CHAPTER XIII.
OF THE AMPLITUDE OP THE WAVE AND THE WORK STORED UP IN IT.
Let (Fig. 352) be a section vertically, at the earth's surface, the mean focal point, at the depth , measured
Fig. 352.
upwards upon the seismic vertical , and be the amplitude of the wave, in its path of emergence at , taken somewhere near . The wave is originated by the sudden compression, of the elastic materials forming the walls of the focal cavity. Admitting the temperature, as just obtained on the commonly-assumed hypogeal increment, we have obtained a measure, of the pressure producing this compression; and if we possessed the coefficient of compression