Upper and Lower Wind Currents over the
Torrid Zone.

AFTER my arrival in China in 1883, I made inquiries, among persons who had kept meteorological registers, concerning the direction from which clouds usually come here, but was told that they came from all directions without any apparent order. But the observations made during January 1884, printed in the Weather Report published on February 11, showed at once clearly that the lower clouds came from the east, and that the directions veered with increasing height, the highest clouds coming from the west, as explained in the text of the Annual Weather Report published on February 17, 1885. This might have been expected in analogy with what obtains in cyclones, as the trade-wind blows into the calm belt as if this were the centre of a depression drawn out to extend round the whole earth near the equator.

The Hon. R. Abercromby, to whom my Reports were sent without delay, convinced himself of the truth of those remarks during a tour round the world, and addressed a letter to NATURE on the subject on October 26, 1885, but it is of importance that the subject should be investigated at fixed observatories within the tropics, where hardly enough attention has hitherto been paid to the movements of clouds, to judge from what has hitherto been published.

In the Annual Weather Report for 1885, it is stated that, from June to September inclusive, cirri come from two different directions-from about north-east while a typhoon is in existence somewhere, their direction often backing from about east to north while the centre of the typhoon is yet over 700 miles away; and from about west when there are no signs of a typhoon. But cirri are rarely seen in summer except before typhoons, through whose agency vapour is evidently carried up to the higher regions of the atmosphere. It is, however, to be expected that the existence of the southerly monsoon (caused by the low barometer in the northern part of the Chinese Empire) during the summer to some extent influences the movements of the clouds.

The following table exhibits from four years' observations (1884 to 1887 inclusive) the average directions from which the wind comes at the Observatory, about 150 feet above M. S. L., and at the Peak about 1850 feet above M. S. L., as well as the average directions from which the upper and lower clouds come, but the difference between the latter is so great that intermediate directions will be missed :

If an observer outside the earth were to determine the period of this planet's rotation by observing spots formed by clouds, he would obtain different values according to the level of the respective cloud-layer, just as we obtain different values for the period of rotation of Jupiter from observations of different classes of spots. In the case of the earth, the observation of the highest clouds near the equator might possibly furnish a value of the period too short by a tenth, and there is no doubt it would be different nearer the Poles. W. DOBERCK.

Hong Kong Observatory, August 11.

The Natural History of the Roman Numerals. SOME time ago I had the pleasure of reading in your journal (vol. xxxvi. p. 555) an interesting article by Mr. Lymburn on the above subject. In this the writer shows the probable evolution of the Xten, from the V hand, and thence the broad arrow, . As the Scandinavians used this arrow sign, calling it tir or tyr, as an equivalent for T in the Runes (see Taylor, "The Alphabet," vol. ii., p. 18), it is therefore connected with the Greek tau, the headless cross, the X of the Semitic languages. I have no doubt that many of your readers take an interest in anything bearing on this subject. This is my apology for calling their attention to an article published in the last volume of Transactions of the New Zealand Institute,1 wherein I break new ground by showing that the word tau was known in Polynesia as a cross, as ten, and probably as meaning "writing."

I have given, in the different dialects of New Zealand, Samoa, Tonga, Hawaii, &c., the meanings of the word, and shown its entry into other compound words. A brief précis runs as

follows:-

Tatau (ta-tau) is the Tahitian word which Cook brought to us, and is better rendered by his spelling tattow than by our English tattoo. In Maori, tatau means to count, to repeat one by one; but in Hawaiian it means to write, to make letters upon, to print as upon tapa (native cloth) as in former times. In this Hawaiian, tau means to dot, to fix the boundaries of a land or country, to give publicity to a thing. In Tahitian, tatau means not only to tattoo, but to count, number; in Samoan, tau is to count, and in Marquesan, tatau to reckon. In composition, too, it enters into many words, such as teacher, pupil, genealogy, &c., and it seems impossible but that the tattooing (at one time done in "three-marks" and arrow-heads) meant some kind of character or script.

