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plicable to the theory of the mutual perturbations of Uranus and Neptune. The successive periods of conjunction and opposition, occurring at intervals of eighty-four years, that is, in about the time of revolution of Uranus, this planet is always at the same part of its orbit when it is most affected by the action of Neptune. The action of Neptune, consequently, assumes a fixed, permanent, undisturbed character, so that it can hardly be recognized as perturbation by the practical observer. It is far otherwise with the ordinary class of perturbations, where the place of greatest disturbance varies from point to point of the orbit; thus the place of greatest disturbance in the case of the theoretical planet would not have remained stationary, but have varied 80° upon the orbit of Uranus at each successive conjunction and opposition ; so that the disturbance could not in this case be disguised to any great extent under the fixed laws of ordinary elliptic motion. In the case of Neptune, its action on Uranus is to be detected in the comparatively small differences between its character and that of an elliptic motion, and the difference between the influence at opposition and that at conjunction. In undertaking, therefore, anew the solution of the problem of the perturbations of Uranus, with the assumption of the actual period of Neptune, instead of that adopted in the former theories, I found at once that I could not profit by the previous researches of Adams and Leverrier. The problem now presented, instead of being of the usual character, assumed a differential form by the disguise of the primary perturbations under the aspect of elliptic motions, and the whole ques. tion now rested upon the secondary perturbations, which were comparatively unimportant in the previous theories.'

“There is a popular notion, which hardly deserves to be refuted before a scientific body, that the less distance of Neptune than the planet of geometry is compensated by its smaller mass, so that its action upon Uranus is the same with that which was predicted. But the fallacy of this view of the subject, which takes no cognizance of the chief difficulty of the problem arising from the unknown orbit of Uranus, is obvious enough from a simple inspection of the following table, in which no one can fail to perceive the difference between the actions of the two planets. The second column of this table, which comprises the action of the theoretical planet of Adams's second hypothesis, is copied from page 27 of Adams's memoir.

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+ 150

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1845,
3421 1797, + 163

– 1816
1840,
- 118

3377 1792, # 181 1967 1835, - 96 3235 1787,

+178

2210 1829 2964 1782,

2504 1824, - 44

2684
1769,

3225 1819, - 13 2393

1756,

- 3431 1813, + 35 - 2072 1715,

- 1845 1808, + 83 - 1881

- 2947 1803,

- 1781 “ The difference in the action of the two planets is just balanced by the difference in the corrections of the elements of Uranus in the two theories. The corrections are given in the following table.

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1690,

Corrections in the Elements of the Orbit of Uranus of the
Mean Annu- Mean Longitude of

a Longitude of al Motion Distance. Epoch,

From the Theory of

Mean

Longitude of Eccentricity.

Perihelion.

Adams's second hypo

thetical planet, : -0.17846 +0.000148 – 4762 +0.0001954 + 1010.5 Neptune with Peirce's

computed mass, . : -1.13560 +0.000942 +2575.4 – 0.0003626 + 8252.4 Neptune with Struve's

mass, .....1-0.10387 +0.000086 +3511.7 -0.00055101 +11171.3

Mr. Bond communicated an account of his recent observations on the great nebula surrounding of Orionis ; with drawings illustrating its appearance as seen through the Cambridge refractor. Of the resolution of parts of the nebula Mr. Bond expresses himself with confidence. Several new stars are added in the vicinity of the Trapezium, and the connection of the nebulous districts about C and · Orionis with the great nebula conclusively established.

The paper was referred for publication in the Memoirs, as was also a communication from Mr. G. P. Bond, on “Some Methods of Computing the Ratio of the Distances of a Comet from the Earth.”

Professor Agassiz made some remarks on the distinctive characters of the family of Cyprinoids or suckers, as distinguished from the Cyprinodons, and illustrated the remarkable difference between the sexes, which had caused the establishment of a large number of nominal species.

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