98 EARTHQUAKES. 



Cracks in Buildings, — Eesults like the above come 

 from destructive earthquakes rather than from movements 

 such as those we have to deal with ordinarily. When a 

 building is subjected to a slight movement it is assumed 

 that the walls at right angles to the direction of the shock 

 move backwards and forwards as a whole, and there is 

 little or no tendency for them to be fractured at their 

 weaker parts, these weaker parts being those over the 

 various openings. The walls, however, which are parallel 

 to the direction of the movement are, so to speak, extended 

 and contracted along their length, and in consequence 

 they may be expected to give way over the various open- 

 ings. This tendency for extension and contraction of a 

 wall along its length may be supposed, for instance, to be 

 due to the different portions of a wall, owing to differences 

 in dimensions and elasticity, having different periods of 

 natural vibration, or possibly for two portions of a long 

 line of wall to be simultaneously affected by portions of 

 waves in different phases. 



As an illustration of the giving way of a building in 

 the manner here suggested we may take the case of a 

 large brick structure which was recently being erected in 

 Tokio. This building, at the time of the earthquake, was 

 only some fourteen or fifteen feet above the surface of the 

 ground. The length of the building stretched from N.W. 

 to S.E., and it was intersected by many walls at right 

 angles to this direction. Through all the walls of this 

 building there were many arched openings. In the 

 central part of the transverse walls, which walls were 

 fully five feet in thickness, the arches which joined them 

 together were 4 feet 4 inches in thickness. The arches 

 therefore formed a comparatively lightly constructed link 

 between heavy masses of brickwork. 



On March 3, 1879, at 4.43 p.m., an earthquake was 



