452 
MR. BAILY ON THE CORRECTION OF 
Eighteenth set.— Results with the thin brass discs placed near the centre of 
oscillation of the long brass rod*. 
Diameter 
of the 
disc. 
No. 
n 
Weight of 
adhesive 
air. 
Weight due 
to disc alone. 
inches. 
O-OOf 
43 
4-083 
1-484 
2-07 
75 
7-439 
3-111 
1-405 
3-01 
76 
14-362 
6-511 
4-185 
4-00 
77 
27-033 
12-873 
9-367 
In these experiments the value of n, and also the weight of air dragged by 
the pendulum increase as the diameter of the disc increases. If we examine 
the values in the last column (in computing which, the quantity of air dragged 
by the rod has been assumed of a different value in each case, or proportionate 
to the length of the rod, minus the diameter of the disc), we shall find that the 
quantity of air dragged by these thin discs, is also nearly in the ratio of the 
cubes of their diameters : and the general expression for the amount of the 
same will be nearly 
grains. 
r + 0T49 d 3 
r and d denoting the same quantities as before. 
With a view of following up this inquiry relative to the discs, I caused the 
same brass rod to be tapped with 3 other screw holes: one at 5*1 inches from 
the knife edge, being the highest point to which I could fix anything; another 
at 3(H) inches from the knife edge, or near the centre of gravity of the rod ; 
and the other at 5/’3 inches from the knife edge, or near the lower end of the 
rod. The thin brass disc, 2*07 inches in diameter, was then successively fast¬ 
ened to the rod, at each of these distances, and swung in the same manner as 
in the preceding set, with the flat sides opposed to the line of motion. The 
following are the results ; including that of No. 75 given in the preceding set. 
* Owing to some mistake all these discs were placed 8 tenths of an inch above the centre of oscil¬ 
lation. This is allowed for in the computations for the weight due to the disc alone. 
t See the first note in page 443. 
