Transactions Volume 13-14 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1889 edition. Excerpt: ... that they are actually tipped and rocked, may be derived from the accounts of almost all large earthquakes. (See note on Vertical Motion.) For the Neapolitan earthquake of 1857, Mr. Mallet made many determinations of maximum velocity, many of which were based upon projection phenomena. The mean of these may be taken at about 12 feet per second. The amplitudes of motion, which we will assume were true amplitudes, varied from 2.5 to 4.7 inches, the mean of which may be taken at 3 inches. With these data we can calculate that the period of a wave was 0.125 second, or that there were 8 waves per second. Inasmuch as observation in Japan has shown that the period of a wave increases with its amplitude, and that earthquakes in Japan have often been recorded with periods of over 1 second, it would seem that the above result must be received with caution. The chief source of error probably lies in the fact that the objecis which were projected were thrown farther than they would have been thrown had the supports on which they rested been absolutely rigid. The result of this has been that the maximum velocity as calculated for the ground has been too high. In disturbances produced by the explosion of dynamite it has been shown that the maximum velocity determined by the projection of a ball from the top of a post has been much greater than that yielded by the analysis of a diagram taken by a seismograph at the foot of the post. (Seismic Experiments, Trans. Seis. Soc. Vol. VIII., p. 70.) 12.--Relative Motion Of Neighbouring Points Of Ground. Very little information exists as to how far two points of ground which are near to each other synchronize or disagree in their phase of motion. From a few experiments made in Japan it seems that the heads of...