differing but little from Bessel’s (1/299) will be finally adopted. It must, of course, be borne in mind that the spheroid here considered is a spheroid of reference, and that the true geoid may present many irregularities. A question which has much absorbed the attention of geodesists of late years, but which need only be briefly mentioned here, is that of the variation of latitudes, resulting from a periodical shift of the axis of rotation on the surface of the earth. Suspected by Bessel (1817), the variability of latitudes was proved by the researches of Peters (1844) and Nyrén (1873), founded on the observations of Pulkowa; but these astronomers had found only a very slight amplitude (0″·10) in adopting the tenmonths’ period, which seemed pointed to by Euler’s theory. The researches of Clerk Maxwell (1857), Pergola (1872), Downing (1880), Küstner (1888), having once more attracted attention to this subject, in the year 1889 the observatories of Berlin, Potsdam, Prague, and Strasburg concerted a plan for regular determinations of latitude by Talcott’s method; and variations of from 0″·3 to 0″·5 were brought to light. Since then many other observatories have taken part in the work, and a special expedition was sent to Honolulu in 1891. Professor Albrecht every year brings together the results of the gathered observations. From his detailed reports it follows that, since 1890, the pole of rotation of the earth has described an irregular spiral, of variable amplitude, around a mean position from which it does not deviate by more than 0″·3. On the other hand, Mr S. C. Chandler, by a careful discussion of observations from 1825 to 1893, arrived at the conclusion that the latitude variation is composed of two terms, one having a period of 14 months (429 days), the other a mean period of a year, with amplitudes varying from 0″·10 to 0″·20; he thinks the annual component may be elliptical. As to the theoretical question of the causes of these variations, Lord Kelvin has already stated that meteorological influences might be the cause of annual variations so great as 0″·5. M. Radau has further shown[1] that the combination of an annual period with another period, such as the Eulerian one, could result in great amplification of the effects. Finally, Professor Newcomb has explained the existence of the fourteen-months’ period by the influence of the elasticity of the earth. It was for the sake of an exhaustive study of these questions that an “ International Service of Latitudes ” was organized in 1899 by the Geodetic Association in six observatories distributed along the parallel of 39°.
(R. Ra.)
Earthquakes.—Strange as it may appear, the advances that have been made in the study of earthquakes, Attention to seismology. and the world-wide interest shown commenced in Japan. When the Japanese Government, desiring to adopt Western knowledge, invited to its shores bodies of men to act as its instructors, the attention of the newcomers was naturally attracted to the frequent shakings of the ground. Interest in these phenomena increased more rapidly than their frequency, and at length it was felt that something should be done for their systematic study. At midnight on 22nd February 1880 movements more violent than usual occurred; chimneys were shattered or rotated, tiles slid down from roofs, and in the morning it was seen that Yokohama had the appearance of a city that had suffered a bombardment. The excitement was intense, and before the ruins had been removed a meeting was convened and the Seismological Society of Japan established. The twenty volumes of original papers published by this body summarize to a large extent the results of the later study of Seismology.
The attention of the students of earthquakes in Japan was at first directed almost entirely to seismometry or earthquake measurement. Forms of apparatus which then existed, as for example the seismographs, seismometers, and seismoscopes of Mallet, Palmieri, and others, were subjected to trial; but inasmuch as they did little more than indicate that an earthquake had taken place—the more elaborate forms recording also the time of its occurrence—they were rapidly discarded, and instruments were constructed to measure earthquake motion. To describe the varieties of apparatus devised in Japan and their purposes would require a special volume on Seismometry. Slightly modified types of the new instruments were adopted throughout the Italian peninsula, and it is fair to say that the seismometry developed in Japan revolutionized the seismometry of the world. The records obtained from the new instruments increased our knowledge of the character of earthquake motion, and the engineer and the architect were placed in a position to construct so that the effects of known movements could be minimized. It was no doubt the marked success, both practical and scientific, attending these investigations that led the Japanese Government to establish a chair of Seismology at its University, to organize a system of nearly 1000 observing stations throughout the country, and in 1893 to appoint a committee of scientific and practical men to carry out investigations which may palliate the effects of seismic disturbances. In the first year this committee received a grant of £5000, and as liberal sums for the same purpose appear from time to time in the parliamentary estimates, it may be assumed that the work has been fraught with good results. In their publications we find records not only of experiences and experiments in Japan, but descriptions and comments upon earthquake effects in other countries. In two of the volumes there are long and extremely well illustrated accounts of the earthquake which on 12 th June 1897 devastated Assam, to which country two members of the above-mentioned committee were despatched to gather such information as might be of value to the architect and builder in earthquake-shaken districts.
A great impetus to seismological investigation in Europe and America was no doubt given by the realization of the fact that a large earthquake originating in any one Seismological research. part of the world may be recorded in almost any other. Italy for many years past has had its research. observatories for recording earthquakes which can be felt, and which are of local origin, but at the present time at all its fifteen first-class stations we find instruments now given in their phenomena, were initiated in work to record the unfelt movements due to earthquakes origin ating at great distances, and as much attention is now paid to the large earthquakes of the world as to the smaller ones originating within Italian territory. The Kaiserliche Akademie der Wissenschaften of Vienna has established earthquake observatories in Austria, and the Central Observatorium of St Petersburg has carried out similar work in Russia. Germany, at a cost of £3500 and with an annual allowance of £295, has attached a seismological observatory to its university at Strassburg, whilst provision has been made for a professorship of Earth Physics at Gottingen. In accordance with the recommendation of the British Association of Great Britain, seismographs of a similar character have been installed at the following places :—Isle of Wight, Kew, Paisley, Toronto, Victoria (B.C.), Philadelphia, Mexico, Trinidad, Arequipa, Cordova in Argentina, New Zealand, Hawaii, Japan, Java, Calcutta, Madras, Bombay Mauritius,
- ↑ Comptes Rendus, t. cxi., 1890.
