EARTHQUAKES ANOTHER EARTH MOVEMENTS.

Wairarapa Daily Times, Volume VIII, Issue 2389, 2 September 1886, Page 2

EARTHQUAKES ANOTHER EARTH MOVEMENTS.

Undor tho above title, a book has been published by Professor John Milne, Profeasor of Mining and Geology in the Imperial College of Tokio, Japan. We extract a portion of of tho work, which appears In theJHterrary World;—'! Researches byjhe>f(l cf Instruments, and otherwise,: have shown that an earthquake Is not to be regarded as consisting of a single shock, but that, typically it consists of " a aeries of small tremors, succeeded by a shock, or series of shocks separated by more or less irregular vibrations.of the ground." In othei words, it is apulso-like motion propagated through solid ground; in the'same way aa a sound i» propogated through the air. To help in the study of artificial earthquakes have been produced by the experiment.of letting a heavy weight fall from a height.tojthe ground, or by exploding dyimunto iii a bore-hole j These experiments showed that the,' presence of both hills and : pondgpjjuj especially of tho latter, had an ehwin limiting the disturbance. But the moßt reliable information has" been obtained from, the observation of natural earthquakes, and some matters connected with them could, of course, only be determined inthis way. Thus, for'instanco, only from an actual earthquake';could the time that such "convulsions'.' njay cover be known. Tradition tells of a Japanese earthquake in A.D. 977, lasting 300 days. In New Zealand, in, loMßisliock»jtfMy numbering 1000 a day, _ contrnHKor nearly five weeks. The' limiting ofiSct of mountain ranges; too," has been signally illustrated by actual earthquakes. On one side of range of mountains cities have laid inruhiß, while on the other side the earthquake has Mt.even beon felt, The velocity of an earthquake is a matter of importance, as enabling investigators to trace its spot of oris»in;. tho varying velocities of one evthquako in Japan ■were placed betwbe'n 40QO.and • 9000 feet por second. Passing byjprae interesting ■ chaptora on seaquakos, and other allied topics, we come to an interesting chapter on tho causes of earthquakes. The chief of these are to bo sought within thimtom of the oarth itself, and not in solar and lunar iufluenco, or in variations of atnwaphoric pressure. Tho majority of them are attributable to '• explosive efforts at at volcanic foci." Most of these oxplosions are Bubmarino, and are brought about by a sudden inrush of water through fissures into heatod rock within the earth. The sadden formation of these fissures or faults is due, in' many cases, to alterations in the distribution of telluric heat and the atactics force, of gravity. But earthquakes majiw>so result through underground the result of chemical proceaios; in time a hollow cavern is formed of. which the roof gives way. And they might oome through the breakhig of the earth's crust through sheer addition of superincumbent weight, as in the accumulation of water by rising tides, or in added "atmospheric pressure.