Page:Popular Science Monthly Volume 67.djvu/246

240 from what they are to-day. This is astronomical work of importance awaiting research.

We desire to know much more concerning the individual planets. Even-body asks, 'Are the planets inhabited?' and no favorable answer has yet been given. If one means by the question, inhabited by such beings as we are structurally, then one can say that if one of us were transported to any of the planets we could not live there a minute. Some, like Jupiter, are too hot; others, like the moon, too cold, or without air to breathe or water to drink, or with too great or too little gravity for our bodies. One does not need to assume such likeness, especially since we know something of the past history of man and animals on the earth, adapted to it in form, size, structure, habits and intelligence all correlated. To assume intelligence of our type is hardly allowable any more than for structures like ours. Vertebrate skeletons are not necessarily the only form in which intelligence of high type may abide. The implements and skill of the astronomers are yet to determine what can be learned about this question. Taking what we know about the development of life on earth, it would seem to be insanely improbable that among the millions of millions of huge bodies in the universe, all apparently made of the same kinds of matter and subject to the same laws, that the earth is the only one among them all to have life and mind developed upon it. But at present we do not know that it may not be true. Let the twentieth century find out.

Geology: The whole of geology was a gift of the nineteenth century. There was nothing that deserved the name before it, yet more than half of the land of the globe has not yet been surveyed, and many geologic problems are yet unsettled, concerning regions that have been studied. The mineralogical relations and precedents among basalts, granites and other rocks, as well as the physical conditions that determined composition, arrangement and distribution, remain to be determined. Volcanic phenomena are not at all well understood. The composition of the interior of the earth is quite unknown; its temperature, and the rate of heat conductivity of the various rocks—questions which, when answered, will have much to say about the age of the earth and especially of the length of time since it has been a habitable body for any living things. At present there are two camps interested in this question, with lower time limits from ten million to a thousand million years. When Asia, Africa and South America have been as well studied as Europe and North America have been, there will probably be found vast stores of metals, coal, oil and valuable minerals, thus adding to the world's stock of needful things. Also the discovery of new varieties of fossils, the ancestors of living species, especially of mankind, missing links, will add to the interest in human affairs. Geologists have for years been trying to find some