110 EARTHQUAKES. 



Prevention of Fractures. — One conclusion which may 

 perhaps be drawn from these observations is, that a 

 cracked building at the time of an earthquake shows a 

 certain amount of flexibility. Whether a building which 

 had been designed with cracks or joints between those 

 parts which were likely to have different periods of vibra- 

 tion would be more stable, so far as earthquake shakings 

 are concerned, than a similar building put up in an 

 ordinary manner, is a matter to be decided by experi- 

 ment. Certainly some of the cracks which have been 

 examined indicate that if they had not existed, the strain 

 upon the portion of the building where they occur would 

 have been extremely great. 



Direction of Cracks. — In looking at the cracks pro- 

 duced by small earthquakes it is interesting to note the 

 manner of their extension. The basements of the 

 buildings which have been most carefully examined are, 

 for a height of two or three feet, built of large rectan- 

 gular blocks of a greyish-coloured volcanic rock. In 

 these parts the cracks pass in and out between the joints 

 of the stone, indicating that the stones have evidently 

 been stronger than the mortar which bound them to- 

 gether, and as a consequence the latter had to give way. 

 Above this basement when the cracks enter the brickwork, 

 they no longer exclusively confine themselves to the 

 joints, but run in an irregular line through all they meet 

 with, sometimes across the bricks and sometimes through 

 the mortar joints. In places where they have traversed 

 the brickwork, we can say that the mortar has been 

 stronger than the bricks. This traversing of the bricks 

 rather than the joints is, I think, the general rule for 

 the direction of the cracks in the brickwork of Tokio 

 buildings. 



The Pitch of Roofs, — From observation of the effects 