As to the numeral "ten," I bring some interesting evidence which I cannot condense.

As to the figure of the cross being used as a sacred sign, there are innumerable evidences to that effect in the Polynesian islands; notably that the Southern Cross is called in Tahitian tau-ha ("four-cross "), and that the cross X was the taboo sign in front of Hawaiian temples. I have since learnt that in the Solomon Islands the cross taboos anything to the chief. EDW. TREGEAR.

Wellington, N.Z., August 5.

Indian Life Statistics.

THOUGH Several weeks have now elapsed since Dr. Hyde Clarke's inquiry about the effects of lucky and unlucky times and seasons upon the Indian birth-rate was published (in NATURE of July 26, p. 297), none of your readers in England who happen to be acquainted with India have come forward to answer it. I therefore write to point out that, though the times of Hindu marriages are to a very great extent controlled by supposed lucky or unlucky days, months, or years, these have nothing whatever to do with variations in the birth-rate, for the usual age of marriage of girls is from eight to ten years, and child-bearing at the earliest does not commence before twelve or thirteen.

With regard to the Holi and other religious festivals, I have it on the authority of Mr. J. C. Nesfield, Inspector of Schools in Oudh, who has made a life-long study of Hindu castes and their customs, that, whatever the origin and primary significance of the Holi may have been, it is not now connected in any The special manner with the multiplication of the species. religious ceremony to which the Hindu looks for the furtherance of his desire for offspring is the Durga Pujah, or worship of the consort of Shiva, which is the occasion of the annual family reunion all over Bengal. In the Upper Provinces a totally different festival is celebrated at the same time of the year-the Ram Lila, a sort of dramatic performance or mystery-play, commemorating the expedition of Rama to Ceylon for the recovery of his lost wife; but Mr. Nesfield says that during the Ram Lila some member of every family is specially set apart to conduct a ceremonial worship of Kali, or Durga, ending with the sacrifice of a male kid, and that the object of this ceremony is to obtain the favour of Kāli and her consort for the continu

I Trans. N.Z. Inst., vol. xx., “Ancient Alphabets in Polynesia," by E Tregear, F.R.G.S. (London: Träbner and Co.)

I

CAN any of your readers help me in the following case? am a shell-collector, and my minute and delicate species (Dip lommatina and such like) are kept in glass tubes. i have lately observed that some of the tubes in the cabinets were becoming opaque; a milky efflorescence seemed clouding the inside surface. I found the same thing in a box containing about 100 that I had placed on one side. I then opened a box of 500 which had never been unpacked since they were received, some four years ago. All these are more or less affected! I then opened a third box, from another maker, and in this 500 I observed many beginning to be affected. What can be the reason? Each of these tubes is tightly corked, and I see the glass under the cork is not affected. I have tried various means to restore the clearness without avail. I have boiled some, and roasted some in the sun, steeped others in alcohol, oil, &c.; nothing seems to do any good. Can any of your scientific readers divine the cause, and suggest a remedy? E. L. LAYARD. British Consulate, Noumea.

"Fauna and Flora of the Lesser Antilles."

IN the article on this subject in NATURE of August 16 (p. 371), it is stated that Guilding discovered a Peripatus in Dominica many years ago. This is, I believe, an error, for Guilding's Peripatus juliforme was found by him in St. Vincent, an island to the south of Dominica, and the first specimen of Feripatus found in this island was, I understand, the one now in the British Museum, taken home by Mr. G. Angas.

