"Cambridge Observatory, Oct. 15.
"The allusion made by Sir John Herschel, in his letter contained in the _Athenaeum_ of October 3, to the theoretical researches of Mr. Adams, respecting the newly-discovered planet, has induced me to request that you would make the following communication public. It is right that I should first say that I have Mr. Adams's permission to make the statements that follow, so far as they relate to his labors. I do not propose to enter into a detail of the steps by which Mr. Adams was led, by his spontaneous and independent researches, to a conclusion that a planet must exist more distant than Uranus. The matter is of too great historical moment not to receive a more formal record than it would be proper to give here. My immediate object is to show, while the attention of the scientific public is more particularly directed to the subject, that, with respect to this remarkable discovery, English astronomers may lay claim to some merit.
"Mr. Adams formed the resolution of trying, by calculation, to account for the anomalies in the motion of Uranus on the hypothesis of a more distant planet, when he was an undergraduate in this university, and when his exertions for the academical distinction, which he obtained in January 1843, left him no time for pursuing the research. In the course of that year, he arrived at an approximation to the position of the supposed planet; which, however, he did not consider to be worthy of confidence, on account of his not {388} having employed a sufficient number of observations of Uranus. Accordingly, he requested my intervention to obtain for him the early Greenwich observations, then in course of reduction;--which the Astronomer Royal immediately supplied, in the kindest possible manner. This was in February, 1844. In September, 1845, Mr. Adams communicated to me values which he had obtained for the heliocentric longitude, excentricity of orbit, longitude of perihelion, and mass, of an assumed exterior planet,--deduced entirely from unaccounted-for perturbations of Uranus. The same results, somewhat corrected, he communicated, in October, to the Astronomer Royal. M. Le Verrier, in an investigation which was published in June of 1846, assigned very nearly the same heliocentric longitude for the probable position of the planet as Mr. Adams had arrived at, but gave no results respecting its mass and the form of its orbit. The coincidence as to position from two entirely independent investigations naturally inspired confidence; and the Astronomer Royal shortly after suggested the employing of the Northumberland telescope of this observatory in a systematic search after the hypothetical planet; recommending, at the same time, a definite plan of operations. I undertook to make the search,--and commenced observing on July 29. The observations were directed, in the first instance, to the part of the heavens which theory had pointed out as the most probable place of the planet; in selecting which I was guided by a paper drawn up for me by Mr. Adams. Not having hour xxi. of the Berlin star-maps--of the publication of which I was not aware--I had to proceed on the principle of comparison of observations made at intervals. On July 30, I went over a zone 9' broad, in such a manner as to include all stars to the eleventh magnitude. On August 4, I took a broader zone and recorded a place of the planet. My next observations were on August 12; when I met with a star of the eighth magnitude in the zone which I had gone over on July 30,--and which did not then {389} contain this star. Of course, this was the planet;--the place of which was, thus, recorded a second time in four days of observing. A comparison of the observations of July 30 and August 12 would, according to the principle of search which I employed, have shown me the planet. I did not make the comparison till after the detection of it at Berlin--partly because I had an impression that a much more extensive search was required to give any probability of discovery--and partly from the press of other occupation. The planet, however, was _secured_, and two positions of it recorded six weeks earlier here than in any other observatory,--and in a systematic search expressly undertaken for that purpose. I give now the positions of the planet on August 4 and August 12.
Greenwich mean time.
Aug. 4, 13h. 36m. 25s. {R.A. 21h. 58m. 14.70s. {N.P.D. 102 deg. 57' 32.2"
Aug. 12, 13h. 3m. 26s. {R.A. 21h. 57m. 26.13s. {N.P.D. 103 deg. 2' 0.2"
"From these places compared with recent observations Mr. Adams has obtained the following results:
Distance of the planet from the sun 30.05 Inclination of the orbit 1 deg. 45' Longitude of the descending node 309 deg. 43' Heliocentric longitude, Aug. 4 326 deg. 39'
"The present distance from the sun is, therefore, thirty times the earth's mean distance;--which is somewhat less than the theory had indicated. The other elements of the orbit cannot be approximated to till the observations shall have been continued for a longer period.
"The part taken by Mr. Adams in the theoretical search after this planet will, perhaps, be considered to justify the suggesting of a name. With his consent, I mention _Oceanus_ as one which may possibly receive the votes of astronomers.--I {390} have authority to state that Mr. Adams's investigations will in a short time, be published in detail.
"J. CHALLIS."[803]
