224 Mr Bryson on Baily'’s Compensation Pendulum. 
baked and unvarnished, will lose on its rate per day 3’.53 
by a change in the humidity of the atmosphere, equivalent 
to 19°.4 of Leslie’s hygrometer. 
The third experiment possesses little interest further than | 
verifying the first, and shewing the tendency of the wood to 
regain its former condition, when the humid was exchanged 
for a drier atmosphere. 
We may now contrast with the above the effect produced 
by baking and varnishing. 
Accordingly, the fourth and fifth experiments exhibit the 
rate and the conditions under which it was obtained, after the 
rod had been baked, varnished, and properly dried as de- 
scribed. In these two experiments we have a mean differ- 
ence of 19.6 degrees of the hygrometer, while the barometer 
exhibits a mean difference of (328 inches, giving a correc- 
tion = + 0”.098 to be applied to the clock’s rate in the cellar, 
which makes it = 2’.758, this quantity being corrected, as 
before, for diminution of gravity, makes the corrected rate 
in.the cellar = 2’.703. 
From these observations the change of rate pnciieni by 
hygrometric influence, is reduced by this method of treating 
the pendulum rod from a variation of 3’.53 to 0’.37 of a second 
per day; a quantity which in most time-keepers would be 
entirely disregarded. We have, therefore, a pendulum nearly 
perfect at a cost very little exceeding those attached to ordi- 
nary clocks, and fitted for most general purposes to which 
astronomical regulators are usually applied.* 
The quantity of moisture thrown out by the baking process 
is very considerable, a rod weighing, before heating, 900 
grains, lost 130 grains, a second 152 grains, a third 107 
grains of moisture. These rods were cut from the library 
shelves of the Karl of Stair, fitted up in his house in the 
High Street. They must have been in that situation for nearly 
two centuries, and would certainly be called well-seasoned ; 
yet we see in the great amount thrown out, an affinity for 
moisture Doseensed by WBey few solid substances. 
* Among many Finis to beitlonien eminent in science, we may 
state six were observed by Sir Thomas Brisbane and the late lamented 
Professor Henderson, who have both, from an experience of two years, 
spoken highly of the performance of this pendulum. 
