REPORT OF THE COUNCIL. 
xli 
(Copy.) 
“ Clapham Common, 2nd June, 1854. 
“ Sir,— In reference to my letter of 3rd April, I have now to acquaint 
you, that the Committee have decided on the barometer which they con- 
eider most applicable for marine observations, one of which I forward for 
inspection. 
“In selecting the form of marine barometer best adapted to the purpose 
ot making observations at sea, the Committee have endeavoured to combine 
convenience and ceconomy with accuracy, durability, and simplicity in con¬ 
struction and adjustments. A barometer which has been constructed by 
Mr. Adie appears to them to fulfil those conditions in a satisfactory manner. 
Its action at sea has been tested under their superintendence by Mr. Welsh 
on two occasions, one on a voyage to Leith and back, anil subsequently to 
the island of Jersey. The general conclusion arrived at in those trials is, 
that in order to reduce the pumping of the mercury within convenient 
limits, it is necessary to have the tube contracted to such an extent that the 
mercury will take about twenty minutes to fall from the top of tin- tube to 
the height indicating the true pressure of the atmosphere at the time. From 
comparisons made at Kew with the standards there, it lias been found that 
owing to this contraction in the tube the absolute freedom of' the mercury 
is to a small extent interfered with; ns the motion of the mercurv in the 
standard barometer is always a little in advance of the rnariue barometer; 
that is, when the mercury is rising, from increasing pressure of the atmo¬ 
sphere, the marine barometer is a little lower than the standard, ami. mi the 
contrary, when the mercury is falling, the marine barometer is a little higher. 
J he amount of this retardation is however very small, something less than 
PJp.h of an inch, and from its being in opposite directions in a rising and 
tailing barometer, will produce no error in the mean height of the barometric 
column; it will, however, to some extent mark the smaller changes, such as 
the hourly variations. It should lie remarked, however, flint tin. mntinn r,F 
(Copy.) 
Sir F. Beaufort, F.R.S., Uydrographer, 
&c. &c. &c. Admiralty.” 
“ Chairman of Kcw Committee, 
British Association.” 
