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XI. On the Diurnal and Annual Inequalities of Terrestrial Magnetism, as deduced 
from Observations made at the Royal Observatory, Greenwich, from 1858 to 1863; 
being a continuation of a communication on the Diurnal Inequalities from 1841 to 
1857 , printed in the Philosophical Transactions, 1863. With a Note on the Luno- 
diurnal and other Lunar Inequalities, as deduced from observations extending from 
1848 to 1863. By George Biddell Aiet, Astronomer Royal. 
Received July 27 , — Read December 10, 1868. 
The paper which I have the honour now to submit to the Royal Society is similar, in 
its general character, to that which was printed by the Society in the Philosophical 
Transactions for 1863, as containing in a contracted form the results of very extensive 
observations which have been printed, and of detailed calculations founded on them 
which are prepared for printing, in the legitimate organ of publication of the observa- 
tions made in the Royal Observatory. For the principal part of the work, the results 
are here exhibited to the eye in the shape of diagrams. 
The instruments employed are precisely the same which were used in the second part 
of the former investigation, from 1848 to 1857, mounted in the same place, and treated 
in the same manner ; and the observations are reduced by application of the same for- 
mulae. The only difference in the form of exhibition is, that Greenwich Mean Time is 
here exclusively adopted instead of Gottingen Mean Time, which was used in the former 
paper. It will be remembered that the longitude of Gottingen is 0 h 39 m 46 s- 5 East of 
Greenwich. The nominal time, therefore, of the occurrence of a phenomenon is less in 
the results now presented than in those of the former paper ; or, the position on the 
curves of the figures 1, 2, 3, &c. for hours of time is more advanced than in the former 
paper, by 40 m nearly. 
TREATMENT OF THE PHOTOGRAPHIC CURVES. 
The first operation, in the treatment of the photographic records of the magnetometers, 
was to withdraw the sheets for those days on which the disturbances were so great as to 
make it difficult to draw a curve-line representing the mean path of the photographic 
spot. The actual list of days will be given in the detailed Greenwich publication ; but 
it may be interesting here to state the number of days thus omitted, including the back 
series from 1841 to 1857. 
1841 . . 9 
1842 . . 10 
1843 . . 7 
1844 . . 5 
1845 . . 5 
1846 . . 17 
1847 . . 20 
1848 . . 20 
1849 . . 2 
1850 . . 6 
1851 . . 13 
1852 . . 17 
1853 . . 18 
1854 . . 13 
1855 . . 4 
1856 . . 0 
1857 . . 10 
1858 . . 6 
1859 . . 15 
1860 . . 14 
3 
5 
1861 . . 
1862 . . 
1863 . . 
o 
