430 
MR. BAILY ON THE CORRECTION OF 
contrary to what takes place with all the preceding convertible pendulums ; 
and contrary to the theory on this subject recently developed by some excel- 
lent mathematicians. 
Twelfth set . — Results with Clock 'pendulums, suspended hy springs. 
39) Mercurial. 
Leaden cylindrical bob. 
40) Cylindrical rod. 
41) Flat rod. 
Exp. 
n 
Exp. 
n 
Exp. 
n 
189—190 
191—192 
193 — 194 . 
195—196 
Mean = 
2-441 
2-316 
2-350 
2-267 
201—202 
203—204 
Mean = 
2-562 
2-616 
197—198 
199—200 
Mean = 
2-794 
2-860 
2-343 
2-589 
2-827 
Besides these clock pendulums there is another kind, not here enumerated, 
consisting of a lenticular shaped bob, of some heavy metal, suspended either 
by a single rod, or by several compensation rods ; in which latter case, it is 
called the gridiron pendulum. As my vacuum apparatus was not sufficiently 
large to receive a pendulum of this kind, I cannot throw any light on the pro- 
bable value of n in these cases. But, as the bob of such a pendulum is not 
much unlike the convertible pendulum of Captain Kater, when deprived of its 
tail pieces, (see the description of the pendulum No. 23 in this arrangement,) 
we may form some estimate of the probable value of n, when the pendulum is 
suspended by a single rod. In the case of the gridiron pendulum however, it 
may be a matter of doubt whether the air between the vertical rods may not 
diminish their specific gravity, when considered as a vibrating body. With 
respect to the leaden cylinders attached to the wooden rods, it will be seen 
from the experiments with the pendulums No. 40 and 41, that in the case of 
the thin flat rod, the factor is greater than with the cylindrical rod : contrary 
perhaps to what might have been anticipated*. 
* This is confirmed by a repetition of the experiment with the same cylinder, and with rods of the 
same form as the present ones, but of different materials. The difference was, as in the present case, 
about '200. 
