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section, undoubtedly form one of the most valuable contributions in the whole inquiry. Never before has so vast an atmospheric disturbance been recorded by the barometers of the world; never, we believe we may add, have the diurnal tracings been thought of as likely to be sought for in connexion with the activity of a distant volcano. They have emerged from their quiet recesses with one accord to bear testimony to the truth of a scarcely credible tale. From forty-seven stations, fairly representing the whole civilised world, we learn that the wave spread out from Krakatoa as a centre, expanding in a circular form till half round the globe, concentrated again towards the Antipodes, whence it started afresh and travelled back to Krakatoa, occupying in the double journey thirty-six hours, rebounded, and set off again on the same revolution, and repeated the movement at least three times sufficiently strongly to be recorded. At some stations no less than seven passages, going and returning, are indicated by the diagrams. The whole process was almost exactly similar to the alternate expansions and contractions of a wave of water caused by dropping a stone at the centre of a circular pool. Certainly, without the most general and impassive testimony in its favour, the startling induction represented with calm precision in these four fascinating plates would have been contemptuously rejected. But the sensitive paper of the barograms has no theories and no prepossessions, no personal equation and no love of the marvellous, no credulity, and, above all, no incredulity. In a matter of human observation, nothing stands so much in the way of progress as the indolent habit of explaining the new and unknown by the old and familiar, the unreadiness to derive new ideas from new facts; and a quick imagination, though sometimes mistaken, proves itself more productive in the end than the mind which either rejects the fact for its novelty, or insists on saddling it uncomfortably on an old hypothesis. But the safe groundwork of facts always repays close attention. All through this inquiry we are reminded of the large results to be obtained by small but accurate instruments, and by a few careful measurements, rather than by numerous casual observations. From the barograms, then, we have tidings of atmospheric movements comparable to gigantic waves of sound, starting from a small area and encompassing the globe, not only once, but several times in succession, completing each circuit in about thirty-six hours. The mean speed of propagation was about seven hundred miles an hour, which is less, by twenty-three miles, than the

velocity of sound at zero Fahrenheit; the velocity, in fact, seems to have corresponded to that of sound in air at twenty or thirty degrees below zero. No explanation is given of this deficiency. It is believed, though perhaps not established, that the rate of propagation of sound diminishes with diminishing intensity, and since this air-wave must have become very greatly reduced in its circuit of the earth, we should find that a longer time was occupied in the second and third circuits than in the first. The diminution actually occurred; the rate for the first passage in one direction was 10-23° per hour, for the last passage 9.77° per hour, and in the other direction 10.47° to 10.27° respectively. But, considering the wave as a sonorous vibration of great intensity, it is remarkable that the rate to distances of two or three thousand miles in the tropics, where high temperature would favour rapidity of advance, did not much exceed the rate to much greater distances and to places in higher latitudes. One other factor would tend to increase velocity. Low notes. are supposed to travel faster than high notes, and this wave might be considered as of a note far below the range of hearing. Yet its maximum rate was only slightly above that of sound in air at 0° Fahrenheit.

One result revealed by the tables seems especially noteworthy, the difference of the velocities of the waves which travelled with and against the direction of the earth's rotation, amounting to about twenty-eight miles an hour: this is accounted for by the direction of the winds along the paths of the waves which passed over the majority of the stations being on the whole westerly. A current of fourteen miles an hour would, it is stated, cause a corresponding acceleration, or retardation, in the wave, according as the wave were advancing with or against it, resulting in the observed difference of twenty-eight miles. From Krakatoa to Mauritius the rate of the wave was comparatively unaffected; in the opposite direction from east to west round the earth to Loanda on the west coast of Africa it was retarded. Speaking generally, in the extra tropics the wave from west to east was accelerated, that from east to west retarded, while within the tropics the eastward passage was retarded. So far as can be gathered therefore from the data, a general movement of the air within the tropics from east to west may be inferred, and without the tropics from west to east. Those waves which passed near the north and south poles give unaccountable results, for the direct wave from Krakatoa vid the North Pole does not seem to have been sensibly

retarded by the low temperature, and the velocity of that which passed close to the South Pole was only very decidedly reduced after the first passage, and in the next circuit was greatly increased. The barometer curves of forty stations, mostly European, are given on a much reduced scale, and copies of barograms from eight selected stations show the character of the first four oscillations; elaborate tables showing the intervals between successive waves are appended.

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The pressure-gauge from the Batavia gasworks supplies an interesting narrative of the various air-waves passing over the town on August 26 and 27; this is reproduced both in M. Verbeek's and in the English Report. Very strong outbursts appear to have taken place about 5 P.M. August 26, and from midnight to 10 A.M. on the 27th, the hour of the culminating explosion which so far exceeded all the rest and drove the pencil against the stops of the scale. The differences of pressure within a short space of time exceeded 0.4 in. of mercury, if we correctly read the diagram. But the accompanying detonation does not seem to have corresponded in excessive intensity with the amplitude of the wave on which it was borne.

