436 REPORT—1840. 
nomical Institution have afforded every facility for its erection, 
and have removed their camera-obscura for that purpose. 
Mr. Osler has furnished the instrument below prime-cost, 
but I regret to say, that the unavoidable expenditure for put- 
ting the instrument in working order, carriage, and placing 
it in its present position, amounts to 31/.; so that the sum 
of 60/., granted by the Association, has been exceeded by 
112. I have, however, the satisfaction of stating, that the 
Anemometer is now in complete work, under the superintend- 
ence of Prof. Henderson and Mr. Wallace, of the Edinburgh 
Observatory. J. D. Forses. 
Glasgow, September 23, 1840. 
On the part of a Committee appointed for the purpose of caus- 
ing a plate to he engraved for printing paper ruled in squares, 
Prof. Forbes reported,— 
That the plate was engraved, and that the paper, 22 inches 
by 26, and ruled in squares of one tenth of an inch, each tenth 
line being stronger than the others, was ready for the service 
of the members of the Association, at cost price, on application 
to Messrs. Johnston, Engravers, Edinburgh. 
Report on the Application of a Portion of the Sum of Fifty 
Pounds, voted by the British Association at its Meeting at 
Birmingham, in 1839, for Discussion of Tide Observations. 
By the Rev. W. WHEWELL. 
(With a Plate.) 
A portion of this sum has been expended upon calculations, 
having for their object to determine the effect of the moon’s de- 
clination upon the tides. The determination of this correction 
is attended with peculiar difficulties, and has hitherto been incom- 
pletely effected. Thesedifficulties arise from this: that the moon’s 
mean declination is different in different years, through a cycle 
of eighteen years, the period of revolution of her nodes. The 
inclination of her orbit to the equator varies from about 18° 20’, 
its amount in 1829 and 1830, to 28° 40’, its amount in 1837 
and 1838. Hence, if we attempt to determine the declination 
correction (of height, for instance) by taking the difference of 
the height from the mean height (allowance being made for 
other corrections), we refer to a variable standard. Accordingly, 
if we find from the observations the mean semimenstrual ine- 
quality for the successive years, it will be different in conse- 
quence of the different mean declinations in successive years ; 
and it is only by taking a series of nine or more years that we 