The rediscovery of the Dominica Peripatus is rather curious. In 1883-84, at the special request of Prof. Moseley, I searched for the animal in all likely places, but did not succeed in finding any specimens. At that time Prof. Moseley and I were not aware of Mr. Angas's discovery. I mentioned my non-success to Mr. Ramage, and asked him to look out for the interesting animal, and, strange to say, soon afterwards his boy brought him three specimens, but Mr. Ramage has not been able to obtain any more. I employed the same boy after Mr. Ramage had left Laudat, and he brought me two specimens, and said that he could find no more although he had searched for several days. These two I sent to Prof. Moseley at Oxford. A few weeks ago another specimen was brought to me from the windward (or eastern) side of the island by the same boy, who found it about 300 feet above the sea, not far from the coast. Laudat is on the leeward side, at an elevation of about 2000 feet above the sea, and on the margin of the virgin forest. The six specimens of the Dominica Peripatus recently found may not belong to a new species, but the rarity of the animal is interesting. Had it been common in any degree, Mr. Ramage and I must have found it, but neither of us has succeeded in doing so.

Mr. Ramage, who has been labouring with unflagging zeal, leaves to-day for St. Lucia, but he will return here later on in the year, so as to continue his botanical work. His specimens of the forest flora form, I believe, the most complete collection that has yet been made in the island, and his enthusiastic work deserves recognition. H. A. ALFORD NICHOLLS. Dominica, West Indies, September 15.

Sun Columns.

WITH reference to the simultaneous appearance of five sun columns described by Mr. Brauner (August 30, p. 414), the following descriptions of three different manifestations of the phenomenon may perhaps be of interest.

April 19, 1887, 7.25 to 7.37 p.m., calm, sky clear except a smoky grayish haze low on the western horizon, behind which the sun had set. The solar rays concentrated into one perpendicular continuous beam of uniform diameter with the sun, and reaching to an altitude of about 20°. The beam sharply define, and of a reddish tint strong enough to be detected

behind the haze. Near the summit a few tinted strips of fine cloud forming an angle, and giving the whole the appearance, as described by the person who called my attention to it, of ship's mast and yards." No trace of side rays visible.

ני

June 10, 1888, 8 to 8.25 p.m., sun set below horizon; to an altitude of about 10°, sky comparatively clear, only a little cirrostratus; above this, to an altitude of 20°, the cirro-stratus much more dense, and in this part only was a sun column distinctly visible, terminating abruptly, and showing no trace in the cirrocumulus above. In the lower 10° there was also no evidence of changed to a deeper red by 8.15 p.m., when the clouds on both the column. It was at first of an old gold colour, then gradually sides were suffused with the same tint, and by 8.27 it had disappeared.

These two cases I observed from my own residence; the third has been communicated to me by Mr. W. Manning, who was chief officer of the ship Balmore when he witnessed the phenomenon. Not having access to the ship's log, he could not give me the exact date and position, but it was some four or five years ago, "in about 25° or 30° S. lat., and from 120° to 130° W. long., during the first dog watch (4 to 6 p.m.), observed the sun at an altitude of about 25° of a dull red colour, with all its rays apparently drawn together and forming a pillar of light reaching from the sun down to the horizon, and about the sun's diameter in breadth." Mr. Manning told me that of all the curious sights he had seen at sea none had been so impressed on his mind as this sun pillar.

These are instances of continuous pillars from the sun upwards and downwards, one showing the half furthest from the sun only. HY. HARRIES.

Rosebank, Hounslow, September 28.

THE REPORT OF THE KRAKATÃO COMMITTEE OF THE ROYAL SOCIETY1 II.

AN appendix to Prof. Judd's section on the geological aspects of the eruption embraces a series of data collected by Dr. Meldrum, F.R.S., of Mauritius, regarding the falls of dust and the occurrence of masses of pumice throughout the Indian Ocean in 1883-84, which he had already communicated to the British Association in 1885. Mr. Scott's prefatory note thereon shows that while such data are of value in exhibiting the immense magnitude of the eruption they cannot help to throw much fresh light upon the question of the Indian superficial oceanic circulation, since the pumice was evidently affected almost as Thus, while a comparison of the two maps reveals a general much by the motion of the air as by that of the water. westerly drift in the direction of the well-known lefthanded circulatory system of the Southern Indian Ocean, a detached phalanx of pumice masses off the north-west coast of Australia in 1884 (in the second map) shows, as Mr. Scott observes, a probable drift thither "before the northwest monsoon which would prevail in those seas from November 1883 to March 1884.”

