1909-] THEIR CAUSES AND EFFECTS. 237 



building forces. Many others in Europe, Japan and America have 

 contributed to the advance of seismology, but particular mention 

 should be made of the services of Professor John Milne, of England, 

 whose long residence in Japan and intimate study of the earthquake 

 phenomena of that and other uneasy regions have enabled him to 

 contribute more than any other one person to the advance of the 

 new science. 



The perfecting of instruments for the purpose of recording 

 movements of every kind in the surface of the earth has vastly 

 extended our knowledge of the character of earth vibrations and 

 enhanced the value of deductions afifecting the theory of earth- 

 quakes. The instrumental study of earthquakes by means of seis- 

 mographs, however, can hardly be said to antedate the year 1892, 

 but within the past decade and a half the number of fully equipped 

 earthquake stations has vastly increased, the growth having been 

 considerably accelerated through the interest aroused by the dis- 

 asters of the last three years. There are now in Great Britain and 

 her colonies fifty seismographic stations equipped with the same 

 type of instrument, while in all the world there are more than two 

 hundred stations equipped with instruments capable of recording 

 world-shaking earthquakes. More than half of these stations are 

 in Europe. 



No large part of the surface of the globe seems to be entirely 

 stable, but certain regions or zones are much more liable than others 

 to the occurrence of earthquakes. If we study a map of the world 

 upon which their location has been plotted, we find in the eastern 

 hemisphere a broad belt of seismic activity extending from west to 

 east through the Mediterranean Sea, Persia, the southern Himalayas 

 and the Sumatra-Java group of islands. A branch zone stretches 

 from the southern end of the Caspian Sea northeastward half way 

 across Asia. This is de Montessus de Ballore's " Alps-Caucasus- 

 Himalayas " belt and it has furnished more than 53 per cent, of 

 recorded shocks.* A seismic belt practically encircles the Pacific 

 Ocean, the principal points in it being the Japanese Archipelago, 

 Alaska, California, Southern Mexico and Central America and the 



* F. de Montessus de Ballore, " Les tremblements de terre," p. 24, Paris, 

 1906. 



