Page:Popular Science Monthly Volume 29.djvu/326

312 quite overturned, as appears to have happened to the stud-mill at Hayward, California (Fig. 8).

In any building which may be affected by an earthquake, we have to consider the vibration of a number of parts, the periods of which, if they were independent of each other, would be different. On account of this difference in period, while one portion of a building is



endeavoring to move toward the right, another is pulling toward the left, and either the bonds which join them or the parts themselves will be strained or broken. This was illustrated by many of the chimneys in the houses at Yokohama, which, in the earthquake of February 20, 1880, were shorn off just above the roof. Since then, builders have learned to let chimneys pass freely through the roof without coming in contact with any of the main timbers.

In trying to make structures earthquake-proof, we may build our house weak and flexible, so that the shock shall pass over it as the wind over a reed, or we may attempt to make it stronger than the shock. The native Japanese houses, with their flexible framing, are built on the former plan; some of the European houses essay the