In one other point, however, apart from their general interest, these data are valuable in confirming the general westerly trend of all the ejecta at the time of the eruption -a fact whose significance becomes subsequently so marked when dealing with the spread of the optical phenomena.

In the plates of geological sections which are appended to this Part attention should be paid to (3) (4) (5) (6) of Plate 4, in which natural and artificial pumice and dust from Krakatao are compare, since they have an important bearing on Prof. Judd's conclusions.

Part II. of the Report, which deals with the air waves and sounds caused by the principal eruption of Krakatao on August 26 and 27, was prepared, under the direction of Lieut.-General Strachey, F.R.S., principally by Mr. R. H. Curtis, of the Meteorological Office.

The air-waves, as apart from actual sounds, were one of the most extraordinary features of this unique out

1 Continued from p. 542.

burst; for, while it is possible that similar waves were propagated through the atmosphere during great eruptions in former years, these appear to be the only instances recorded of anything of the kind on such a vast scale since the establishment of continuous selfrecording barometers.

That air-waves caused by the sudden expansion of the erupting gases could leave a perceptible record on all the barometer traces as far as the antipodes of Krakatao, is of itself a sufficiently remarkable fact, but that such waves could record their passage back and forwards no less than seven times, is a circumstance which even now, five years after its occurrence, fills us with astonishment. A selection of forty-seven stations has been made, which, as far as possible, represent the habitable world; and the times of passage of the wave from Krakatao to the antipodes and from the latter back to Krakatao have been deduced by comparing the significant, and in many cases similarly-shaped, notches in the barometer traces.

Of course, where, as in the present case, the form of the wave itself was complicated, gradually became deformed, and was traceable for no less than 127 hours from its commencement,perfect accuracy in determining the precise moments of passage of the various phases could scarcely be expected. Yet it is evident on the face of it that a very high degree of accuracy has been attained, by which not only can the precise moment of the great outburst be determined by the simple process of calculating backwards, but also certain variations of velocity be traced in portions of the wave which took different routes over the globe.

The general pace at which the air-wave spread outwards in concentric circles from Krakatão as a centre, was 700 miles per hour, which is slightly less than the velocity of sound at zero Fahrenheit, viz. 723 miles. The entire circuit of the globe and back was thus made in about thirty-six hours. Also, by a careful comparison of times and probable errors, the probable moment of the greatest explosion is calculated to have been 2h. 56m. G.M.T., or 9h. 58m. local time, on the morning of August 27.1

This great explosion appears to have been not only the culminating point of the Krakatao eruption (the preceding minor outbursts appearing as a mere roughening of the barometer scale, or a series of moderate oscillations on that of the gasometer at Batavia), but owing to its surpassing intensity, a feature altogether peculiar to this eruption, and one by which it will always be distinguished from others, such as that of Asama (Japan) and Skaptar Jokull in 1783, or Tamboro in 1815, which, in respect of the amount of material ejected in the form of lava, and other effects, appear to have equalled if not exceeded it. One of the most interesting results of this discussion of the Krakatao air-wave has been the discovery of its variation of speed according as it travelled with or against the earth's rotation. As a general fact it may be said that such variation is plainly traceable to the prevalent drift. of the winds.

Thus in the extra-tropics the wave moving from west to east was accelerated, and that from east to west retarded, by about 14 miles per hour; while within the tropics the wave which passed through Mauritius and Loanda was affected in a precisely reverse manner, the passage eastwards being retarded, while that westwards was comparatively unaffected, the amount corresponding to an east to west wind of about 10 miles an hour. It is at least curious to notice, that on p. 35 of the "Motions of Solids and Fluids," by Prof. Ferrel (Washington, 1882), the value of the due E. to W. component of the trades between 15° N. and S. lat. is given as 12 miles per hour, while the mean of the W. to E. component of the antitrades for latitude 45° at the earth's surface and a height of 3 miles above it, is exactly 141⁄2 miles per hour.

