When Neptune was _visually_ discovered by Galle, at Berlin, he was assisted in his observation by Prof. d'Arrest. The incident is thus described by Dr. Dreyer, "On the night of June 14, 1874, while observing Coggia's comet together, I reminded Prof. d'Arrest how he had once said in the course of a lecture, that he had been present at the finding of Neptune, and that 'he might say it would not have been found without him.' He then told me (and I wrote it down the next day), how he had suggested the use of Bremiker's map (as first mentioned by Dr. Galle in 1877) and continued, 'We then went back to the dome, where there was a kind of desk, at which I placed myself with the map, while Galle, looking through the refractor, described the configurations of the stars he saw. I followed them on the map one by one, until he said: "And then there is a star of the 8th magnitude, in such and such a position," whereupon I immediately exclaimed: "That star is not on the map."'"[179] This was the planet. But it seems to the present writer that if Galle or d'Arrest had access to Harding's Atlas (as they probably had) they might easily have found the planet with a good binocular field-glass. As a matter of fact Neptune is shown in Harding's Atlas (1822) as a star of the 8th magnitude, having been mistaken for a star by Lalande on May 8 and 10, 1795; and the present writer has found Harding's 8th magnitude stars quite easy objects with a binocular field-glass having object-glasses of two inches diameter, and a power of about six diameters. SUPPOSED PLANET BEYOND NEPTUNE.--The possible existence of a planet beyond Neptune has been frequently suggested. From considerations on the aphelia of certain comets, Prof. Forbes in 1880 computed the probable position of such a body. He thought this hypothetical planet would be considerably larger than Jupiter, and probably revolve round the sun at a distance of about 100 times the earth's mean distance from the sun. The place indicated was between R.A. 11{h} 24{m} and 12{h} 12{m}, and declination 0° 0' to 6° 0' north. With a view to its discovery, the late Dr. Roberts took a series of eighteen photographs covering the region indicated. The result of an examination of these photographs showed, Dr. Roberts says, that "no planet of greater brightness than a star of the 15th magnitude exists on the sky area herein indicated." Prof. W. H. Pickering has recently revived the question, and has arrived at the following results: Mean distance of the planet from the sun, 51·9 (earth's mean distance = 1); period of revolution, 373½ years; mass about twice the earth's mass; probable position for 1909 about R.A. 7{h} 47{m}, north declination 21°, or about 5° south-east of the star κ Geminorum. The supposed planet would be faint, its brightness being from 11½ to 13½, according to the "albedo" (or reflecting power) it may have.[180]