830 
deduced a complete list of elements as regards longi- 
tude ; and diminished the mean distance considerably. 
The true longitude by this calculation differed only 
13° from his previous estimation. He finds for the 
mean distance from the Sun 36 times that of our 
Earth (that of Uranus being 19), the period 217 
years, and the mass s345% of the Sun’s. Assuming 
the density of the planet to be the same as that of 
Uranus, he conjectures that the apparent diameter 
will be 3°°3; that it will therefore have a visible disk 
sufficient to distinguish it from a fixed star, and that 
its brilliancy should equal that of a star of the 8th 
or 9th magnitude. As the result of these supposi- 
tions, he found that the whole errors in the places 
of Uranus from 1781 to 1844 were reconciled within 
quantities amounting but in one instance to 5”; that 
the ancient observations of the 18th century were 
reconciled within 7” or 8”; and the oldest observa- 
tion of all, that of Flamsteed in 1690, had an out- 
standing error of 20”, a quantity very far from exces- 
PHYSICAL ASTRONOMY.—M. LEVERRIER—MR ADAMS. 
[Diss. VI. 
was anticipated and completed in France and Ger- 
many alone; England had nodirect participation. We 
mustnow, however, state briefly what occurred there of 
a similar character at the same time, and even earlier. 
Mr Joun Covcn Apams, when a student at St 
John’s College, Cambridge, in 1841, formed the de- 
sign of detecting the position of a perturbing planet 
which should account for the anomalous motions'of 
Uranus. He made a preliminary essay on the pro- 
blem in 1843, assuming the distance of the suspected 
body from the Sun to be double that of Uranus. 
I learn from good authority that he obtained a place 
for the unseen planet not very different from that 
which he finally adopted. Early in 1844 he ob- 
tained from Greenwich the valuable series of places 
of Uranus which were afterwards in like manner ap- 
plied for by M. Leverrier. In September 1845, he 
communicated to Professor Challis the elements of the 
new planet’s orbit (neglecting the inclination) and an 
ephemeris of its geocentric place; and in October he 
(139.) 
sive, considering the state of astronomy at that period. 
(137.) No one who read at the time the abstract of this 
resulting inyemarkable paper in the Comptes Rendus failed to 
the disco- be struck with it, not only as regarded the weighty 
transmitted the elements alsotothe Astronomer Royal. Mr Adams 
This, it will be observed, was soon after M. Leverrier’s preceded 
4 S ° : . Lever- 
attention was first directed to the subject, and nine vi30 5) 9 
vary of months previous to his announcement of the locality similar in- 
Neptune by matter, thus publicly announced, but also on account where the new body should be sought. Mr Adams vestiga- 
M. Galle. “ of the calm and well-grounded conviction which the afterwards repeated his calculation with a mean dis- "+ 
author manifested in the truth of his boldconclusions, tance zyth less than before, and considered himself 
and the definite manner in which he gives the chal- warranted, by the improvement thus produced on the 
lenge to practical astronomers to verify or disprove residual errors, in inferring that a farther consider- 
them. “ Since Copernicus declared” (according to the able diminution of the mean distance would satisfy 
prevalent tradition) ‘that when means should bedis- the observations still better. This was communicated 
covered for improving the vision, itwould be found that to Mr Airy on the 2d September 1846 ; subsequently 
Venus had phases like the moon, nothing,” writes Mr therefore to the publication of M. Leverrier’s Ele- 
‘Airy, “so bold, and so justifiably bold, has been uttered ments. Mr Adams, in communicating his results (at 
inastronomical prediction.” M.Leverrierhadhastened a later time) to the Astronomical Society, with charac- 
his calculations in anticipation of the approaching teristic modesty says, ‘I mention these dates merely 
opposition of the new planet in the autumn of 1846, to show that my results were arrived at independently, 
but it is very doubtful whether astronomers would and previously to the publication of M. Leverrier, 
have made the discovery at that time, but for his per- and not with the intention of interfering with his just 
sonal application to M. Galle, then assistant-astro- claims to the honors of the discovery, for there is no 
nomer at Berlin, where a powerful refractor suitable doubt that his researches were first published to the 
for the search existed. So ardent a conviction in a world and led to the actual discovery of the planet by 
manner compelled the proof which the geometer Dr Galle.” 
claimed, and M. Galle, whose intelligence and zeal = And such is no doubt the fact. The priorityof Mr (140.) 
are well known, pointed his telescope to the sky the Adams in the mathematical investigation is as certain = pee. 
very evening that M. Leverrier’s letter reached him. as that the researches of M. Leverrier alone produced discovered 
Fortunately provided with a newly published star the discovery of Neptune. Even the search for the in conse- 
map by Brenicker of that region of the heavens, which planet which took place in August and September 1°°"°° 
was not at that time diffused generally amongst 1846 at Cambridge by Professor Challis, was not oc- 
European observatories, he detected that same night casioned by Mr Adams’ researches only ; it was the 
(the 23d September 1846) a star-like body of the 8th near coincidence of the longitude assigned by Mr 
magnitude, not noted in the star chart, therefore a Adams in the previous October with that published 
wandering body, having a manifest disk from 23” to by M. Leverrier in June 1846 which induced Mr 
3” in diameter, and distant only jifty-four minutes of Airy to suggest this investigation of the heavens, 
a degree from the predicted place. and to offer (if need were) himself to bear the ex- 
(138.) It will be remarked that the discovery in question pense. Had the planet been discovered! at Cambridge 
1 The planet was indeed seen at Cambridge by Mr Challis, for it was recorded more than once amongst the numerous fixed 
stars whose places were taken down in the progress of the search; but as the comparisons of the “sweeps” were not made at 
the time, the discovery was anticipated by M. Galle, 
