Another point of importance would be to build archways _curving_ into the supporting buttresses; the archways over doors and windows which we find in earthquake countries do not appear to be in any way different from those which are built in countries free from earthquakes. In the one country these structures have simply to withstand vertical pressures applied statically; in the other, they have to withstand more or less horizontal stresses, applied suddenly. _Relation of Destruction to Earthquake Motion._—The relations which exist between the overturning and projection of bodies and the motion of the ground have already been discussed. It may be interesting to call attention to the fact that in the formulæ showing three relationships, it was the _shape_ rather than the _weight_ of a body which determined whether it should be overturned or projected by a motion at its base. As an interesting proof that light bodies may be overturned as easily as heavy ones. Mallet refers to the overturning of several large haystacks as one of the results of the Neapolitan earthquake. If masses of material are displaced or fractured, then Mallet remarks _____ that the maximum velocity will exceed √2_gh_, where _h_ is the amplitude of the wave. Should the maximum velocity be less than this quantity, the masses which are acted upon will be simply raised and lowered, and there will be no relative displacements even if the emergence of the wave be nearly or quite vertical. When we get a vertical wave acting upon an irregular mass of masonry, the heavier portions of the masonry, by their inertia, tend to descend relatively to the remaining portions, and in this way vertical fissures will be produced. For this reason it would not be advisable to use heavy materials above archways, heavy roofs, or heavy floors. The vertical fissures, Mallet remarks, would have their widest opening at the base. In considering cases of fracture produced by earthquake motion, it must be remembered that these are due to stresses applied _suddenly_, and that if the same amount of stress had been _slowly_ applied to a building, fractures might not have occurred. If a disturbance is horizontal, and has a direction parallel to the length of a wall, the wall is carried forward at its foundations. This motion is opposed by the inertia of the upper portion of the wall and the various loads it carries. The wall being elastic, distortion takes place, and cracks, which are widest at the top, will be formed. In a uniform wall the two most prominent fissures ought to be near the ends. If the horizontal backward and forward movement has a direction oblique to the plane of the wall, the wall will be either overthrown, fractured, or have a triangular fragment thrown off towards the origin from the end last reached.