Simon Newcomb

“ Still, the difficulty and uncertainty attending all observations hitherto made upon the disk are such that no conclusion respecting the time of rotation can be regarded as established. Against the view of Schiaparelli is to be set the great improbability that a body so distant from the sun as Venus could be permanently so acted upon as to keep its axial rotation in precise coincidence with its orbital motion. Only one way seems to be open for settling the question; this is by spectroscopic observations of the displacement of the spectral lines at the two limbs of the planet. ”

“ As a matter of fact the actual motion of the planet during the century preceding, as derived from Leverrier's elements, was much nearer the truth than the elements themselves were. This arose from the fact that his very elliptic orbit, by its large eccentricity, brought the planet near to the sun, and therefore near to its true position, during the period from 1780 to 1845, when the action on Uranus was at its greatest. ”

“ A similar law holds true of the eccentricities and the perihelia. These may both be defined by the position of the centre of the orbit relative to the sun. If a be the mean distance and e the eccentricity of an orbit, the geometry of the ellipse shows that the centre of the orbit is situated at the distance ae from the sun, in the direction of the aphelion of the body. When the centres of the orbits are laid down on a diagram it is found that they are not scattered equally around the sun but around a point lying in the direction of the centre of the orbit of Jupiter. ”

“ Arago took the extreme ground that actual publication alone should be considered, rejecting Adams's communications to Airy and Challis as quite unworthy of consideration. He also suggested that the name of Leverrier should be given to the planet, but this proposal was received with so little favour outside of France that he speedily withdrew it, proposing that of Neptune instead. The observations at the first opposition showed that the planet was moving in a nearly circular orbit, and was at a mean distance from the sun much less than that set by Leverrier as the smallest possible. ”

“ Society. B. A. Gould, Report to the Smithsonian Institution on the History of the Discovery of Neptune, published by the Smithsonian Institution (Washington, 1850) , is the most complete and detailed history of all the circumstances connected with the discovery, and with the early investigations on the orbit of the planet, that has been published. Leverrier's investigation was published in extenso as an addition to the Connaissance des temps, and Adams's as an appendix to the Nautical Almanac for 1851. ”

“ A second memoir was presented by Leverrier in 1846 (June 1) . His investigation was more thorough than that of Adams. He first showed that the observations of Uranus could not be accounted for by the attraction of known bodies. Considering in succession various explanations, he found none admissible except that of a planet exterior to Uranus. Considering the distances to be double that of Uranus he then investigated the other elements of the orbit. He also attempted, but by a faulty method, to determine the limits within which the elements must be contained. ”

“ The best answer that can be made to this question is that, unless the smaller members of the group are almost perfectly black, a number great enough to produce any observable effect by their attraction would be visible as a faintly illuminated band in the sky. ”

“ But a simultaneous variation of all the elements would have shown that the representation of the observations of Uranus would be improved by a simultaneous diminution of both the eccentricity and the mean distance, the orbit becoming more nearly circular and the planet being brought nearer to the sun. ”

“ The position of A ls different in the case of different planetoids, but is generally about two-thirds of the way from S to J. The lines AC for different bodies are at any time scattered miscellaneously around the region A as a centre. AC may be called the constant of eccentricity of the planetoids, while SC represents its actual but varying eccentricity, Grouping of the Planetoids.—A curious feature of these bodies is that when they are classified according to their distances from the sun a tendency is seen to cluster into groups. ”

“ Since the mean distance and mean motion of each planet are connected by Kepler's third law, it follows that this grouping may also be described as a tendency toward certain times of revolution or certain values of the mean motion around the sun. ”

“ The computations of the probable mass of those known, based upon their probable diameter as concluded from the light which they reflect, have led to the result that their combined action must be very minute. ”

“ Such mean motions are nearly commensurable with that of Jupiter, and it is shown in celestial mechanics that when they exist the perturbations of the planet by Jupiter will be very large. It was therefore supposed that if the commensurability should be exact the orbit of the planet would be unstable. But it is now known that such is not the case, and that the only effect of even an exact commensurability would be a lib ration of long period in the mean motion of the planetoids. ”

“ Its apparent motion may be described as an oscillation from one side of the sun to the other, the complete period of which is 1.6 years, and the greatest elongation about 45° on each side of the sun. When east of the latter it appears as the “evening star” in the west after sunset, while near western elongation it is seen as the “morning star” before sunrise. ”

“ Belopolski’s measures were decidedly in favour of an axial rotation, while the Lowell results were not.
Other observations than those we have cited show that Venus is surrounded by an atmosphere so filled with clouds that it is doubtful whether any view of the solid body of the planet can ever be obtained. The first evidence in favour of an atmosphere was found in the factAtmosphere of Venus. ”

“ In the telescope it presents much the appearance of burnished silver, without spot or blemish. It is true that observers have from time to time thought they could detect slight variations of shade indicating an axial rotation. ”

“ Comparing the stars on the chart one by one with the heavens it was found that an eighth magnitude star now visible was not on the chart. This object was observed until after midnight, but no certain motion was detected. ”