The Pacific Unitarian Volume 14-15 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1905 Excerpt: ...earthquakes. On the purely scientific side, the study of earthquakes is of very great interest and importance. It is well known that the vibrations of a great earthquake travel to the remotest part of the globe, and that sensitive instruments for recording such vibrations are in service at many stations throughout the world. The mass of data of this kind is great and rapidly increasing, and although physicists are not yet in agreement as to its interpretation, light is gradually being thrown upon some of the fundamental problems of earthphysics. Among these problems is the question, long debated among geologists and physicists, as to the nature of the material composing the earth's interior mass. Apart from their bearing upon such fundamental questions, however, these long-distance records are of great interest in themselves. It is found that they nearly always possess certain definite characteristics which to the expert are highly significant. One thing proved by these records is the existence of several distinct kinds of earth-waves or vibrations which travel at different speeds. Thus on April 18th. about 13 minutes after the people of California were shaken the "first preliminary tremors" were recorded at Birmingham, England, and about 10 minutes later began the "second preliminary tjremors," of much greater amplitude than the first. After another 10 minutes the "principal portion" began, consisting of vibrations of far greater amplitude than the preceding, and for nearly two hours longer the record showed oscillations of pronounced though decreasing magnitude. These waves travel in every direction from the center of disturbance, and about an hour and forty-three minutes after the principal waves reached Birmingham by the mo...