EARTHQUAKES AND OTHER SEISMIC MOVEMENTS. 311 



flexibility, and that, by providing cracks or joints between the parts of 

 buildings which have different periods of vibration, some of the strain 

 might be taken off from them, and they might be made more stable. 

 In stone-work, the cracks have been observed generally to run through 

 the mortar-joints ; in brick-work, through either bricks or mortar, 

 often preferring the bricks. 



As fractures in walls seem most likely to take place above open- 

 ings like doors or windows, it follows that where architecture demands 

 that openings should be placed one above another in heavy walls, 

 there will be lines of weakness running through the openings. As 

 arches are only intended to resist vertical thrusts, special construction 

 must be adopted to make them strong enough to resist horizontal pulls. 

 This might be given by inserting iron girders or wooden lintels in the 

 arches. Mr. Perry, of Tokio, has suggested a plan of building so that 

 the openings of each tier would occupy alternate positions. Such a 

 line is shown in Fig. 4, where the dotted lines run through openings 



\ 



D ,' 

 ti ,ti D 



o;Bo 

 pf n H 



/ 



*'a ^ 



D D 



D D 



43-0 & 



D D 



n ft n 



% \ 



a 



b c\ 



d* 



\ 



/ 



Fig. 3. Brick Buildings in Tokio, showing 



Fractures. 



Fig. 4. 



Fig. 5. 



representing the direction of the lines of weakness. If we compare this 

 with Fig. 5, we shall see that in the case of a horizontal movement, 

 a b, or a vertical movement, c d, fractures would more probably occur 

 in a house built like Fig. 5 than in one built like Fig. 4. If, how- 

 ever, these two buildings were shaken by a shock which had an angle 

 of emergence of about 45, in the direction of ef y the effects might be 

 reversed. Fractures following a vertical line of weakness are shown 

 in the accompanying drawing (Fig. 6) of the church of St. Augustin, 

 at Manila, shattered by the earthquake of 1880. 



When an earthquake shock enters and proceeds along a line of 

 buildings, the last building in the row will, of course, suffer the most, 

 and will exhibit the greatest tendency to fly away from its neigh- 

 bors. If the house stands on the edge of a canal, or cliff, this tend- 

 ency is increased by the similar motion of the escarpment. The fate 

 of an end-building thus stricken is shown in Fig. 7, which is taken 

 from the photograph of a house that was shattered in 1868 at San 

 Francisco. Houses may also be rocked on their foundations, or even 



