[44]Proc. Amer. Acad., Vol. 1, p. 332.
[45]Observatory “Memoir on a Trans-Neptunian Planet.”
[46]Much of the following account is taken from “Searching Out Pluto” by Roger Lowell Putnam and Dr. V. M. Slipher in the Scientific Monthly for June, 1932, by whose courtesy it is used.
[47]515 asteroids and 700 variable stars were there disclosed.
[48]After X had been discovered two very weak images of it were found on photographic plates made in 1915—the year he published his Memoir.
[49]This figure slightly changed for later observations is on the opposite page.
[50]Dr. A. C. D. Crommelin, the highest authority in England on such matters, had expressed the same conclusion; and the Royal Astronomical Society had cabled its felicitations on the discovery. Professor Russell’s latest views may be found in infra.
[51]The non-expert reader must remember that the mass and the size—still more the apparent size—are very different things, and the mass is the only one that could be found by calculation, for this alone affects the attraction, which at such a distance is quite independent of the density and hence of the size. Moreover, the apparent size depends also upon the extent to which the surface reflects the light of the sun—technically termed the planet’s albedo—a matter that has no relation to the perturbation of another body.
[52]“The Astronomical Romance of Pluto”—Professor A. O. Leuschner—Publications of The Astronomical Society of the Pacific, August, 1932.
[53]See [page 181] supra.