434 REPORT— 1840. 
group including the United States promises to be the most promi- 
nent. 
Only a very trifling sum (under two pounds) has been hitherto 
expended (for the printing, by Messrs. Stewart and Murray, of 
the skeleton forms) out of the original grant of 100/.; but the 
continuance of the grant will be required to meet the further re- 
quisite expenses. 
It is only justice to Mr. Birt to observe, that his part of the 
work appears to be executed with great care and judgment. 
(Signed) J. F. W. Herscue.. 
Mr. Birt’s Letter, alluded to in the above Report. 
Metropolitan L. and S. Institution, September 3, 1840. 
Dear S1r,—I herewith inclose the four sheets of curves mentioned in my 
last, also the tables of reduced barometric readings from which they are pro- 
jected. The curves of England and Ireland generally differ, in some cases con- 
siderably, with the exception of those observed in December 18386, on which oc- 
casion the similiarity between the Markree, Oxford, London, and Ashurst 
curves especially, as their apices occur about the same hour, is interesting. 
The occurrence of the apices of the Edinburgh, Halifax, and Oxford curves at 
later periods, and in the order here mentioned, appears to indicate a progres- 
sion of the barometric undulation from the north or north-east; and some of 
the remaining sheets alse indicate a progressive movement. 
I have not yet proceeded either to rounding off the curves, or to reading off 
the altitudes on the hour-lines. In the first instance, the undulations only 
which form the hourly observations assume a rising and falling in straight 
lines, will probably require a gentle rounding, so that the summit should pass 
through the point; for I see clearly, as you observed, that the points must not 
be interfered with, on account of the similar flexures in different curves. Do 
you consider any advantage would be gained from combining curves that are 
evidently similar, so that means of those similar curves may be obtained from 
similar altitudes above or below the mean-line, by bringing the apices and flex- 
ures on the same vertical ordinates, allowing for difference of longitude? 
The general dissimilarity of the curves obtained in Great Britain and Ireland, 
has suggested this to me also, that in future observations of the kind, it would 
be desirable to have the stations augmented, and, if possible, the observation 
of a complete elevation and depression at each. 
I hope you will receive the present sheets in good time for the meeting, 
And remain, dear Sir, 
Yours very respectfully, 
W. R. Birt. 
P.S.—In the Halifax curve of September, there are probably two errors. I 
have accordingly left the curve incomplete. 
The scale I have used is 1°5 of the larger divisions, equal -1 of an inch. 
Sir John F. W. Herschel. 
On the Temperature and Conducting Power of different Strata. 
By Professor Forbes. 
In this report, Professor Forbes gave the results of the ob- 
servations made at Edinburgh during the year 1839, upon 
