BC=r, the radius where the horizontal force is a maximum The angle CAC' is therefore very nearly 70° 31' 43", which is the angle of the cone whose base in the horizontal plane limits the zone of maximum disturbance; and as the angles at B are right, the angle of emergence BCA=54° 44′ 9", and the sides of the triangle, BC: BA: AC, are to each other in the ratios of 1:2:√3. Hence we arrive at the very simple practical rule. Having found the coseismal zone of maximum disturbance by observation, or three points in it, and the centre of the circle passing through them, the depth below the surface, of the origin or centre of impulse, will be the diagonal of the square whose side is equal to the radius of the given circle. Within certain approximate limits, then, the application of this rule is capable of giving some information upon that great object of research, to which, above all others, seismological investigation points, namely, the depth beneath our surface from which such impulses reach us, and, by consequence, that at which active volcanic forces are in operation within our planet. This method can scarcely be applied in very mountainous regions, unless both mountain-formations and seismic energy be developed upon a grand scale, as in Mexico and South America; and in every case the observer will find himself encumbered and perplexed by the interference of many minor circumstances of disturbance to mask and render difficult his observations. These, however, should not prevent our bearing the method in mind whenever favourable conditions present themselves for its use. In the present state of the theory of wave-movements in elastic solids, it cannot be said to be experimentally certain, that the energy of the wave, in the normal, does diminish with the square of the distance. Another view of the primary conditions of its motion would make it diminish directly as the distance, in which case it may be proved that the angle CAC of the coseismal cone of maximum disturbance will be 90° and constant, and hence that the depth of the origin (upon that hypothesis) will be always equal to the radius of the circle of maximum disturbance. It would be out of place here to enter further into the physical discussion of this question, except by referring to Herschel (art. "Light," Encyc. Metrop.' vol. iv. paragr. 18. p. 578) and to the various papers of Cauchy, Wertheim, Stokes, Airy, Haughton, and Maxwell on the subject. I have stated that in the preceding investigation the effects of the transversal wave are neglected. In the observation of actual earthquake phenomena, this may probably be safely done as respects all points that are at considerable distances from the centre of disturbance. The normal and transversal waves, starting at the same instant, appear to travel with unequal velocities. They part company; and their distance becomes greater, and the interval larger between their arrivals, the further they have both travelled. Were we enabled, therefore, to ascertain the precise velocity of the normal wave, and the exact interval of time between the arrival at a distant point of the normal and transversal waves, we could still by another method arrive at the distance from which they had come, and therefore at the depth of the origin of impulse, if the angle of emergence at one point were known. According to Cauchy, the velocity of transit of the normal is to that of the transversal wave as 3:1 in media of unlimited mass; and Wertheim's modified formulæ for elastic bodies fix it as 2:1. My own experimental observations with the seismoscope have proved to me that the separation of the two waves can be noticed, and the interval of time measured upon even very moderate ranges of wave-transit, not exceeding a few miles; and the observations of earthquake shocks indicate that one cause of the tremors that usually succeed L the main blow, is the later arrival of the normal wave, whose amplitude at Frans vers considerable distances from the origin is always small. However this may be, it is certain that in all earthquakes the real mischief and overthrow, at places pretty far removed from above the centre of impulse, are done by the blow from the normal wave, which appears to come first; hence the main observable effects are those of the normal, and we are justified and enabled, in such localities, to neglect the transversal. But within a considerable circle of area, whose boundary is evanescent, and whose centre lies at the point B (figs. 7, 8), right above the origin, the actual effects of the transversal wave are very formidable, and can never be neglected. The ground beneath an object so situated, such as a house or pillar (as the distance from the origin to the surface is the minimum range of emergence, or shortest possible, and therefore its energy the greatest), is almost at the same instant thrown nearly vertically upwards by the normal wave, and at the same moment rapidly forced forwards and backwards horizontally in two directions orthogonal to each other; and this combined movement, which is that called "vorticoso" by the Italians and Spanish Mexicans, is one that nothing, however solid and substantial in masonry, &c., can long withstand. Hence it follows that, within the zone of maximum disturbance which we have treated of, and occupying its central region, we shall always find an area, more or less circular, also of great overthrow and destruction, though presenting entirely different characteristics as to the manner of overthrow of the buildings, &c. This middle region may therefore be sought for as a further directrix to the point B over the centre of impulse. It may be necessary to remark that this combined movement, due to the two transversal waves, and limited to a region closely above the prime vertical passing through the centre of impulse, must not be confounded by any misconcep tion of the phrase "vorticoso," with that false notion of vorticose shock, such as was presumed to have twisted the Calabrian obelisks, &c., the real nature of whose displacement I indicated in 1846. (Trans. Roy. I. Acad. vol. xxi. part 1. See also 1st Report Trans. Brit. Assoc. 