194 ANNUAL KEPOET SMITHSONIAN INSTITUTION, 19 34 



interest in the subject was roused by his experience of earthquakes 

 during the period 1876 to 1895 when he was professor of mining 

 and mineralogy in Japan. The subject was also taken up by workers 

 in Germany and Italy about the same time, and very soon various 

 types of apparatus were devised to record earthquakes at great 

 distances. On his return to England in 1895 Milne set up his own 

 earthquake observatory at Shide in the Isle of Wight, and in 1897 

 he inaugurated a scheme whereby recording instruments were 

 installed at a number of stations in various parts of the globe, 

 The observatory at Shide became the central office of a world-wide 

 seismic survey, and the comparative data thus obtained soon laid 

 bare the main facts regarding the propagation of earth tremors 

 through and round the world. A great advance was made at 

 the beginning of the present century, when Wiechert and his pupils 

 at Gottingen took up the question of the interpretation of seis- 

 mograms both from the observational and the theoretical side, 

 and showed how the results lead to a knowledge of the physical 

 properties of the earth. When Milne died in 1913, the organization 

 which he had built up passed into the hands of the late Prof. 

 H. H. Turner, who had shared Milne's enthusiasm in the work for 

 many years. In addition to his other duties Turner found time 

 for much research in seismology, notably on earthquake periodicities 

 and ieep earthquakes, and his interest in the subject lasted righ^ 

 up to the last conscious minutes of his life, for the collapse which 

 led to his death occurred while he was in the presidential chair of 

 the International Seismological Association at the Stockholm Con- 

 gress in August 1930. 



Progress in seismology is dependent to a very large extent on 

 international cooperation, and for this reason alone the subject is 

 deserving of all the support we can give it. Since the war the 

 number of observing stations in the world-wide network has in- 

 creased nearly threefold; at the present time there are nearly 400. 

 Practically every country in the world takes a share in the obser- 

 vations. The work, started by Milne and continued by Turner, of 

 collecting data and issuing a summary of the results is still under- 

 taken in England, at the University Observatory, Oxford, under 

 the auspices of the British Association. In addition to the routine 

 work of recording and measuring earthquakes a large amount of 

 seismological research is now being done in many countries, and 

 this is leading to an increased knowledge of the properties of the 

 earth. 



HOW EARTHQUAKES OCCUR 



The earth's crust has by no means reached a stable state ; it is con- 

 tinually undergoing deformation under the influence of stresses 



