[Footnote B: Light Science for Leisure Hours, Proctor, pp. 42-52.] [Footnote C: The Problems of Astronomy, S. Newcomb, Science, May 21, 1897.] [Sidenote: The solar system is only one of many.] Sir Robert Ball expresses his views as follows: "The group to which our sun belongs is a limited one. This must be so, even though the group included all the stars in the milky way. This unnumbered host is still only a cluster, occupying, comparatively speaking, an expressibly small extent in the ocean of infinite space. The imagination will carry us further still--it will show us that our star cluster may be but a unit in a cluster of an order still higher, so that a yet higher possibility of movement is suggested for our astonishment."[A] [Footnote A: The Story of the Sun, R. S. Ball, pp. 360, 361.] Another eminent astronomer expresses the same idea briefly but eloquently: "It is true that from the highest point of view the sun is only one of a multitude--a single star among millions--thousands of which, most likely, exceed him in brightness, magnitude and power. He is only a private in the host of heaven."[A] [Footnote A: The Sun, C. A. Young, p. 11.] And still another student of the stars propounds the following questions: "Does there exist a central sun of the universe? Do the worlds of Infinitude gravitate as a hierarchy round a divine focus? Some day the astronomers of the planets which gravitate in the light of Hercules (towards which constellation the solar system is moving) will see a little star appear in their sky. This will be our sun, carrying us along in its rays; perhaps at this very moment we are visible dust of a sidereal hurricane, in a milky way, the transformer of our destinies. We are mere playthings in the immensity of Infinitude."[A] [Footnote A: Popular Astronomy, C. Flammarion, p. 309.] [Sidenote: Scientists believe that heavenly bodies are inhabited by living, thinking beings.] It is not strange that men who have learned to look at the universe in this lofty manner should go a step farther, beyond the actually known, and suggest that some of these countless heavenly bodies must be inhabited by living, thinking beings. Sober, thoughtful truthseekers, who never advance needlessly a new theory, have suggested, in all seriousness, that other worlds than ours are peopled. For instance, "What sort of life, spiritual and intellectual, exists in distant worlds? We can not for a moment suppose that our little planet is the only one throughout the whole universe on which may be found the fruits of civilization, warm firesides, friendship, the desire to penetrate the mysteries of creation."[A] [Footnote A: The Problems of Astronomy, S. Newcomb.] Such, then, is in very general terms the view of modern astronomy with reference to the constitution of the universe. Most of the information upon which this view rests has been gathered during the last fifty years.