364 THE POPULAR SCIENCE MONTHLY. 



very careful consideration of the fractures in walls and other damage, 

 was able to draw a number of interesting conclusions as to the direc- 

 tions and amplitudes of the principal vibrations and as to the site of 

 the center of disturbance. 



Architects should be able, by an adherence to sound mechanical 

 principles, to construct buildings which should stand against all but the 

 severest shocks, and much has already been done in this way. Where 

 a choice for the site of an intended building is possible, the most im- 

 portant consideration is that it should be where there has been the 

 greatest immunity from vibration on previous occasions, for, even with- 

 in a very small area, different spots are very differently affected. In 

 most regions there is only a single important center whence earth- 

 quakes originate, and the safe places are situated in what may be 

 called earthquake-shadow for the prevalent vibrations. For just as 

 a high wall, a hill, or a railway - cutting often completely cuts off 

 sounds by forming a sound-shadow, so a ravine or some arrangement 

 of the geological formation may afford earthquake-shadow for particu- 

 lar places. 



It is not in general possible to pick out the favorable sites by mere 

 inspection, for the distribution of vibration is often apparently capri- 

 cious. Thus Milne tells us of a princely mansion at Tokio " which has 

 so great a reputation for the severity of the shakings it receives, that 

 its marketable value has been considerably depreciated, and it is now 

 untenanted."* 



In a town which is frequently shaken there is no need to wait long 

 to carry out a rough survey with seismographs, and thus to obtain an 

 idea of the relative shakiness of the various parts. If such a survey is 

 impossible, it is best to avoid as the site for building a loose soil, such 

 as gravel, resting on harder strata, and the edge of a scarp or bluff, or 

 the foot of similar eminences.! 



The same capriciousness of distribution, which is observable on a 

 small scale, is found to hold on a large scale when we consider the dis- 

 tribution of earthquakes throughout a whole country. Regions subject 

 to earthquakes, or seismic areas, appear to have fairly definite bounda- 

 ries, which remain constant for long periods. For example, in Japan, 

 earthquakes are rarely felt on the western side of the central range 

 of mountains. 



The search for the actual point whence the earthquake originated is 

 one of the most interesting branches of the science. In order to trace 

 the earthquakes in a country to their origin, the places of observation 

 should not be chosen where there is comparative immunity from shak- 

 ing. Thus a seismic survey is necessary, and the limits of the seismic 

 areas will be discovered in the course of it. Milne commenced his sur- 

 vey of Japan by sending to the local government offices in the impor- 

 tant towns, distant from thirty to a hundred miles from Tokio, packets 



* Milne, " Earthquakes," p. 134. f Ibid., p. 144. 



