THE GROWTH OF A PLANET.*
Me. GREW has to take us back into a very obscure region indeed when he asks the question, " How did our earth come gnto being P " He discusses Laplace's nebular hypothesis and that of the spiral nebulae, to which he is himself inclined. As we read what amazing, we may say what disturbing, state- anents do we encounter! What would happen if two solar systems approached sufficiently for one to capture an outer planet of the other ? And we know that all the heavenly bodies are moving at a great speed. "If the approach of the Solar systems left nothing greater than 50000,000- miles between their centres . . . it might, and would probably, lead to the fall of some disturbed planet on to one of the interior suns. Then would follow an overwhelming outburst- of heat." Such, perhaps, we have seen in the- flaming-up of the star Tau Corona some forty years ago. We reach a little more light when we come to "Planetary Analogies." The other bodies of our system tell us little, but the Moon and Mars are fruitful of fact and speculation. Mr. Grew is doubtful, to say the least, about Professor Lowell's Martian theories, and the canals especially, as the work of a highly civilized race, pathetically contending against hostile condi- tions. When we come to the Earth itself we have some facts indeed, but nothing approaching what we should like to have. 'There are theories as-to the heat of the Earth in its earliest history. What do we know- of its heat now ? Very little. The deepest boring we have is less , than two miles deep, and it would cost £5,000,000 to reach twelve miles and take 84 years. What temperature should we .find? Possibly one of something like 800°F. Mr. Grew treats successively of the Earth's shape, of volcanic action, of the atmosphere—its 'history and its present condition—and of the ancient sea. 'This brings him to the. most fiercely disputed of all Earth -questions—the origin of life. One can hardly help thinking that it is best left alone. Perhaps the ingenious theorist who -declared that it came to us from some other planet had an ironical intention of suggesting as much. Mr. Grew has much to tell us of the various activities which the word .connotes, and 'at last brings us to Man. This is, perhaps, the most interesting. chapter in a highly interesting volume, taking ass from the Pithecanthropus erectus down to the most highly -developed Neolithic races. We notice in passing that our author is, on the whole, inclined to accept Mr. Benjamin Harrison's Eoliths. Would our readers like to be left with a sensation 'There is a Very small amount of carbon dioxide in the air. Were. this to disappear 'all life would perish ; were it to be increased—amore possible suggestion—man and all the air- breathing creatures would meet the same fate.
• The Growth of a Banat. By Edwin Sharpe Grew. London: Methuen and %Cie. 165.]
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