2 NAGOTRE 
[May 4, 1899 
I cannot close the list of these preparatory studies 
without referring to a subject which interests the highest 
problems of astronomy of precision. 
The observations of the planets and of the moon 
depend on the coordinates of the fundamental stars, of 
which unfortunately we possess as yet no catalogue ab- 
solutely free from systematic errors. One of Newcomb’s 
constant preoccupations was to try to constitute a uni- 
form system of points of reference, at least in right 
ascension, this coordinate having we ghty importance in 
the case of observations of moving bodies. The cata- 
logues drawn up by him, and by Auwers, for the funda- 
mental and bright stars of the ecliptic, have shared in 
equal measure up to a very recent date the favour of 
astronomers. But the use, in the same scientific research, 
of elements derived from different sources, presents in- 
conveniences acknowledged for a long time. A reform 
in this direction had become very desirable. This cir- 
cumstance has again afforded Newcomb the opportunity 
of manifesting the inexhaustible resources of his activity 
and talent. An international conference, held in Paris 
in 1896, under the auspices of the Bureau des Longi- 
tudes, had as its object to elaborate a common system of 
constants and fundamental stars to be employed in the 
astronomical ephemerides. Newcomb took one of the 
most important parts in the discussions and resolutions 
of this conference. At its suggestion he has under- 
taken, not only the research of the definitive values to 
adopt for the lunar-solar precession and the planetary 
precession, but also the construction of a new catalogue 
of fundamental stars in accordance with the system of 
elements chosen by the Paris meeting of astronomers. 
Newcomb has consecrated these two later years to the 
accomplishing of this arduous task. The catalogue of 
fundamental stars, which he has just finished, will come 
into use in the beginning of Igor, and will realise in the 
work of astronomers that unity and simplification so long 
desired. 
I now come to the labours which have absorbed the 
greatest part of Newcomb’s scientific activity : they refer 
to the domain of celestial mechanics. 
At the time when the great work of Le Verrier had 
only reached the tables of Jupiter, Newcomb published 
an excellent theory of the two planets furthest from us, 
Uranus and Neptune. These tables, from the moment 
of their appearance, have been used by astronomers of 
every country. 
Among the greatest triumphs of Newcomb’s career 
must be counted his many and fruitful researches on the 
motion of the moon The theory of the moon bristles 
with difficulties. No one has yet succeeded in establish- 
ing a complete harmony between theory and observation. 
In his lunar tables, Hansen, in order to obtain this 
accordance for a limited interval of time, was obliged to 
attribute to an inequality arising from the action of 
Venus an empirical coefficient of an excessive amount, 
and to adopt besides an acceleration of the secular move- 
ment twice as great as that which results from the law of 
universal gravitation according to the calculations of 
two illustrious geometricians, Adams and Delaunay. 
Should we, as a great number of savan¢s think, attribute 
to Hansen’s number, so far from the theoretical value, 
an indisputable reality, and try to discover the physical 
NO. 1540, VOL. 60} 
causes of the anomaly ; or should we see the origin of 
the disagreement in an erroneous interpretation of his- 
torical documents? Newcomb did not recoil before the 
difficulties which the solution of this problem entailed. 
He discussed all the occultations observed since the 
invention of the telescope up to a recent time ; he him- 
self examined forgotten observations, buried for one. 
hundred and fifty years in the registers of the Paris 
Observatory. These neglected documents have thrown 
a vivid light on the question. In thus utilising an abun- 
dant harvest of new information, and correcting Hansen’s 
theory by the exclusion of every empirical coefficient, 
Newcomb arrived at results of fundamental importance. 
He proved, agreeing in this with Tisserand’s researches, 
that the eclipses of the Almagest, and those of the 
Arabs, as well as the ancient occultations, agree very 
well with the theoretical value of the secular acceleration ; 
and further, as a corollary, that the most ancient solar 
eclipses, the representation of which would seem to de- 
mand an increase of the secular acceleration, can without 
scruple be left out of consideration, either because the 
reality of the phenomenon remains doubtful, or because 
there exists too great an uncertainty in the hour and 
place of observation. 
One might withont inconvenience, therefore, adopt the 
theoretical acceleration of 6”, correcting the mean motion 
and the longitude of the epoch. But whatever value is 
chosen, and this was not anticipated, one must, after 
having suppressed Hansen’s erroneous inequality, resign 
oneself to introduce another notable empiric term of a- 
period of about two hundred and seventy years, and of 
an unexplained origin ; one simply notes that this ampli-. 
tude is nearly that of an inequality due to Venus, the 
existence of which is not doubtful. 
Besides this empiric inequality, Newcomb has dis- 
covered another, less. pronounced, with a coefficient 
superior to 1”, with an amplitude of about twenty-seven 
days, and appearing to be associated with a long period 
perturbation of the excentricity and perigee. These 
delicate deductions have since been confirmed by the 
theoretical researches of Messrs. Neison and Hill, which 
show that the terms in question are due to the action of 
Jupiter. By all these investigations, Newcomb has 
elucidated, in a masterly way, the actual state of the 
theory of the motion of our satellite. 
The two theories of the moon which must be con- 
sidered the best are those of the two celebrated 
geometricians, Delaunay and Hansen ; they are founded 
on totally different methods. By the help of a long, 
minute and tedious transformation, because it is a 
question of formule occupying several quarto volumes, 
Newcomb has rendered their expressions immediately 
comparable, bringing them moreover to a system of 
precise and uniform constants. 
Further, by this comparison, he has shown that, in 
spite of the difference of method, the two theories lead 
to identical results for solar perturbations, which form 
the essential part of them and are indeed the only ones 
which were calculated by Delaunay. 
I must now pass very briefly to some of Newcomb’s 
other memoirs. One of his most original researches is 
relative to Hyperion, Saturn’s seventh satellite, dis- 
covered almost simultaneously by Bond and Lassell. 