This differs by only 4 minutes from 10h. 2m., the epoch determined from fewer data by M. Verbeek.

The greatest general retardation took place in the Southern Ocean, possibly owing to the low temperature of the southern hemisphere in August. All these points are very distinctly shown in the diagrams.

As regards the actual sounds, the facts are without precedent. The unvarnished record reads like a fairy tale. When we are told that at distances of over 2000 miles from the volcano, the noise was like the firing of heavy guns, and that at numerous points of the Indian Ocean steamers were despatched in search of supposed vessels in distress, we are prepared to accept with less hestitation the numerous other collateral evidences of the enormous explosive energy which generated them.

The area over which the sounds were heard is roughly estimated at one-thirteenth of the entire surface of the globe. In other words, it was nearly equal to Europe and Africa together, or slightly exceeded that of both Americas. All these details are illustrated by numerous diagrams.

Part III., by Captain W. J. L. Wharton, R.N., F.R.S., deals with the so-called seismic sea waves generated during the eruption; one of which not only dealt death and destruction all over the Straits of Sunda, but travelled as far as Cape Horn, and possibly the English Channel.

It appears that there were two sorts of waves generated -one of long period (two hours), which alone recorded itself on the automatic gauges and travelled to great distances; and others of much shorter period, which were mostly confined to the immediate vicinity of the volcano.

The only hypothesis by which the facts can be reconciled, according to Captain Wharton, is that at the time of the greatest explosion, at 10 o'clock on August 27,"waves of both characters would be more or less synchronously formed," the longer wave being caused by upheaval, and the shorter ones, which caused the destructive effects in the Straits of Sunda, by the displacement due to ejected masses or fragments of the volcano falling into the sea all round it.

In proof of upheaval, which appears to be the only probable cause of the longer wave, Captain Wharton cites the generally shallowed condition of the sea immediately surrounding Krakatao, especially on the northern side.

We cannot, however, help observing that, according to Prof. Judd, the geological evidence is entirely against upheaval throughout the area; and the formation of the new shoals and islands is attributed by him solely to the piling up on the sea floor of the coarser matter, including the framework of the volcano, which was ejected during the explosive outbursts. It is a remarkable fact, indeed, that during the eruption there was no trace of any local seismic disturbance such as might be supposed to accompany an upheaval of the ground. A variety of peculiar effects were witnessed, such as clocks stopped, lamps broken, and houses cracked, but all of these were traceable to air and not earth vibrations.

The precise cause, therefore, of the long wave will, as Captain Wharton says, "ever remain to a great extent uncertain." One fact, however, remains clear-that both it and its minor predecessors were distinctly connected with corresponding explosions from the crater, which recorded themselves in unmistakable language on the gasometer pressure-gauge at Batavia. Whatever the precise proximate cause, therefore-whether slow upheaval, according to Captain Wharton, or the impact of falling matter, according to Prof. Judd-the action commenced with each explosion. The height of the local manifestation of the great wave at 10 o'clock is estimated to have been 50 feet, though in places where it reached the shore it appears to have run up to 70 feet.

The terribly destructive effects of these shorter "superseismic" waves, of which this one appears to have been the greatest, are amply detailed in M. Verbeek's Report, and the accompanying views of the localities visited. They reached the above majestic height only in the

immediate vicinity of the volcano, rapidly falling off in size at a comparatively short distance from the Sunda Straits.

The longer waves, with the original period of two hours, are traced by automatic and eye observations to have proceeded mainly in a westerly direction from Krakatão, being noticeable at Ceylon, all over the western part of the Indian Ocean, the south coasts of Africa and South America, the west coast of Australia, and possibly-though the evidence is not free from doubt-as far as the west coast of France and the entrance to the English Channel. In other directions, such as the China Sea, the Pacific, and the Gulf of Mexico, they do not seem to have been felt, the supposed indications not being compatible in any way with the times and distances.

