222 = Mr Bryson on Baily’s Compensation Pendulum. 
This eminent astronomer has not taken into account any 
influence on his pendulum-rod by hygrometric change, an 
effect much more appreciable in a deal-rod pendulum, and, 
therefore, detrimental to its usefulness, than the mere ther- 
mal effect. The method adopted for the purpose of rendering 
the rod insensible to a humid atmosphere, is first to deprive it 
of its natural and acquired moisture by baking ; and, secondly, 
to prevent its absorption either of air or moisture, by long 
immersion in copal varnish. This covering is found to pre- 
serve more effectually the wood from such influences than any 
hitherto tried. The apparatus employed is very simple and 
convenient, as it can perform the operation of baking in less 
than an hour. It consists of a piece of clock-work A, giving a 
rotatory motion, by means of a spring, to the hollow cylin- 
drical tube B, supported by two friction-wheels, on which it 
revolves, as seen at the left side of the figure. Cis a flexible 
pipe supplying gas to a tube below, marked D D; this tube 
is pierced by ten or twelve small apertures, from which the 
gas burns and heats the upper tube B, containing the pendu- 
lum-rod. This upper tube is also pierced with a series of holes 
CNT 
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for the purpose of permitting the escape of the moisture of 
the rod, these apertures being placed between the jets of 
gas so as to prevent the heat acting on the contained wood. 
Wire-gauze was tried above the gas-tube D D with good effect, 
as it caused the complete combustion of the gas, and there 
was, consequently, no deposition of carbon on the revolving 
tube, which, when deposited to any great extent, robbed it of 
much heat. The pendulum-rod, before baking, is to be finish- 
ed in all its parts, with screw below and suspending-tube 
above. This is a necessary precaution, as if baked before 
mounting, moisture would be absorbed at the ends, thus ren- 
dering the instrument less perfect. When the rod is finished, 
it is to be placed in the revolving tube B, and exposed to 
the flame until no moisture can be perceived issuing from the. 
