Page:Great Neapolitan Earthquake of 1857.djvu/483



proceed to consider the angle of intersection in an horizontal plane, made by these two shocks at the Certosa. Referring again to the two great stone balls (one along with its base) projected from the top of the Campanile upon the roofs of the front square, (Fig. 1 Diagram No. 238 and Diagram No. 240, and Photog. No. 227 (Coll. Roy. Soc.) in which the ball B is seen lying, where it fell), we are enabled from these to infer the wave-path of the first shock with some certainty.

Both balls were projected from the Campanile in a direction 64° W. of north, and precisely alike.

The first shock, arriving from somewhere between north and east, caused the Campanile to oscillate from west to east and east to west; i. e. in the line of its narrowest dimension of base.

The balls were thrown off in the second semiphase of the wave; therefore, and as the time of oscillation of the tower (from its altitude) was large, and greater than that of the whole phase of the wave they were projected with a velocity less than that due to the shock; the top of the tower 2em