MR. BAILY’S DESCRIPTION OF A NEW BAROMETER. 
441 
steps of a common landing place, abutting on the river, are liable to settle ; and in 
course of time to be altogether removed, for the purpose of repairs. It therefore be- 
came desirable, on more accounts than one, to connect together the two marks at 
London and Waterloo Bridges by direct levelling. This has recently been effected, 
at the request of the Council of this Society, by the direction and under the superin- 
tendence of Sir John Rennie, who readily undertook the determination of this point. 
In his letter on this subject, dated October 18, 1837, he says, “After repeated trials 
“ (the greatest variation of which did not exceed T v of an inch) I find that the difference 
“ is 3 feet T65 of an inch : that is, the mark on Waterloo Bridge is 3 feet T65 of an 
“ inch above that on the New London Bridge fixed by Captain Lloyd.” 
The height of the cistern of the present barometer above the floor is 175 foot: 
therefore adding all these several quantities together, namely, 
19-000 
62-410 
10-754 
3-138 
1-750 
97052 
we have, in round numbers, 97 feet for the height of the mercury in the cistern of this 
barometer above the mean level of the sea. 
One word more before I close this paper, as to the propriety of the position of the 
several meteorological instruments of this Society ; on which, comments have occa- 
sionally been made. With respect to the barometer, I am not aware that any objec- 
tion can be offered ; and as to the hygrometer, the observations have been found, by 
recent trials, not to differ materially from some expressly made in another position, at 
King’s College, which was considered to be more favourable for such experiments. 
It therefore only remains to speak of the external thermometer and of the rain-gauge ; 
of which all that can be said on the subject would be merely a repetition of what 
was justly said sixty years ago by Mr. Cavendish on a similar occasion (Philoso- 
phical Transactions, 1776), namely, “that, on the whole, the situation is not alto- 
“ gether such as could be wished, but is the best the house affords.” 
