the inconceivable. Siemens has made a very unsatisfactory effort to show that the force is conserved. He has made but few converts to his theory. It is the purpose of this monograph merely to expand the received idea of waste, by showing that the recipients of the prodigal bounty of the great giver of all good in our solar system—the sun—are far fewer than is usually supposed.
Before the spectroscope taught us that the reign of chemism is coextensive with that of physics, many conjectures were indulged in by astronomers as to the inhabitability of the planets in general. It was taken for granted that there was probably an endless variety in the forms, composition, and even original substance of matter. Vegetation and animalism probably assumed wonderful shapes, and were capable of existing amid conditions not only altogether different from the terrestrial, but altogether incompatible with life on this earth. This conception, unphilosophical a priori, and indirectly the fruit of the wonder-instinct and that bias inherited, according to Comte, from the theological régime, has been swept away, and the reign of law extended to the mystic dream-lands of the universe. No thinker so loosely hinged now as to imagine life without a certain degree of heat, light, and without oxygen, hydrogen, carbon, and all the chemical elements, and that too in protean forms. Nay, more, the forms and succession of life must be, wherever found, substantially such as we are familiar with. If Venus has human inhabitants, they are not one eyed Cyclops, nor does vegetation bury its leaves in the ground and spread its roots in the air. Organs, and functions, and instinct are there also, subject to the grand laws of selection and development. Further, the absence of conditions essential to the sustenance of life on our globe would be equally fatal in any other. This brings up the question in hand—the scarcity, as a part of the problem of the cost, of life.
What planets are inhabited? Let us begin with the giant worlds on the verge of the system. In the first place, as might have been conjectured even before the revelations of the spectroscope, from their great volume of light as compared with their distances from the sun, all of these great bodies are self-luminous. They are at least incandescent, and doubtless Jupiter and Saturn are in a fluid, perhaps gaseous state. There can not be the slightest doubt that they are no more fit for life than the sun itself. Will they ever become the habitations of living things? Ignoring their distance from the sun, which to an inhabitant of Saturn would have about the apparent magnitude that Jupiter has to us, there are other considerations which set that question at rest.
The volume of Jupiter, for example, is about 1,280, Saturn 991, Uranus 80, times that of the Earth. The density of Jupiter being about 1·40 and that of the Earth 5·48, it follows that the attraction exerted by Jupiter is, roughly, 300 times that of the Earth. A man
