Page:Popular Science Monthly Volume 29.djvu/325

 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 openings 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



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 e f, 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 neighbors. If the house stands on the edge of a canal, or cliff, this tendency 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