1850, pp. 33, 34.) In conclusion, I would repeat my conviction that a further expenditure of labour in earthquake catalogues of the character hitherto compiled, and alone possible from the data to have been compiled, is now a waste of scientific time and labour. The main work presented for seismologists in the immediate future, must consist in good observations, with seismometers advantageously placed at sufficiently distant stations, and galvanically connected as to time; and in the careful observation of the traces left by great shocks (when of recent occurrence) upon buildings and other objects artificial and natural, with a view to determining the nature of the forces that have affected them, aided by the resources of the physicist and mathematician. Amongst the unknown regions of our world, as respects the recurrence of earthquakes and their phenomena, the most prominent are Central Africa, Abyssinia, Madagascar, Northern Asia, and the north-west of North America. For observations of the last, the new settlements about being formed at Vancouver's Island will, no doubt, offer great facilities, as well as future access to the great Aleutian chain of volcanoes and their seismic zone. I reserve for the Appendix a few observations, upon great sea waves and certain ill-understood phenomena, which could not systematically find place in this Report. APPENDIX. No. I. (P. 48.) The following table of some of the men and events upon which the progress of human knowledge and discovery and the diffusion of mankind have depended, may serve to illustrate the relations that these bear to the expanding character of the catalogue : Amber and tin carried by Phœnicians from the Baltic and England to the Levant.. 600 eclipses calculated.-Pythagoras 500 Trireme galleys in use. The burning-lens known 400 300 Clepsydra. Balliste. Silver coin at Rome. The olive. - Chinese wall. -Hannibal 200 year fixed... 100 Christ born. - Seneca. -Strabo. First sea voyage to India, probably The Western Empire.-Public lights at Antioch.-Church bells The dark ages commence. Franks Christianized. Silk-worms in Europe... Hops. Quill pens.-Latin disused. - Mahomet I. A.D. 3 Stained-glass windows the vine-Saw-mills-Monachism all in Germany 300 400 500 600 Charlemagne names the days and months 800 Date A.D. Oxford and Cambridge Universities. - First book.-Alfred the Great 900 1100 of London. The Popish inquisition.-Saladin 1200 English parliaments. - English in our law courts. Gunpowder.---Cannon. Mariners' compass.-Printing. - Engraving. Oil painting. -Coaches. Roger Bacon. -Wiclif. Tamerlane 1400 America. Columbus's four voyages, from 1492 1504.-Cape of Good Hope.Indian Sea. Vasco di Gama, 1499.-John and Sebastian Cabot, 1497.-Public road and bridges through Western and Southern Europe.--- Luther. The Reformation 1500 Logarithms. Watches. - Barometer. - Telescope. Mercator. - Italian book-keep ing.-Jupiter's satellites discovered. - Copernicus. Galileo. Magelhaen's voyage, 1520.-Drake's voyage, 1580 1600 Royal Society. - Newton. - Sextant. - Chronometers. - Greenwich Observatory. Tea into Europe. - Clive. - Penn. South Sea Company. - Cod and herring fisheries. Semaphore.-New style calendar. Anson's voyage (1744) Cook's last voyage (1779) 1700 La Perouse (1788) Vancouver (1795) Watt's steam engine (1796) Napoleon. Nelson. Embassies to China and Japan. --Vaccination. -Gas lights. -Life-boats. - Public docks. - Public coaches and diligences. Newspapers abundant 1800 to Steam navigation. First steam-ship 'Savana' crosses the Atlantic, 1819. - Rail- (present way system, 1820.- Electric telegraph, 1830. - Law of tides-of storms. date. Gold in California-in Australia No. II. (P. 57.) From the interest that belongs to observations of earthquakes in the Southern Hemisphere, hitherto so seldom recorded, I append the following extracts from the letter of an intelligent friend, referring to the New Zealand shock of 1854-55, written very soon after the event. The writer is a civil engineer. The New Zealand Earthquake. "Wellington, 23rd January, 1855. "Whilst sitting reading and talking at 8.50 г.м., I felt the house (which had been shaking with the occasional N.E. gusts so usual at Wellington) give a very extraordinary shake, which seemed to continue, and was accompanied by a fearful noise. I at once jumped up, rushed, as well as the violent motion would permit me. into the front garden, the motion increasing in violence, accompanied by a roaring as if a large number of cannon were being fired near together, and by a great dust caused by the falling chimneys. The motion at first was a sharp jerk back and forwards in a N.F. and S.W. direction, increasing in extent and rapidity, until I got into the garden-say 25 seconds; it was then succeeded by a shorter and quicker motion at right angles, for nearly the same time, still increasing, but appearing to be perfectly in the plane of the horizon. This was followed by a continuation of both, a sort of vorticose motion, exactly like the motion felt in an ill-adjusted railway carriage on a badly-laid railway at a very high speed, where one is swayed rapidly from side to side. This was accompanied by a sensible elevatory impulse; it gradually subsided; and the above, constituting the first and