Pluto.—Popular Astronomy for April contains Prof. V. M. Slipher's report on the Lowell Observatory, in which there are some more details about Pluto. It was not until Feb. 18, 1930, that Mr. Tombaugh discovered the images on plates taken on Jan. 23 and 29, and afterwards that on the plate of Jan. 21. It was examined visually with the 24-inch refractor. “No certain evidence of disk could be made out, although on. a few occasions its image seemed not quite like those of equally faint stars.” “Later tests . . . indicated that with Pluto's faintness his disk, if as much as 0.6″, could escape detection under good observing conditions.“ This would imply a diameter of 11,000 miles. It was found that Pluto was brighter visually than photographically, so a yellowish colour was inferred.