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NATURAL SCIENCE. 



Jan., 



in which the shock was sensible only to delicate seismographs and 

 magnetic instruments. This zone is of immense extent : it includes 

 practically all Europe and large areas in Asia and Africa. There is 

 no reason, however, for placing any terrestrial limit to its expansion ; 

 for a good horizontal pendulum erected at almost any spot on the 

 earth's surface would have registered the passage of the earthquake- 

 pulsations. The time will soon come, we may well hope, when a 

 system of these wonderfully sensitive instruments may be established 

 at certain selected stations all over the world, and we may then be 

 able to trace the pulsations of a great earthquake as they travel round 

 the globe, perhaps more than once, after the manner of the air-waves 

 from Krakatoa in 1883. 



The chief feature of the first three isoseismals is one that 

 characterises those of nearly all severe earthquakes in countries 



Fig. I. — Map of the Constantinople Earthquake. 



where they are frequent and violent — that is, in which the rate of 

 tectonic development is now rapid. This is their extreme narrowness 

 compared with their length. The first isoseismal, for instance, is 175 

 kilometres long and only 39 broad, the second 248 by 74, and the 

 third 354 by 175 kilometres. The natural inference is that the 

 seismic focus is not a point, but of great length and parallel to the 

 axes of the isoseismal lines. 



Nature of the Earthquake and other Phenomena. — At Con- 

 stantinople the earthquake was felt shortly after noon. Mr, Coumbary, 

 the Director of the Meteorological Observatory, gives the time as 

 0.24 p.m. (mean local time). Three shocks were felt in rapid succes- 

 sion, there being hardly any interval between them. The first was 

 the weakest. It was preceded for a second or two by a loud noise, 

 like the rolling of many carriages on a paved road. It was 

 horizontal, lasted four or five seconds, and continually increased in 



