Page:Great Neapolitan Earthquake of 1857.djvu/480

But where the are of horizontal rotation is great, as it is in this instance, where the chimney was twisted round 30° to the westward, the latter must have been extremely small or nil.

Calling these two small corrections $d$ and $f$, the whole interval in time ${\text{I}}$, between the shocks is

$I=T+{\frac {T}{2}}+d+f.$

We therefore obtain

$I=1.536+{\frac {1.536}{2}}+d+f.$

or without the two latter,

$I={\text{1.7304 seconds,}}$

and estimating $d$, assuming $f$ as small $=0$, we may consider

$I={\text{1.75 seconds.}}$

This is the difference in time, between the arrival of the two shocks; both of which started at the same moment and from the same origin. The evidence for the position of the latter has yet to be adduced; anticipating the fact, however, the Certosa, is distant from it, ⁠16+1/2⁠ geographical miles, or 33,415 English yards in the right line, which was the path of the second shock, arriving directly 15° W. of north to south, through the deep clays and gravels, &c., of the Vallone; while that of the first shock, was through the east lateral range of solid limestone mountains, but whose length (as respects the wave-path) we may consider as one-fifth of a mile greater.

From facts (also yet to be adduced), I found that the general velocity of translation of the wave of shock, through the limestone country, was at the rate of 240 yards per