"Is ours the only inhabited planet?" This book of 350 pages walks through numerous necessities for life to exist - AS every professional astronomer knows, there is a vast population of laymen for whom the really exciting problems of astronomy are not those associated with the finiteness or supposed expansion of space, or the sources of stellar energy, but with the canals on Mars and the possibility of life on Mars. The Astronomer Royal, Sir Harold Spencer, tells us of the findings of modern astronomy on these latter questions, and much besides, in a way that will not only interest the layman, but the professional scientist as well. It is a model of what such a book should be, popular and scientific at the same time, clear but concise in its writing, with the main theme standing out unburdened by irrelevant details, and the conclusions stated with balance and fairness. This book is a facsimile reproduction of the original printed text in shades of gray. Because this material is culturally important, we have made it available as part of our commitment to protect, preserve and promote knowledge in the world. This book has been formatted from their original version for publication. IMPORTANT, although we have attempted to maintain the integrity of the issues accurately, the present reproduction could have missing and blurred pages poor pictures due to the age of the original scanned copy. Because this material is culturally important, we have made it available as part of our commitment to protect, preserve and promote knowledge in the world. Visit our site are: https: //saucerianbooks.blogspot.com/