left in such a state that it would be a
comparatively simple task for a future astronomer to correct and
complete it, yet it was not permitted to the original author of it to
do this. To avoid the necessity of frequent reference to this work in
the history of Airy's remaining years, it will be convenient to
summarize it here. It was commenced in 1872: "On Feb. 23rd in this
year I first (privately) formed the notion of preparing a Numerical
Lunar Theory by substituting Delaunay's numbers in the proper
Equations and seeing what would come of it." From this time forward
till his power to continue it absolutely failed, he pursued the
subject with his usual tenacity of purpose. During his tenure of
office every available opportunity was seized for making progress with
his Lunar Theory, and in every Report to the Visitors a careful
statement was inserted of the state in which it then stood. And, after
his resignation of office, it formed the bulk of his occupation. In
1873 the Theory was formed, and by 1874 it was so far advanced that he
published in the Monthly Notices of the Royal Astronomical Society a
statement of the fundamental points of the Theory. In 1875, the
Theory having advanced to a stage where extensive arithmetical
computation was required, he obtained a small grant from the
Government in aid of the expense of the work, and other grants were
made in subsequent years. By 1878 the calculations were so far
advanced that an opinion could be formed as to the probable accuracy
of the Theory, and the following remark is made: "A cursory collation
of the terms relating to the Areas (in the Ecliptic) led me to suppose
that there might be some error in the computations of the Annual
Equation and related terms;" but no error could be discovered and the
work proceeded. The complex character of the Theory, and the extreme
care required in the mathematical processes, are well illustrated by
the following statement, which occurs in the Report of 1879, "An
important error in the theoretical formulae for Variations of Radius
Vector, Longitude, and Latitude, was discovered; some calculations
depending on them are cancelled." In 1880 and 1881 the work was
continued, but was "sadly interrupted by the pressure of the Transit
of Venus work and other business." After his resignation of the Office
of Astronomer Royal he had no further public assistance, and did much
of the computations himself, but a sum of _L100_ was contributed by