greatest shock, lasted altogether, I should say, 1' 20' or 1 at Wellington. The earth continued to vibrate all night like the panting of a tired horse, with occasional shocks of some violence, decreasing in frequency and violence towards morning, and nearly all in the N.E. S.W. direction, some of them a single jerk back and forwards like that of one railway carriage touching another, but generally they were followed by a vibration gradually decreasing. These lasted, with increasing intervals, until I left Wellington on the 11th April. For the first week after the first shock, the vibration never wholly ceased. All the brick buildings in Wellington were overthrown, or so injured, as to necessitate their removal; the Hutt Bridge was thrown down; the hill-sides opposite Wellington were very much shaken, as evidenced by the many bare patches with which they were chequered fully to the extent of one-third of their surface, whence trees had been shaken off: this range, particularly its lower portion, appeared to have been the most shaken. It is called the Rimatuka Range, and divides Port Nicholson and the basin of the Hutt from the Warumrapa Valley, where the earthquake was felt with greater violence than at Wellington, the ground having opened in many places 8 or 9 feet, and sunk in one place for 300 yards square to a depth of 8 or 9 feet. The cracks are very frequent, and at first were of considerable depth (de (deemed unfathomable, because people could not see their depth), perhaps 15 or 20 feet in depth, and extending for many hundred yards. Ploughed ground and mud, dry river- or pond-beds were thrown up into all sorts of undulations like a short cross sea, the ridges in some cases 2 feet in he height, the prevailing direction of cracks and ridges being generally at right angles to the apparent line of force, N.E. S.W. The strata about Wellington and the Rimatuka are a sort of shale and clayslate, all broken into pieces not bigger than road-metal, with yellow clay joints; and in places where the overlying clay has been cut through by roads, one can see the cracks caused by former earthquakes filled up by a different-coloured material. I should mention the great sea-wave which came in immediately after the first shock, about 5 feet higher than the highest tide inside the harbour, and 12 feet higher outside; the tide (i. e. water-surface) continued ebbing and flowing every 20 minutes during the night, and was most irregular for a week, ebbing further than ever known before. After that time it became more regular; and now the ebb and flow is the same as before the earthquake; but since that, it does not come at high-water within 3 or 4 feet of its former height, proving that the whole southern part of the northern island has been raised, the elevated portion commencing at Wangarner, on the west coast, and going round to Castle Point on the east, where it terminates. The vertical elevation is greatest at the Rimatuka Range, outside Port Nicholson, and becomes nil at the above-mentioned points. The shock was felt at Nelson almost as badly as at Wellington, slightly at Canterbury and Ahurii. It was most violent on the sides of hills at those places, and least so in the centre of the alluvial plains. "The great shock continued at any one point longer, the further it had diverged from its apparent centre of action opposite Wellington, and became less violent, the motion being slower and not to such an extent. This I think plainly proves (if any thing were wanting to prove) Mr. Mallet's wave theory: any person of the slightest perception experiencing the shock and comparing the statements of persons who had felt it in different places could come to no other conclusion. I do not think the thermometer or barometer was affected; I had no opportunity of observing myself; but so I heard; nor was the compass acted on more than was due to the motion. "The captain of the vessel I went in to Ahurii was outside Port Nicholson, lying-to in a gale, and thought his vessel had struck, and was dragging over a reef of rocks; the next morning he passed hundreds of dead fish all of one sort, a species of ling, whose habit it is to lie on the bottom. The shock was also felt by the Josephine Willis,' 150 miles off the coast. I only regret, time and want of means prevented my making more accurate observations, and even giving you those I did make in greater detail. W. C. B." [The direction of primary shock mentioned by the writer is in the line of the mountainchain, reaching from the interior down to Wellington, and also in that pointing to Tonguro and other volcanic cones.-R.M.] No. III. BIBLIOGRAPHY OF EARTHQUAKES. At the period of publication of the Second Report on Earthquakes, it was my intention to have prepared a complete Bibliography of Earthquakes, the want of some such index having been much felt by myself, at former periods. Subsequently, however, I found that my friend, Professor Perrey, of Dijon, had had such a work in progress for some years; and he has since published his Bibliographical Catalogues in the 'Mémoires de l'Académie Imp. de Dijon,' vols. xiv. and xv. 2nd ser., for 1855-56, which contained, in alphabetical order, one thousand eight hundred and thirty-seven different works on Seismology. Even yet, however, the store of literature in this speciality are not completely taken stock of. I have hence deemed it best simply to publish, in the following lists, such works as I have found in the several European libraries named at the head of each separate list, along with one in which works, that from various sources have met my eye, are collected. The materials thus given will be, I should hope, of some present service to scientific |