A PENDULUM FOR THE REDUCTION TO A VACUUM. 
455 
Twenty-first set . — Results with the 2-inch cylinders, placed edgeways, at the 
end of the long brass rod. 
Thickness 
of the 
cylinder. 
No. 
n 
Weight of 
adhesive 
air. 
Weight due 
to cylinder 
alone. 
inch. 
o-oo* 
43 
4-083 
1-484 
0-18 
83 
2-771 
1-219 
0-149 
0*50 
84 
2-208 
1-239 
0-353 
Twenty-second set . — Results with the thin brass discs, placed edgeways, 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-oo* 
2- 07 
3- 01 
43 
85 
86 
4-083 
4-291 
4-472 
1-484 
1-588 
1-675 
0-091 
0-168 
These experiments confirm the remark already made, that the sides of the 
moving body drag with them very little of the air which has so remarkable an 
effect on the pendulum. In this last set, the discs were placed (as in the 18th 
set), at 8 tenths of an inch above the centre of oscillation. In making the 
computations for the weight due to the disc alone, this has been allowed for : 
and I would also observe that the whole effect of the rod has been used in 
those computations ; as it is evident that the position of the disc does not 
obstruct any part of its action on the air. 
General results of the Additional Experiments. 
I must here close the account of these additional experiments, which have 
been pursued up to the latest moment that could be conveniently spared by 
the printer ; as I was desirous of communicating at once all the information 
I could procure on this interesting subject : and which consequently leaves me 
only time to offer a few brief remarks on the results obtained. 
* See the first note in page 443. 
3 N 2 