=

As a general result, it may be said that the mean depths deduced by the formula V gh, from the best data for the speed of the waves, corresponded fairly with that given by the soundings, but in nearly every case the formula gave a smaller depth than the soundings. This and other circumstances lead us to conclude, not so much that the formula is incorrect, but that, with so few, and in some cases such badly placed, automatic gauges, and from such complex oscillations as seem to have occurred in many of those discussed in this section, it is scarcely possible to arrive at anything but a very rough approximation to the mean depths. The shelving of the bottom near land, which in many cases is not well determined, and the possible existence of ridges in mid-ocean, constitute obstacles to a determination of mean depth, which is all the passage of such waves can indicate. In so far, however, as they yield an approximate check of this kind on soundings, their observation ought to be encouraged by the establishment of more automatic gauges in suitable spots.

One very peculiar feature of the Krakatao long waves is that, while their original period when leaving Krakatao was two hours, they became subdivided (possibly by an interpolated series caused by reflection from the coast of Java) into waves of half this period; and, by the time they reached the North Atlantic, into waves of about one-quarter of this period. Their consecutive oscillations could thus only be identified with those of the original oscillations by doubling or quadrupling the observed periods.

Although at great distances from Krakatao the height of the largest long wave was, as might be expected, only a few inches; at such comparatively remote places through the more open route to the west as Ceylon and Mauritius, the higher and shorter waves made their presence felt to heights of several feet, and created considerable astonishment as well as damage in these localities.

Like the air and sound waves, the occurrence of seismic waves on such a scale and over such a wide area appears to have been quite unprecedented; and their discussion, like that of the former, will in the present case probably yield results of considerable value to hydrography as well as other branches of science.

(To be continued.)

FOUNDATIONS OF CORAL REEFS.

THE HE following extract from a letter from Captain Aldrich, R.N., H.M. surveying-ship Egeria, now employed in the Pacific Ocean, is interesting from several points of view.

". . . . The following morning at daylight (July 10) we picked up 268 fathoms (volcanic rock) some considerable distance southward of the Pelorus Reef. This, again, will involve a further search. Twelves miles to the northward the depth was 444, and two subsequent soundings at fivemile intervals gave 713 (ooze) and 888 (ooze). From here the soundings continued to grow shoaler, until in lat. 22° 51' S., long. 176° 26′ W., we sounded in 335 fathoms (cinder), being close to the assigned position of the

Pelorus Reef. The water deepened again to 719 (cinder), when we hove to for the night. On July 11 we continued about this position, the shoalest sounding being 246. On the 12th we continued the search, and by following up at quarter-mile intervals struck 95 fathoms late in the afternoon. Prepared a beacon, and the following day (July 13), after excellent star observations, sounded and shoaled as yesterday, and when the men were standing by to slip the beacon, discoloured water was reported from the mast-head; it was almost immediately seen from the deck, and by 9 a.m. the beacon was dropped in 24 fathoms, with a stretch of light-greenish water extending in a northerly and southerly direction for about half a mile. The whalers were lowered, and remained all day in this green water.

66

Meantime more discoloured water was reported from aloft, and I sent Mr. Kiddle up with his glasses, and he verified the report; so, leaving the boats on the Pelorus, I went with the ship, and, after going two miles, I made out the small streak from the poop. It had remained as steady as possible, and had every appearance of being a very small shoal. The ship was taken to within 100 yards of it, and the dingy lowered to get a sounding on it; no bottom, however, could be got, so the ship was put in the middle of it and a sounding of 150 (no bottom) obtained. A bucket of this water was drawn and a bottle of it preserved, but I do not see anything in it to account for the light greenish colour, and it may be that the colouring matter may not lie actually on the surface; the fact remains, that this small patch was sighted at very nearly three miles distance from aloft, and that even when within 100 yards of it I believed it to be shoal-water, and that a sounding of 150 (no bottom) was actually obtained in the middle of it. On our return to the Pelorus, I was not, therefore, much astonished when I found that no very shoal water had been got by the boats. The ship was anchored in 14 fathoms, not far from the beacon, and the wire machines put into the whalers, and a search on bearings from the standard compass and mast-head angles carried on during the afternoon and on the next day, July 14. Nothing less than 14, however, was got, and I am under the impression that nothing less is to be met with, as the bottoms are loose ashes and cinder; so that, as in the case of the Graham Shoal, there may have been a shoal quite recently which does not exist now. I think that had there been anything dangerous about it we should have seen it, as anchoring in 14 fathoms mid-ocean caused many inquiring eyes to be cast around. . . .

