Barometric Observations. 77 
Jan, 22, 1822. 
Dear Sir,—Having sent the calculated results of the ob- 
servations on the Barometer in my last, up to November, and 
haying completed the year 1821, as to the monthly observations, 
I consider it due to yourself and correspondents to acknowledge 
the obligation J feel for the attention shown to the subject pro- 
posed by me; and to assure you that I shall feel great pleasure, 
at some future period, in renewing the course under some im- 
provements, and hope to be able to fix the zero by a permanent 
mark, in one or more convenient places in London ; whence, by 
means of a revised section of the Grand Junction Canal, extend the 
line of determined altitudes over a large district. The connexion 
of other canals, when their sections have been revised, will carry 
the line of known altitudes to nearly all the towns of importance 
in the country. The intermediate places may afterwards be deter- 
mined with considerable accuracy, by taking short distances and 
proper states of the atmosphere. 
It is highly to be regretted that the heights determined by 
the late Col. Mudge and others, in the great National Trigono- 
metrical Survey, cannot be depended on. I have been at the trou- 
bie of levelling, to determine the relative heights of several near 
the borders of the Grand Junction Canal, and am sorry to find 
a variation of 20, 30, and 40 feet from the heights published in 
the Survey. Considering the importance of some of the principal 
stations, particularly those used in ascertaining the relative length 
of degrees in the different sections of the English are, it would 
not be unworthy of the Honourable Board of Ordnance to correct 
these heights by actual levelling: the necessary time and expense 
would be very small. 
In your last Number are two months observations at Crump- 
sall and Manchester, and one at Pocklington, the calculated 
heights of which relative to Leighton | beg leave to send, in ad- 
dition to those of last month, viz. 
Crumpsall above Leighton. Manchester above Leighton. 
November 187 feet. November & feet. 
December 247 December 86. 
Pocklington above Leighton. 
December 11 feet. 
To Dr. Tilloch. Yours truly, 
B, BEvaANn. 
P.S. In Jast month’s letter I omitted to say Mr. Cary’s ba- 
rometer was Lelow Leighton, 
METEORO- 
