MR. BAILY’S DESCRIPTION OF A NEW BAROMETER. 
439 
I have here given may create some doubt respecting the accuracy of the past, yet I 
am persuaded that the system now pursued will inspire more confidence for the future. 
It is on this account that I have entered thus at large on the subject: trusting that 
what I have here stated will not only tend to preserve for the future a more correct 
and uniform system, but also justify the Council in directing that the register should 
henceforth contain the daily observations uncorrected, and thus prevent the possibility 
of any similar confusion and mistakes hereafter. 
I shall now say a few words respecting the height of the barometer above the mean 
level of the sea ; a subject of much interest to many persons engaged in various pur- 
suits, but which appears, from the notes attached, at different periods, to the meteoro- 
logical journal of this Society, to be involved in some confusion and uncertainty. 
Thus, prior to the year 1823, the cistern of the barometer is said to be 81 feet above 
the level of low- water spring tides at Somerset House ; but without any information 
how this was connected with the sea. From 1823 to 1825, both inclusive, it is said 
to be 100 feet above the same level. And from 1826 to 1836, both inclusive, the 
above indication is omitted, and the height is said to be 83 feet 2^ inches above a fixed 
mark on Waterloo Bridge; or “above the mean level of the sea (presumed about) 
95 feet.” The discordance between the 81 feet and the 100 feet is easily accounted 
for by the fact that the old barometer, prior to 1823, was fixed up in the Council-room 
of the Society, or the contiguous ante-room : but when Mr. Daniel’s barometer was 
finished, at the end of the year 1822, it was fixed up in the closet adjoining the library, 
on the floor which is immediately over the Council-room : the assumed difference in 
the elevation of the two floors (namely, 19 feet) having since been ascertained to be 
correct. 
With respect to the new reference of altitude, namely, the fixed mark at Waterloo 
Bridge, much doubt has frequently been expressed about its existence, since no person 
had been able to discover it. The fact is that there is no mark , in the common ac- 
ceptation of the term ; but the intended reference is nevertheless more conspicuous, 
more durable, and more convenient than any mark that could have been inscribed by 
hands. This standard mark, or level, was fixed on by Mr. Bevan in the year 1827, 
at the request of the Council of this Society : and the same gentleman also ascertained 
the difference of level between that mark and the floor of the council room. As his 
Report on the occasion has never yet been made public, and will throw the best light 
on the subject, as well as be interesting to many persons, I shall here subjoin his 
letter to the Council, detailing the whole circumstances of the case. 
“ Gentlemen, — Pursuant to the order I had the honour to receive at the close of 
“ your last session, I have selected a permanent and definite point of reference, or bench- 
“ mark, for heights at Waterloo Bridge ; and have determined the difference of level 
“ between this point and the floor of the Council room, in the Apartments of the 
“ Society at Somerset House. 
“ The bench-mark, I have adopted, is the surface of the granite pedestal at the 
