NALURE 
565 
THURSDAY, OCTOBER 14, 1886 
SCIENTIFIC WORTHIES 
XXIV.—JOHN CoucH ADAMS 
| DINOS ONS J. C. ADAMS, whose portrait we this 
day present to our readers, entered St. John’s Col- 
lege, Cambridge, in 1839. He soon gave promise of 
those great mathematical powers that have brought such 
renown to his University. He came out as Senior 
Wrangler in 1843, and the excellence of his answering 
is still a tradition at Cambridge. 
By what seems to have been an inspiration of genius, 
he was guided after taking his degree to concentrate his 
talents on the solution of an astronomical problem of 
excessive interest but of corresponding difficulty. The 
planet Uranus had shown irregularities in its motion. 
The orbit differed from the elliptic path which an undis- 
turbed planet would pursue, and the deviations could not 
be fully accounted for by the influences of the other 
known planets. The only explanation of the discrepancy 
which astronomers could be expected to favour lay in the 
supposition that there was some other still more remote 
planet yet unknown. 
It was the search for this unknown planet which 
attracted the distinguished Senior Wrangler. We can 
imagine the delight with which a well-equipped mathe- 
matician would throw himself into the solution of such a 
problem. On it he was to concentrate the powers that 
had been cultivated during his University career. 
The planet was to be sought for by the measured devia- 
tions of Uranus from its calculated positions. ‘Those who 
have ever had occasion to study the planetary theory are 
well aware of the difficulty and the laborious intricacy of 
the subject. To most of us it has seemed-a thorny and 
difficult problem when the planet is given to find the per- 
turbations. What are we to say of the difficulty of the 
converse problem, Given the perturbations and find the 
planet! This was the problem which Adams faced, and 
which, to his imperishable fame, he succeeded in solving. 
The story of this discovery is familiar to all, and the con- 
troversies that arose have long since diedaway. To each 
of the joint discoverers, Leverrier and Adams, the gold 
medal of the Royal Astronomical Society was presented on 
February 11, 1848. In his address on the occasion, Sir 
John Herschel, speaking of the two astronomers, says :— 
“MM. Leverrier and Mr. Adams—names which as genius 
and destiny have joined them, I shall by no means put 
asunder ; nor will they ever be pronounced apart so long 
as language shall celebrate the triumphs of Science in her 
sublimest walks. On the great discovery of Neptune, 
which may be said to have surpassed, by intelligible and 
legitimate means, the wildest pretensions of clairvoyance, 
it would now be quite superfluous for me to dilate. That 
glorious event and the steps which led to it, and the 
various lights in which it has been placed, are already 
familiar to every one having the least tincture of science, 
. . - I will only add that as there is not nor henceforth 
ever can be the slightest rivalry on the subject between 
these two illustrious men—as they have met as brothers, 
and as such will, I trust, ever regard each other—we have 
made, we could make, no distinction between them on this 
occasion. May they both long adorn and augment our 
science, and add to their own fame, already so high and so 
pure, by fresh achievements.” 
VOL. XXXIV.—No. 885 
The discovery of Neptune was a brilliant inauguration 
of the astronomical career of Adams. We cannot here 
enter into a detailed account of his numerous labours. 
There is an admirable account given of them up to the 
year 1866 in the address of Mr. De la Rue to the Royal 
Astronomical Society, when Adams was again the re- 
cipient of a gold medal. We find that he has worked at 
and written upon the theory of the motions of Biela’s 
comet ; he made important corrections to the theory of 
Saturn ; he made an elaborate investigation of the mass 
of Uranus, to which he was naturally attracted from its 
importance in the theory of Neptune ; he has improved 
the methods of computing the orbits of double stars: but 
next to the discovery of Neptune the fame of Adams 
mainly rests on his researches on the moon and on the 
theory of the November meteors. To each of these sub- 
jects we must devote some attention. 
In the Pfz?. Trans., vol. cxliii. part iii. p. 397, his paper 
was published “on the secular variation of the moon’s 
mean motion.” This memoir originated a long contro- 
versy, in which the ablest mathematicians have par- 
ticipated. 
The “ secular acceleration of the moon’s mean motion ” 
is the phrase which denotes a gradual but excessively 
slow diminution in the moon’s periodic time. Although 
the amount of this diminution is very minute, yet the fact 
that it always tended in the same direction rendered the 
amount accumulative, so as to become very perceptible 
im the succession of ages. The explanation of the acce- 
leration formed a problem on which the great mathe- 
maticians at the close of the last century exercised their 
powers, and at length the explanation was given by 
Laplace. He found that, when the analytical expression 
for the moon’s mean motion was developed, it contained 
certain terms depending upon the eccentricity of the 
earth’s orbit. This eccentricity varies in consequence of 
the planetary perturbations, and hence the changes of the 
moon’s mean motion. Laplace calculated the amount, 
and deduced, or thought he had deduced, a correspond- 
ence between the observed value and the calculated 
value. The high authority of Laplace, and the brilliant 
success of his efforts to explain other perturbations in our 
system, led to an acquiescence in his results, and the 
great problem of the secular acceleration was believed to 
have been solved. 
In Mr. Adams’s paper he joined issue with Laplace. 
The question was fortunately one which did not involve 
any real element of uncertainty. It was a problem in 
mathematics, or rather dynamics—difficult no doubt, but 
not really open to any ambiguity. Prof. Adams showed 
that Laplace had only considered a part of the disturbing 
influence, and when the true amount was determined, 
it came out to be only about one-half that found 
by Laplace. So serious a charge received the careful 
consideration which it merited. Several leading mathe- 
maticians impugned the calculations of Adams, but 
he was able to vindicate his theory at every point, and 
finally the correctness of his calculations was verified in 
one manner by M. Delaunay, and in another by Prof. 
Cayley. The importance of this result is not to be esti- 
niated merely by its value as a correction to Laplace. 
The author of the ‘‘ Mécanique Céleste,” like other 
writers, makes errors in his work. Numerous errors have 
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