EFFECTS PEODUCED UPON BUILDINGS. 107 



bably the most important function to be considered. 

 The method of applying the directions of emergence, 

 deduced from observations on fractures, to determine the 

 origin of a disturbance will be referred to in Chapter X. 



Mallet observed that, although two ends of a building 

 might be nearly the same, the fissures and joints do not 

 occur at equal distances from the ends, nor are they 

 equally opened. 



The end where the joints are the most opened is that 

 which was first acted upon, and this phenomenon may be 

 sufficiently well pronounced to indicate the direction in 

 which we must look to find the origin of a disturbance. 

 Amongst possible explanations for this disposition of frac- 

 tures in a wall. Mallet suggests that they may be due to 

 real differences in the two semiphases of the wave of 

 shock, the second semiphase being described with a some- 

 what slower velocity than the first. This, it will be ob- 

 served, is contrary to the indications of seismographs. 



Fig. 19, of the cathedral at Patemo, shows the effect 

 of a subnormal shock striking a wall obliquely and pro- 

 jecting one of its corners. 



MEASUREMENTS OF THE RELATIVE MOTION OF PARTS OF A 

 BUILDING AT THE TIME OF AN EARTHQUAKE. 



In 1880 a series of observations was made in Tokio 

 to determine whether at the time of an earthquake the 

 various parts of the arched openings which we see in many 

 buildings synchronised in their vibrations, or, for want ol 

 synchronism, were caused to approach and recede from 

 each other. The arches experimented on were heavy 

 brick arches forming the two corridors of the Imperial 

 College of Engineering. The direction of one set of these 

 corridors is N. 40° E. and that of the other N. 50° W. 



