Mr Bryson on Baily’s Compensation Pendulum. 223 
apertures ; by moving the rod backwards and forwards in 
the tube at intervals of a few minutes, it will be regularly 
heated throughout its whole length. While hot, it is then 
plunged into a tube filled with copal varnish and allowed to 
remain during twenty-four hours. When removed, the var- 
nish must be slowly evaporated in a warm situation, and, 
when dry, is ready for use. 
For the purpose of ascertaining how far the process was 
successful in rendering the rod insensible to humidity, an un- 
baked and unvarnished pendulum was tried, the rod was 3 of 
an inch diameter, and had a leaden cylinder 14.3 inches long. 
The clock, to which it was attached, was set a-going early 
in April 1842, and on the 9th its rate was observed gaining 
9 seconds per day. It was placed in the front of the shop in 
Princes Street, where it was exposed to a dry atmosphere 
during ten days; the mean indication of the hygrometer 
(Leslie’s) being 29.3 degrees, the mean daily rate of the clock 
being 9”.5 gaining. The pendulum being fixed, the clock was 
removed, on the 19th, to a cellar 10 feet below its former 
situation, when its rate was observed, in a few days, to have 
changed to 6".5 gaining per day, the hygrometer shewing 8 
degrees only of dryness ; in this situation it remained during 
ten days, its error always observed, as in the first experiment, 
at noon. The mean result of these ten days exhibited a gain- 
ing rate of 6".1 per day, while the mean indication of the 
hygrometer was 9.9 degrees of dryness. Tliese observations 
will be more clearly understood by reference to the annexed 
tables, which contain the details of the experiments. In the 
experiment now under consideration, the pendulum was sup- 
posed to be nearly compensated ; no correction is, therefore, 
required for the thermal differences shewn in the tables. 
The mean range of the barometer, during the period of the 
two first experiments, was 0.256 inches, giving a correction, 
for difference of density, = — 0’.076 to be applied to the 
clock’s rate in the cellar, we have then the rate = 6”.024. 
_ This rate will be still further reduced if we correct it for the 
difference of height, which, being 10 feet, gives a correction 
= — 0’.055 for diminution of gravity, making the corrected 
rate of the clock in moist atmosphere = 5’.969 gaining per 
day, 
It is, therefore, evident that a dry well-seasoned rod un- 
