3 io THE POPULAR SCIENCE MONTHLY, 



four millimetres. Mallet believes that the displacement may in some 

 instances be equal to a foot ; and M. Abella records a rough observa- 

 tion, in the Philippine Islands, of a motion of the earth to a distance 

 of two metres, when fissures were formed, and seen to open and 

 shut. The velocity of propagation of the wave may vary, even in 

 the same country, between several hundreds and several thousands 

 of feet per second. The same earthquake travels faster across dis- 

 tricts near to its origin than it does across districts which are far re- 

 moved ; and, the greater the intensity of the shock, the greater is 

 the velocity. 



If we were suddenly placed among the ruins of a large city which 

 had been shattered by an earthquake, it is doubtful whether we should 

 at once recognize any law as to the relative position of the masses of 

 rubbish and the general destruction around. The results of observa- 

 tion have, however, shown that, among the apparently chaotic ruin 

 produced by earthquakes there runs more or less of law governing 

 the position of bodies which have fallen, the direction and position of 

 cracks in walls, and the other effects. Usually, walls of buildings at 

 right angles to the shock will be more likely to be overthrown than 

 those which are parallel to it. It is said that in Caracas every house 

 has its lado securo, or safe side, where the inhabitants place their fra- 

 gile property. It is the north side, and has been chosen because about 

 two out of three destructive shocks traverse the city from west to 

 east, so that the walls in those sides of the building take them broad- 

 side on. This appears to be the rule in destructive earthquakes. But, 

 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 backward 

 and forward as a whole, and there is little or no tendency for them to 

 be fractured at their weaker parts. The walls, however, which are 

 parallel to the direction of the movement are extended and contracted 

 along their length, and may consequently be expected to give way 

 over the door- and window-openings. The results of the examination 

 of more than three hundred foreign-built brick houses in Tokio, Japan, 

 all similar in their construction, are typically illustrated in Fig. 3. 

 They show that in the upper windows nearly all the cracks ran from 

 the springing of the arches, which formed an angle with the abutment. 

 In the lower arches, which curved into the abutments, not a single 

 crack was observed at the spring-way. The cracks in those arches 

 were near the crown, where beams projected to carry the balcony ; 

 and in many instances they proceeded from such beams, even if there 

 were no arches beneath. The houses which were most cracked were 

 in the streets running parallel to the direction in which the greater 

 number and most powerful set of shocks cross the city. From the 

 fact that cracks once made in a building did not appear to extend 

 under the repetition of shocks similar to the one that produced them, 

 it has been inferred that buildings thus cracked acquire a degree of 



