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Page 20 - ... solar system to a period not much exceeding some twenty millions of years ; and many of our geological friends protest against so scanty an allowance. The same theory would give us, perhaps, half as much time for our remaining lifetime ; but this is no objection, since I perceive no reason to doubt the final cessation of the sun's activity, and the consequent death of the system.
Page 286 - Societies, v. 2, p. 113. as much water as the present channel can take. At all points below Cairo, it is now pretty well known how much more water would have passed in a confined channel, than did so pass in the flood of 1882. With such facts as a basis for estimates, engineers still differ very widely as to the necessary height the levees must have to confine these additional volumes. Some engineers affirm that the levees need be but little, if any, higher than they now are, while others insist...
Page 13 - Its satellite system deserves careful observation, especially in respect to the eclipses, since we find in them a measure of the time required for light to cross the orbit of the earth, and so of the solar parallax ; and also because, as has been already mentioned, they furnish a test of the constancy of the earth's rotation. The photometric method of observing these eclipses, first instituted by Professor Pickering at Cambridge in 1878, and since re-invented by Cornn in Paris, has already much increased...
Page 10 - But they, no doubt, render it considerably probable that such alterations have occurred, and are still in progress, and they justify a persistent, careful, minute, and thorough study of the details of the lunar surface with powerful instruments : especially do they inculcate the value of large-scale photographs, which can be preserved for future comparison as unimpeachable witnesses. I will not leave the moon without a word in respect to the remarkable speculations of Professor George Darwin concerning...
Page 15 - ... great as to render quantitative calculations unsafe, and make positive conclusions more or less insecure. We can pretty confidently infer the presence of iron and hydrogen and other elements in the sun by appearances which we can reproduce upon the earth; but we cannot safely apply empirical formulae (like that of Dulong and Petit, for instance), deduced from terrestrial experiments, to determine solar temperatures: such a proceeding is an unsound and unwarrantable extrapolation, likely to lead...
Page 93 - Nature" (July 3, 1884, page 230), gives some of the results of his recent investigation of gases subjected to electrical discharges, and believes himself justified in making the following hypothesis : " In a gas the passage of electricity from one molecule to another is always accompanied by an interchange of the atoms composing the molecule ; the molecules are always broken up at the negative pole,
Page 88 - In thus looking for the seat and origin of electrical action, how much have we discovered? It is evident that our knowledge of electricity will increase with our knowledge of molecular action, and. our knowledge of molecular action with that which we call attractive force. It is somewhat strange that, although we are so curious in regard to electricity, we seldom reflect that gravitation is as great a mystery as electrical attraction. What is this force which acts instantly through space, and...
Page 17 - Our storms travel toward the east,while the volcanic dust from Krakatoa moved swiftly west. We may at least conjecture that the difference between different planets somehow turns upon the question, whether the body whose atmospheric currents we observe is receiving more heat from without than it is throwing off itself. Whatever may be the true explanation of this peculiarity in the motion of sun-spots, it will, when reached, probably carry with it the solution of many other mysteries, and will arbitrate...