412 
MR. BAILY ON THE CORRECTION OF 
have calculated the specific gravities of each of these hollow pendulums as 
follows ; to which also I have annexed the weights. 
No. Spec. grav. Grains. 
15 = 2-536 .... 8497 
16 = 2-623 .... 8922 
17 = 2*561 .... 8622 
18 = 2-649 .... 9048 
After the experiments with these tubes were completed, I caused the inner 
sliding tube to be filled with lead, as mentioned in the preceding article: and 
this solid cylinder could be readily put into and taken out of the outer tube, 
at pleasure. And when the experiments with this solid cylinder were com- 
pleted, a new top piece was made to the outer tube, which was closely sol- 
dered on : a new bottom piece was also made, to screw on and off, which, by 
the application of an oiled leather to the screw, might at any time be rendered 
hermetically sealed. 
No. 19 is the tube thus hermetically sealed. The inner sliding tube having 
been taken away, the weight was reduced to 7250 grains : the specific gravity 
I found to be 2*233*. The hollow portion of the cylinder now contains 3 - 255 
grains of air. 
No. 20 is a lens of lead, 2-06 inches in diameter ; 1 inch thick in the 
middle, and having a flat circumference about a quarter of an inch wide. 
This lens was tapped with a screw-hole on one of its protuberant sides, and 
was supported by the same iron wire and knife edge as above described : the 
position of the lens was consequently horizontal. Its specific gravity with the 
screw I found to be 1 1'254 ; and they weighed 6505 grains. 
proximately so, in the other cases,) the centre of oscillation of the included air will coincide with that 
of the metal ; and the centre of oscillation of the compound mass will therefore coincide with that of 
the metal alone. 
* When the bottom piece of this tube was loosely screwed (so as to admit the free passage of the 
air under the exhausted receiver,) it might he considered as a pendulum similar to No. 18, with the 
specific gravity of 2 ’233 : and when the bottom piece was wholly taken away, it might be considered 
as a pendulum similar to No. 17. Experiments were made with the tube under these circumstances, 
to which I shall allude in the sequel, fully confirming the results of the former ones. In the latter 
case, when the bottom piece was taken away, the weight was reduced to G744 grains ; and the spe- 
cific gravity was computed to he 2'042. The solid sliding cylinder is also adapted to this new state 
of the tube ; but at present I have not made use of it, in this way. 
