should never have found time and power to complete. Professor Perrey, formerly of the Faculté des Sciences of Dijon, now en retrait, who has devoted a long and useful life to assiduous labours in connection with Seismology, was our great ally; and his catalogues are so large and complete for most known parts of the world after 1842, that we were able to arrest our own catalogue at that date, and take M. Perrey's as their continuation up to 1850.

The whole British Association Catalogue thus embraces the long historic period of from 1606 B.C. of vulgar chronology, when the first known Earthquake is recorded, to A.D. 1850; and the base of induction which it presents as to the facts recorded extends to between 6,000 and 7,000 separate Earthquakes. My Fourth Report ("Reports, British Association, 1858,") is occupied principally with the discussion of this great catalogue, and with that of several special catalogues produced by other authors with limited areas or objects.

The discussion of M. Perrey's local catalogues with those of others, in reference to a supposed prevalent apparent horizontal direction of shock in certain regions—as to distribution, as to season, months, time of day or night, relation to state of tide—the bearings of the views of Zantedeschi and others as to the probable existence of a terrane tide—the supposed relations of the occurrence of Earthquakes upon the age of the moon, as deduced by Perrey, viz.: that 1st, Earthquakes occur most frequently at the syzygies; 2nd, that their frequency increases at the perigee and diminishes at the apogee; 3rd, that they are more frequent when the moon is on the meridian than when she is 90° away from it—and the views of several authorities as to the distribution of Earthquakes in time and in space—occupy the first 46 pages of this Report.

It then proceeds to discuss the distribution in time and in space as deduced from the full base of the great catalogue.

The results as to time are reduced to curves, and those as to space (or distribution over our globe's surface) to the great seismic map (Mercator's projection), upon which and in accordance with certain principles and conventional laws, which admit of the indication of both intensity and frequency, all recorded Earthquakes have been so laid down as to present a real indication of the distribution of seismic energy for the whole historic period and all over the world.

The original of this map, which also shows the Volcano (size, about 7 feet by 5 feet), remains for reference in the custody of the Royal Society. A reduced copy was published with the Report, and to a still more reduced scale has been reproduced in other places. It is impossible here to do more than refer to a few of the more salient points.

As regards distribution in time, durational seismic energy may be considered as probably constant during historic time, though it is probably a decaying energy viewed in reference to much longer periods. It does not appear of the nature of a distinctly periodic force.

1. Whilst the minimum paroxysmal interval may be a year or two, the average interval is from five to ten years of comparative repose.
2. The shorter intervals are in connection with periods of fewer Earthquakes, not always with those of least intensity, but usually so.
3. The alternations of paroxysm and of repose appear to follow no absolute law deducible from these causes.
4. Two marked periods of extreme paroxysm are observable in each century (for the last three centuries), one greater than the other—that of greatest number and intensity occurring about the middle of each century, and the other towards the end of each.

As respects season, there appear distinct indications of a maximum about the winter solstice, and equally so of a minimum rather before the autumnal equinox. It is not improbable that there is a remote relation between Earthquakes and the annual march of barometric pressure.

We may expect, at present, one great Earthquake about every eight months, and were we possessed of a sufficient report from all parts of our globe, we should probably find scarcely a day pass without a very sensible Earthquake occurring somewhere, whilst, as regards still smaller tremors, it might almost be said that our globe, as a whole, is scarcely ever free from them.

As respects the distribution of seismic energy in space of our earth's surface, it is that of bands of variable and of great breadth, with sensible seismic influence extending to from 5° to 15° transversely, which very generally follow:

1. The lines of elevated tracts which mark and divide the great oceanic or terra-oceanic basins (or saucers, as I have called them, from their shallowness in relation to surface, in this discussion) of the earth's surface.
2. And in so far as these are frequently the lines of mountain chains, and these latter those of volcanic vents, so the seismic bands are found to follow these likewise. Isolated Volcanoes are found in these bands also.
3. While sensible seismic influence is generally limited to the average width of the band, paroxysmal efforts are occasionally propagated to great distances transversely beyond that.
4. The sensible width of the band depends upon the energy developed at each point of the length, and upon the accidental geologic and topographic conditions along the same.
5. Seismic energy may become sensible at any point of the earth's surface, its efforts being, however, greater and more frequent as the great lines of elevation and of volcanic activity are approached; yet not in the inverse ratio of distance, for many of the most frequently and terribly shaken regions of the earth, as the east shore of the Adriatic, Syria, Asia Minor, Northern India, etc., are at great distances from active Volcanoes.
6. The surfaces of minimum or of no known disturbance are the central areas of great oceanic or of terra-oceanic basins or saucers, and the greater islands existing in shallow seas.

Space obliges me to pass unnoticed here many minor but not unimportant deductions. The discussions as to distribution in time and space occupy seventy-two pages of this fourth and last Report, the remainder of which (thirty-one pages) embraces the description and mathematical discussion as to seismometers, to which I may refer, as comprising the most complete account of these instruments that has, I believe, been anywhere given.

The appendix to the Report comprises the entire bibliography of Earthquakes collected during those researches, and a concluding chapter on desiderata, and inquiries as to ill-understood phenomena supposed to be connected with Earthquakes.

In 1849-50, I was honoured by the request to draw up the article "Earthquake Phenomena," which has appeared in the first and subsequent editions of the "Admiralty Manual of Scientific Inquiry." Originally the subject was intended to have formed part of the article on Geology, entrusted to Mr. Darwin, who consulted me upon the subject; and upon my representing how much Earthquakes had, within a short time, become matter for the mathematician and physicist, he, with a singleness of eye to science which it is but just to place on record, took the necessary steps with the Admiralty authorities that Earthquakes should form a separate article, and advised its being placed, as it was, in my hands. To record this will, I believe, be sufficient justification for my reference to this article, in which a good deal of information as to Seismometry is to be found.

By recurring to Mr. Hopkins's Report on Earthquake Theory, before remarked upon