ACCORDING to Science Service, of Washington, D.C., it is now definite that the two hundred-inch telescope will be erected on Palomar Mountain, 45 miles north-east of San Diego, California. Astronomers have never felt completely satisfied with the ‘seeing’ at Mount Wilson. Bad ‘seeing’ arises from local irregularities in the atmospheric refraction which have the effect of distorting the stellar image, especially when a very large aperture telescope is being used; and since it was supposed that convection currents of air running up the steep sides of Mount Wilson contributed materially to the imperfections in the seeing at that observatory, a search for better seeing has been conducted on many plateaux and flat-topped peaks in southern Cali fornia. The tests of seeing were made by observing Pt laris through a standard telescope and noting the character of the image from night to night. The flat-topped Palomar has excellent seeing qualities; it is further advantageous in that it is remote from any great city. Scattered light from Los Angeles and its environs finds its way into the 100-inch reflector on Mount Wilson, and imposes a limit on the length of exposure which one can give to a photographic plate. It may be added that the 200-inch mirror is to be cast at Corning, N.Y., the scene of a previous 200-inch cast, now kept as a ‘spare’, while the mirror will be ground and the telescope itself constructed in Pasadena, at the California Institute of Technology. This institution will be responsible for the administration of the telescope when completed.