# Great Neapolitan Earthquake of 1857/Part II. Ch. XV

Chapter XV.
Further Discussion of Observations Made at the Certosa and at Padula.
At Padula, while the main wave-path was unmistakably 17° W. of north to south, I found fissures giving extremes of directions from 155° E. of north to 166° E. of north, and evidences of a very subordinate vibration nearly from west to east. The latter, it is highly probable, was due to the partial dispersion of the main wave of shock, as it reached the southern head of the great valley, and passed from its deep formations out into the limestone mountains that shut it in to the south.
I had also evidences of such subordinate movements, and more distinctly marked, at the Certosa.
The great fissures here, by the very construction of the buildings, ran principally east and west, and north and south; the former being by much the wider (transverse to the main shock), but the abutting of the several masses of building upon each other, very generally preventing that freedom of motion, that is essential to enable deductions as to wave-path to be made thus with precision. From some of the main buildings, that rose free and unencumbered above the level of the surrounding ones, however, I obtained measures of direction, the extremes being 116° E. of north to 165° E. ​of north; and although very wide in limit, and often perplexed, from the complicated movements to which this place had been subjected, all were confirmatory of the general wave-path obtained at the Francescani already given.
The most instructive fissures I found, were those by which the two great gable walls of the refectory had parted off from the ends of the semicircular vault which formed the roof. An interior Photog. of this noble hall is given (No. 229, Coll. Roy. Soc.). The soffit of the vault was fissured in a north and south direction from end to end nearly, and half to one inch wide.
The gables were great semicircular walls of rubble stonework, run up from the chord-line or level of the springing, after the vault had been turned, and merely closed in against the ends of the arch, as in Fig. 239, not being bonded into it. Each of these gable walls had gone out at top from the end of the vault, producing a gradually widening and tremendous fissure, which, at the north end, was open 5 inches at top, and at the opposite, or south end, 3 to 3 1/2 inches.
The gables, thick, heavy, inelastic, and yielding, from the bad rubble of which they are built, had bent over from above the chord-lines, showing innumerable minor thread-like fissures of dislocation in the work, more or less horizontal; neither had approached within some inches of the ​limit of stability. The north gable wall had given out in the first semiphase of the shock, the south in the second semi-phase; and both appeared, from the fragments fallen into the fissures, none of which were crushed, or gripped and pressed into compacted powder, (as is not unusually the case,) to have gone out very little, if at all further, by the impressed movement, than where they stood as I examined them.
The width of this north fissure, therefore, affords an approximate measure, of the actual amplitude of the main wave of shock here; for the opening, or the actual movement of the gable, at the level of its centre of oscillation, upon the chord as axis, must have been about equal to the amplitude of the wave, taken in a horizontal line. It would be useless, upon inexact data, to pursue this minutely; we may conclude, however, that the horizontal amplitude of the main wave of shock here, did not much exceed 4 inches.
There were also immense fissures, in the 9-inch brick groining of the roof of the church, both longitudinally and transversely through the axis. The beautiful domed cupola also presented complicated fissures, but was in so tottering a condition as to prevent close examination; all these indicated a principal wave-path some degrees W. of north to south.
The urn or vase, thrown from the summit of one of the gate-piers, in the garden of the Priure, Photog. No. 230 (Coll. Roy. Soc.), and Figs. 1, 5, and 6, Diagram No. 240, presented a good example, of the high velocity with which bodies thus placed on the summits of slender vertical erections, may be projected by the elastic vibration or rocking communicated by the shock to the erection itself. This vase was thrown nearly in the same path as the balls ​from the Campanile, but in the opposite direction. Its path was 58° W. of north to south.
It was, no doubt, thrown off by the recoil of the pier upon which it stood, when making its second oscillation, produced by the first shock (41° 30′ E. of north to south), when the main shock reached it, which increasing the movement already impressed, and at the same time changing the plane of projection, threw it to an horizontal range of 18 feet, from an elevation on the pier of the same (18 feet).
Assuming $e=20^{\circ }$ as before, we have from the equation
$\mathrm {V} ^{2}={\frac {a^{2}g}{2\cos ^{2}e\left(b+a\tan e\right)}}$,
the velocity of projection of this vase,
$\mathrm {V} =21.23{\mbox{ feet per second,}}$
which is about 8 1/4 feet per second in excess of that of the wave of shock, the difference being due to the angular velocity of elasticity acquired by the pier itself, added to that of the wave. In fact, in such examples, the body thrown is projected like a stone from a sling.
