Geological magazine . iginalposition, but before the movement is completed, disturbances fromsucceeding spheres will reach the point P, and will affect itssubsequent motion, though not the vibratory character of that motion. Hence, remembering that the earths crust is seldom or never quitehomogeneous and isotropic, that the seismic focus may be of anyform and magnitude and may even consist of detached portions, thatthe disturbances at different points of the seismic focus are notnecessarily of equal intensity, and that the disturbances do notnecessarily take place simultaneously throughout the
Geological magazine . iginalposition, but before the movement is completed, disturbances fromsucceeding spheres will reach the point P, and will affect itssubsequent motion, though not the vibratory character of that motion. Hence, remembering that the earths crust is seldom or never quitehomogeneous and isotropic, that the seismic focus may be of anyform and magnitude and may even consist of detached portions, thatthe disturbances at different points of the seismic focus are notnecessarily of equal intensity, and that the disturbances do notnecessarily take place simultaneously throughout the whole extent ofthe seismic focus, it is evident that we have a cause sufficient to pro-duce any vorticose shock however complicated, and any variety inthe changes of direction. It will be seen also that the same reasoning may be applied toearth-waves consisting of transverse vibrations, whether thesevibrations are executed in straight lines or curves. As an illustration, let us take the case of a seismic focus (drawn.
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