"Another curious thing about the greenish water is that I went over it all in the ship; and the line between it and the dark water was most distinct. Moreover, the shoalest sounding of 14 fathoms was not found in the light water, but in the dark water alongside it. There was no sign of coral among the bottoms brought up. . . . My attention was pretty well occupied at this time, and it did not occur to me to do more than have a bucket of the water drawn from the green colour to preserve, which has been done. Afterwards, I much regretted that I did not get specimens from different depths, as certainly this is a from the existence of some colouring matter, not coral; most curious instance of, in one case, picking up a shoal and, in the other, of being almost positive that a shoal existed where an actual sounding proved it not to do so. I can quite excuse a man reporting a shoal under such circumstances, and it may be that a good many of the reported dangers have come on the charts in this way...”

The position of the Pelorus Reef referred to is in lat. 23° S., long. 176° 25′ W., about forty miles south of Pylstaart Island, which is volcanic. The reef was originally reported in 1861 by H.M.S. Peiorus, Commodore Seymour (now Lord Alcester), the ship passing within onethird of a mile of it, when breakers were distinctly seen.

Lord Alcester assures me that there was no doubt of the breakers, otherwise it might be thought that the deceptive appearance that misled Captain Aldrich, also misled the officers of the Pelorus.

It thus appears probable that, as in some other cases (of which the Graham Island in the Mediterranean is perhaps best known), the cinders and ashes which formed, and still form, the summit of the volcanic mound originally thrown up, are being by wave-action gradually swept away, and will continue to be so removed until the top of the bank is reduced below the limit of such action, or, as in the case of the Graham Shoal, the solid rock is laid bare.

If so, it is another case of the preparation of a suitable foundation for coral builders by a process directly the reverse of that of building up by marine organisms on mounds that have failed to reach the surface, suggested by Mr. John Murray to be the principal method.

It remains for those who have made submarine eruptions their study to say whether a mound raised in the sea is covered with loose matter in a sufficient percentage of cases to justify this mode of coral-foundation-making being given an important place amongst others.

In the latest known cases of islands so formed, viz. Steers and Calmeyer Islands, thrown up near Krakatão in 1883, and Falcon Island, which appeared in 1885 in the Tonga Group, the surface structure was loose. The two former very shortly disappeared below the level of the sea. What is happening to the latter is not known, as it is seldom sighted; but from its volume and height (290 feet) the process of reduction, even if no compact nucleus exists above water, must be slow.

The deceptive appearance of the masses of minute organisms which floated in the vicinity of the bank is no doubt an abundant source of false reports. These clouds of matter are commoner in inclosed and calmer waters, like the Red Sea, than in open oceans, where they are so much more liable to be dispersed by the waves before they can accumulate to any size. The assistance they afforded in this instance to the searchers is remarkable, and so far as I know unique, as they are generally found in deep water. W. J. L. WHARTON.

RECENT VISIT OF NATURALISTS TO THE

GALAPAGOS.

CAPTAIN J. M. DOW has placed at my disposal
the subjoined short account of a visit recently paid
to the Galapagos Group by the United States steamer
Albatross, which will, I am sure, be of much interest to
naturalists.
P. L. SCLATER.