There was every reason for my believing that the vase remained where I found it, half embedded in a flower-border, in the locked-up garden of the prior, and untouched since the earthquake; and the splintered and disjointed state of the limestone blocks of the pier, itself indicated the extent to which it had vibrated. The corresponding vase was not thrown though loosened, nor was the pier as much shattered, though I could not discover any very certain cause for the difference in effect upon both. Each vase had been steadied when in place by a slender iron dowal.
​I have stated that there was evidence of a third shock, different in direction from either of those already considered. This was visible in many small objects, which gave indications of disturbance, by the main shock or by the transverse one, and also of immediately subsequent disturbance, by another, or by several other minute vibrations or little shocks, in directions from south to north, varying 10° to 15° to the east or west of that. This last shock, or jarring succession of shocks, appears to have been a true earthquake echo, or reflection of the main shocks back, from the limestone mountains to the S., S. W., and S. E. of the Certosa.
In the line of buildings to the east side of the great front entrance square, between B and B (Figs. 1 and 2, Diagram No. 240) a great number of pyramidal brick chimney caps were thrown off from the tops of the stalks, in a general direction to the S. E. The mean direction of their throw I found to be 136° E. of north, which is one not so widely different from that of the resultant path of projection due to the two main shocks, but that all of these might have been projected off at the same moment and by these shocks; the differences in direction being due to the irregular figure of the pyramids, and to their ordinal position with reference to the resultant path, as well as to their having in some cases probably slided after their fall upon the sloping tiling of the roofs. The position of several of these caps, however, and the wide diversity from the resultant path of others, caused me to conclude that several of them had been loosened by the main shocks, and afterwards overthrown by this third movement in reverse.
To the same repetition of movements I attributed the ​singular displacement of the limestone statue of the Madonna (Photog. No. 228 (Coll. Roy. Soc.) and Fig. 3, Diagram No. 240), which I found had moved upon its pedestal, without injury or overthrow, about 1 3/4 inch in a direction 115° E. of north towards the S. E. Its base was an irregular octagon. The figure had been twisted a little in a direction from north towards east, or with the hands of a watch; and its displacement appeared to have arisen, from its having rocked like a conical pendulum, round the successive sides and angles of its octagon pedestal, which the base of the figure overhung: by the conjoint influence, of the intersecting shocks, and the centre of gravity of the figure being not over the centre of the base, but nearer to the S. E. side (at which the infant rests in the Madonna's arms), the circle of gyration tended to this side, and as the figure passed round each angle at that side of the pedestal, it gained a little ground towards the direction in which I found it had shifted. The friction between the pedestal and base, there being no cement and both smooth, being small, it would be possible for a figure of this sort, however, to shift its position by merely rocking to and fro in one plane at first, the lower part shifting forward at each return oscillation, by the existence of a centre of "spontaneous rotation" between the centre of gravity and base; and such may have happened here, complicated by the two nearly concurrent intersecting shocks. The centre of gravity appeared to the eye, to be at about 2 feet 2 inches above the base, and the weight of the statue was about 3 cantari, or 6 1/2 to 7 cwt., but I had no means of further examination. The Priure, and still more the Vicario, Il Padre Bruno Santullo, were enabled to give me an intelligent and consistent account, of their experience ​and observations during the earthquake. They, and all with whom I conversed in the monastery, described the noise as being heard at the same moment, as the first movement of shock; some thought a very little before, some an instant after, and that it continued as an awful rumbling roar during the whole time of motion, and even after it. They could give but a very confused account of the second shock, which arrived about an hour after the previous ones; saying that they were all in too much alarm, and dread of the buildings around them, that were momentarily giving signs of falling, to be prepared to remark much about the last shock, except that it further ruined and shook down many things that the preceding ones had left. They had all taken refuge in the centre of the great open court, and remained exposed to the cold for several hours, before they durst return to their shattered cells.
They were unable to give any precise information as to the moment of occurrence of the first shock; and as to direction, they could only say they were shaken in every direction, and that the shocks were at first, they thought, from north or N. E., and then in every way or vorticoso. The only watch in the monastery, was a curious old English one, the maker's name and date in which proved it to have been made about 140 years before; and with a singular notation for the hours upon the dial, which the owner had never been able to make out until I deciphered it for him. It may therefore be imagined that it was not kept very exact as to time, and probably had not for a hundred years shown true time, until the day when I set it at noon, for the venerable and simple-hearted owner.