146 
WOODWARD. 
difficult of all the problems he had to attack, mid the one 
to which he devoted the greater part of his life, is the capital 
gravitational problem presented in the motion of the moon. 
.Vs has been indicated already, this motion had baffled the 
ingenuity of his most eminent predecessors and contempo- 
raries, and, as shown in his most recent contributions to the 
subject, this motion is not yet fully harmonized with the 
Newtonian law. It should be said at once, however, that 
he made great progress in the treatment of this grand prob- 
lem, and his tenacity of purpose as an investigator is well 
attested by the fact that his last as well as his first more 
important memoir is devoted to this uniquely difficult sub- 
ject of research. 
The first memoir, to which reference has just been made, 
was published in 1875, and is so important a contribution 
that it must serve as a test for all previous investigations 
as well as a foundation for all future researches in the sub- 
ject. During the ensuing forty years Professor Newcomb 
published many minor papers and memoirs bearing on this 
subject, terminating with a summary which appeared in the 
monthly notices of the Royal Astronomical Society in 1894. 
Soon after he became a Research Associate of the Carnegie 
Institution of Washington, in 1902, he renewed his attacks 
on the subject and issued, in 1907, an additional memoir on 
the inequalities in the motion of the moon produced by the 
action of the planets.* 
More recently he recurred to his earlier memoir and took 
up again a discussion of the mean motion and other elements 
of the moon as derived from eclipses and occupations from 
the period of the earliest Babylonian records to the present 
time. This was his last great work in this field, and it was 
his good fortune to announce its substantial completion on 
the occasion of my last conference with him, in the latter 
part of May of this year, when he tvas fully aware of the 
approaching termination of his activities. This memoir, T 
understand, is to be published, as are all of his principal 
papers with reference to the solar system , under the auspices 
♦Publication No. 72 of the Carnegie Institution of Washington. 