U.S. Commission of Fish and Fisheries,
Steamer "Albatross," Acapulco, Mexico,
April 24, 1888.

CAPTAIN J. M. Dow, Panama.

MY DEAR SIR,-Thinking that you might like to know something of the results of our trip to the Galapagos, I take this opportunity of writing.

Leaving Panama on the morning of March 30, we made during that day six hauls of the trawl in depths from 7 to 51 fathoms. These gave us fine results, including many species with which you are doubtless familiar. The fishes included species of Upeneis, Arius, Polynemus, Aphronitia, Serranus, Selene, Prionotus, Hamulon, Synodus, Tetrodon, Ophidium, Sciana, Micropogon, Lophius. We were delighted to see Thalasophryne and two allied species. The number of shells, Crustacea, &c., was almost innumerable. The care of so much material kept us very busy. The next day we sounded off Cape Mala, and found the depth to be 1927 fathoms. No more dredging was done until we neared the Galapagos on,April 3, when we made a haul in 1379

fathoms, where the amount of material obtained was small, although it included some very good things. At the islands we made visits to eight of the principal ones, Most of our days were spent on shore, beginning early in the morning, and oftentimes bird-skinning and other work was prolonged far into the night. The islands presented a very inhospitable look along the shores, with the black lava cropping about everywhere; but in two of them (Chatham Island and Charles Island) the interior was extremely fertile and pleasant. Collecting was always difficult; but, with the co-operation of officers and men, we obtained a great quantity of material. We naturally looked to the birds first, on account of Darwin's previous work there. We have over 250 good bird-skins, besides several hundred specimens in alcohol, and a few skeletons. Of the fifty-seven species before reported from there, we obtained examples of fifty or more, and we have, in addition, several which are apparently new to science. We hope, with our material, to settle some of the curious problems of these islands.

We secured specimens of all the reptiles which have been before found there, and also hope that we have two or three new lizards. The tortoises excited great interest, and it would please you to see the many large ones which are now crawling about our decks. We expect now that we shall be able to raise them in the States.

Fishing was good at all of our anchorages, and we all had sport in catching fishes over the ship's side. We got between thirty and forty species in all, including a large brown "grouper," which is there caught and salted for the Ecuador market.

One night, while running from one island to another, we stopped and drifted for a while, and put the electric light over the side. Besides many small things, large sharks came around in great numbers. More than twenty were seen at once, and I know that the sight would have pleased you. We all regretted that you were not with us. Notwithstanding the necessity for rapid work, goodfellowship always prevailed as usual. I hope that some time you may take a trip with me on the Albatross, and see how we do it.

Hoping that this will not prove too long an account for you, I remain,

Yours very sincerely,

LESLIE A. LEE.

THE BRITISH ASSOCIATION,

SECTION A--MATHEMATICAL AND PHYSICAL SCIENCE.

A Simple Hypothesis for Electro-magnetic Induction of Incomplete Circuits; with Consequent Equations of Electric Motion in Fixed Homogeneous or Heterogeneous Solid Matter, by Sir William Thomson.

(1) To avoid mathematical formulas till needed for calculation consider three cases of liquid motion which for brevity I call Primary, Secondary, Tertiary, defined as follows:-Half the velocity in the Secondary agrees numerically and directionally with the magnitude and axis of the molecular spin at the corresponding point of the Primary; or (short, but complete, statement) the half velocity in the Secondary is the spin in the Primary, and (similarly) half the velocity in the Tertiary is the spin in the Secondary.

(2) In the Secondary and Tertiary the motion is essentially without change of density, and in each of them we naturally, therefore, take an incompressible fluid as the substance. The motion in the Primary we arbitrarily restrict by taking its fluid also as incompressible.

(3) Helmholtz first solved the problem-Given the spin in any case of liquid motion, to find the motion. His solution consists in finding the potentials of three ideal distributions of gravitational matter having densities respectively equal to 1/4′′ of the rectangular components of the given spin; and, regarding