Earthquakes and Volcanoes
"Oh! how I wish I could feel an earthquake!" is generally among the first exclamations of the newly-landed European. "What a paltry sort of thing it is, considering the fuss people make about it!" is generally his remark on his second earthquake (for the first one he invariably sleeps through). But after the fifth or sixth he never wants to experience another; and his terror of earthquakes grows with length of residence in an earthquake-shaken land, such as Japan has been from time immemorial. Indeed, geologists tell us that much of Japan would never have existed but for the seismic and volcanic agency which has elevated whole districts above the ocean by means of repeated eruptions.
The cause of earthquakes remains obscure. The learned incline at present to the opinion that the causes may be many and various; but the general connection between earthquakes and volcanoes is not contested. The "faulting" which results from elevations and depressions of the earth's crust, the infiltration of water to great depths and the consequent generation of steam, the caving in of subterranean hollows-hollows themselves pro duced in all probability by chemical degradation-these and other causes have been appealed to as the most probable. One highly remarkable fact is that volcanic and earthquake-shaken regions are almost always adjacent to areas of depression. The greatest area of depression in the world is the Pacific basin; and accordingly round its borders, from Kamchatka through the Kuriles to Japan, thence through a line of small islands to the Philippines and to Java, then eastward to New Zealand, and right up the western coast of South America, is grouped the mightiest array of volcanoes that the world contains. Another fact of interest is the greater occurrence of earthquakes during the winter months. This has been explained by Dr. Knott as the result of "the annual periodicity of two well-known meteorological phenomena-namely, snow accumulations over continental areas, and barometric gradients."
Japanese history is a concatenation of earthquake disasters, exceeded only by those which have desolated South America. But the Japanese people had perforce submitted to these ravages, without attempting to investigate the causes of earthquakes scientifically. All they had done was to record anecdotes and superstitions connected with the subject, one of the most popular of which latter (popular indeed in many parts of the world besides Japan) is that earthquakes are due to a large subterranean fish, which wriggles about whenever it wakes up. Another notion commonly entertained, and embodied in the following doggerel verse, is that certain other occurrences can be foreknown from the hour at which a shock takes place:-
Ku wa yamai Go shichi ga ame ni Yotsu hideri Mutsu yatsu-doki wa Kaze to shiru-beshiWhich may be Englished as follows:
At twelve o'clock it means disease, At eight or four 'tis rain,
At ten 'tis drought, while six and two Of wind are tokens plain.
With the advent of the theoretically minded European, a new era was inaugurated. A society named the Seismological Society of Japan was started in the spring of 1880, chiefly through the efforts of Professor John Milne, F.R.S., who has ever since devoted all his energies to wrestling with the problems which earthquakes, earth oscillations, earth currents, and seismic and volcanic phenomena generally, supply in such perplexing quantity. The Japanese government, too, has lent a helping hand by the establishment of a chair of seismology in the Imperial University, and of several hundreds of observing stations all over the empire,-an empire, remember, dotted with no less than fifty-one active volcanoes, and experiencing about five hundred shocks yearly.
Can earthquakes be prevented? If they cannot be prevented, can they at least be foretold? Both these questions must unfortunately be answered in the negative. Still, certain practical results have been arrived at by Mr. Milne and his fellow-workers, which are by no means to be despised. It is now possible to make what is called a "seismic survey" of any given plot of ground, and to indicate which localities will be least liable to shocks. It has also been shown that the complete isolation of the foundations of a building from the surface of the soil obtains for the building comparative immunity from damage. The reason is that the surface shakes more than the adjacent lower layers of the soil, just as, if several billiard-balls be placed in a row, an impulse given to the first one will make only the last one fly off, while those in the middle remain nearly motionless. For the same reason, it is dangerous to build near the edge of a cliff. To architects, again, various hints have been given, both from experience accumulated on the spot, and also from that of Manila and other earthquake-shaken localities. The passage from natural to artificial vibrations being obvious, Professor Milne has been led on to the invention of a machine which records, after the manner of a seismograph, the vibrations of railway trains. This machine keeps an automatic record of all the motions of a train, and serves to detect irregularities occurring at crossings and points, as also those due to want of ballast, defects in bridges, and so on.
Thus, imperfect as it still is, imperfect as the nature of the case may perhaps condemn it always to remain, the science of seismology has already borne practical fruit in effecting a saving of tens of thousands of dollars. To those who are interested in seismometers and seismographs, in earthquake maps and earthquake catalogues, in seismic surveys, in microseisms, earth tremors, earth pulsations, and generally in earth physics, we recommend a perusal of the Transactions of the Seismological Society of Japan, complete in sixteen volumes, of its continuation, the Seismological Journal of Japan, and of the volume entitled Earthquakes, by Professor Milne in the "International Scientific Series". Volume IX. Part II. of the Seismological Transactions is specially devoted to the volcanoes of Japan, and contains a mass of statistics, anecdotes, historical details, and illustrations,-each individual volcano, from the northernmost of the Kuriles down to Aso-san in Kyūshū, which has the largest crater in the world, being treated of in detail. The Ansei Kembun Roku and the Ansei Kembun Shi are capitally illustrated Japanese accounts of the great earthquake which wrecked Yedo in 1855. Lovers of the ghastly will search long before they find anything more to their taste than the delineations there given of men and women precipitated out of windows, cut in two by falling beams, bruised, smashed, imprisoned in cellars, overtaken by tidal waves, or worse still, burnt alive in one of the great fires caused by the sudden overturning of thousands of candles and braziers all over the city. Truly these are gruesome books.