ARE THE PLANETS HABITABLE?

Astronomical Society of the Pacific.i6 5 having two distinct foci separated by about half an inch, and, if bright enough, can be distinguished from ordinary stars merely by the aspect of the image.The visibility of planetary details differing greatly in color from the general surface tint, would doubtless be much affected by the same peculiarity of large telescopes.Thus, a fine blue line on the surface of Jupiter would be spread out into a diffuse band of considerable width at the visual focus, and, if faint, would certainly escape detection.Such differences of focus have been noticed in making drawings of Mars during the opposition of 1890.This is a subject of importance, and one which has as yet received little attention.