430 PHILOSOPHICAL TRANSACTIONS. [ANNOjyiQ. 



A further Account of Experiments made for the same Purpose, viz. the Resist- 

 ance of the Air. By the same. N° 302, p. 1075. 



Having found by the former experiments that thin glass balls, and even balls 

 of pasted paper, were too heavy to make so considerable a difference between 

 the time of their fall and the fall of leaden balls, that it might be easily observed; 

 I contrived a way to make dried hog's bladders perfectly round, by blowing 

 them, when moist, within a strong spherical box of lignum vitae, and letting 

 them dry in the box before I took them out, which I did by opening the box 

 that screwed in the middle, and had a hole in the pole of one of its hemispheres 

 to let the bladder pass through, in order to tie it after blowing; and some few 

 small holes all over the box, that in blowing no air might be confined between 

 the inside of the box and the bladder, so as to hinder it from taking a spherical 

 figure. Besides, I took off the ends of the ureters, the fat and a great deal of 

 the upper coats of the bladders, before I blowed them in the box to render 

 them still lighter. 



The bladders 1 used were some of the thinnest I could find ready blown at a 

 druggists, which I moistened in water, taking care to leave none in the inside. 

 I chose those rather than fresh ones, which in drying would have stuck so fast 

 to the inside of the box, that it would scarcely have been possible to have got 

 them out without tearing. 



Having prepared 5 bladders as above, I took them up to the upper gallery in 

 the lantern on the top of the cupola in St. Paul's church, and there by a con- 

 trivance, which I shall describe, I let them fall by one at a time, together with 

 a leaden ball of about 2 inches diameter, and weighing 2 lb. Troy; and I took 

 notice of the time of the fall of each bladder, knowing by former experiments 

 that the balls are about 4^- seconds, or a little longer time, in falling the same 

 height, which is 272 feet. 



The following table, consisting of 5 columns, gives in the first the marks oi 

 the bladders; in the next their diameters; in the 3d their weights in grains 

 Troy; in the 4th the times of their fall in second minutes of time; and in the 

 5th the difi^erence of time between the fells of the leads and of each bladder, 

 taken below by the president. Dr. Halley, Dr. Jurin, Martin Folkes, Esq. and 

 Mr. George Graham, the clock-maker. The time was taken above with Mr. 

 Graham's chronometer, and below with the same instrument, and three half- 

 second pendulums, all which agreed very well together. 



The experiments having been made twice over, the table is twice set down: 



