bottom, which dropped the pendulum at the 

 same instant of time that the balls began to descend. 



Exper. I. — The first experiment was with two balls : one of them a thin glass 

 bubble, filled with quicksilver; its diameter 8 tenths of an inch, and its weight 

 840 grains; the other ball was of cork, its diameter was 2-jV inches, audits 

 weight 120 grains. When these balls were dropped, the pendulum made 8 

 vibrations, just as the quicksilver ball struck the ground, and 8 more were re- 

 peated before the cork arrived at the same place. The pendulum vibrated half 

 seconds precisely. 



Exper. II. — I took a quicksilver ball, much of the same weight and diameter 

 as before; the other was a thin glass bubble, its weight 493 grains, and dia- 

 meter 4tV inches. For these, when they came to descend, the pendulum made 

 just as many vibrations as in the last experiment; that is, the quicksilver ball 

 struck the ground at 8 vibrations, and the other just at the end of 16. 



Exper. III. — ^The quicksilver ball used in this experiment, was also much of 

 the same weight and diameter as before: the other ball was of glass, its weight 