The immediate consequences of the great explosion were that a wave 50 feet high and of great breadth swept along the strait and with diminishing height traversed the Southern Ocean; the sea for hundreds of miles was covered with masses of pumice descended from the darkened sky, an airwave of unexampled grandeur was circling round the globe, impenetrable darkness extended for scores of miles in many directions, ashes and dust fell in great quantities on ships hundreds of miles distant, and within a circle of 2,000 miles people of many nations and languages were unsuccessfully puzzling at the riddle of strange noises. This was not all. Not only were earth and sea disturbed and the air darkened near the Sunda Strait, but on the same day the blue sky was almost covered with a thin white mantle a thousand miles and more westwards, and the sun himself was almost extinguished, struggling through the mist either like a dull red lamp or a ball of fire, or like a weak moon, or, as at Batavia, emerging from the dust-cloud transformed to green. The rapidity of these events is surprising. Within twenty-four hours of the explosion strangely coloured suns were seen at enormous distances, up to 2,000 miles, at such widely sundered places as Labuan, Ceylon, and Diego Garcia. The Ceylon observation indeed is open to question, being a

native report from the northern part of the island, and referring to sunrise of the 27th, that is before the major eruption occurred, and unsupported by further testimony from Ceylon and India. It appears certain that already on the 26th vessels 1,000 miles westwards of Java experienced some very singular phenomena, showing the passage overhead of a broad stream of dust from the eruptions of that day, and we may fairly infer that some of the heavier matter composing that dust-cloud fell into a strong southerly wind blowing towards the coast of Ceylon and traversed the distance of about 1,100 miles in about twenty hours. Thus the Ceylon observation, and perhaps Captain Vereker's near Labuan as well, would refer to cloud-streams of dust and steam, of no great magnitude, the one filtered out from a current going rapidly westwards, and the other carried by the S.W. monsoon towards Japan. The early arrival (28th) in Japan of matter causing a coppery sun would be similarly due to the S.W. monsoon bearing the products of the 26th.

The mass of the powdery matter thrown out by the explosion of the 27th seems to have spread out at such an enormous altitude that the finer particles were forthwith conveyed by a full fair easterly gale steadily and without pause on a great circle of the globe. This lofty unresting hurricane has been hitherto unsuspected. No means of ascertaining the winds of inaccessible altitudes in the tropics had been devised by human ingenuity. Nothing but a great natural experiment such as Jules Verne would have hardly dared to dream of would have disclosed the circulation of the upper atmosphere over the greater part of the world, and the disclosure has been made by particles on which, till lately, the 'eternal hills' reposed or floated.

The principal celestial phenomena in the Indian Ocean from August 27 to 30 were, a peculiar lofty haze, a very strange appearance of the sun, and a wonderful red glow long before sunrise and after sunset. The general list or first appearances gives, as far as possible, the words of observers used at the time, and we thus get a very interesting impression both of the various features of the phenomena and of the way in which they struck various minds. The captain of the Barbarossa,' nearly 1,000 miles from Krakatoa, saw the whole sky of a peculiar red, like bright 'polished copper,' and this colour suddenly changed to uniform grey. This appearance was followed by frequent, but strikingly short, thunder,' in reality, the noise of the eruptions of the night of the 26th. The same evening, still further west, the

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sky was all of a flare.' On the 28th, at 1,200 miles due west of the volcano, the sky was very hazy, and a fine white powder fell in a constant shower like snow, covering the whole ship. Many other ships had similar experiences. The sun was nearly obscured by a pale yellowish haze on the 29th and 30th. At about 1,800 miles west a quantity of light dust, like Portland cement, fell at the same time. So late as September 8 a deposit of sand occurred on board the 'Scotia' in 10° N. 53° E.; at the same time a partial halo formed round the sun, and the moon was green before setting; on the following morning the sun was green, and the sky for several days was covered with haze. In the Atlantic, at St. Helena, on August 30, a red light like a distant fire surprised one of the inhabitants at 4 A.M., and on the same day a remarkable glare and leaden sky were noticed in other parts of the Atlantic within the tropics. On the following day, so far as 13° 30' N. 31° 20′ W., a curious electric light appearance' and other phenomena were noted; and near the equator the sun was like copper, with a metallic haze over the sky. On September 2, at 10° S. of the equator, the sun was like polished lead, and the whole sky grey, and on the same day the whole of the northern part of South America was astonished with blue suns, or red skies. These phenomena continued their rapid course westwards, and by September 7 seem to have covered nearly the whole of the Pacific within the same latitudes. On September 9 and 10 green and blue suns were observed over nearly the whole of India; the dust cloud was already well advanced on its second circuit of the globe. On the 22nd the green suns returned in force to India; the stream of matter was now on its third circuit, and can be traced to the Western Atlantic on September 28; after this, its increasing tenuity prevented further observations definite enough to be used in the tables of velocity. During the whole of its rapid and wonderfully even revolution round the earth, the great cloud was extending itself less conspicuously towards the north and south, and many scattered observations in the temperate zones afford evidence that the sifting out of heavier particles continued without interruption, and that these, in sufficient quantity to produce moderate afterglow, were carried by the anti-trades and other elevated currents to great distances. During October the spread of the immense stratum of particles of extreme tenuity which gave rise to most of the phenomena was slow and gradual. There are many indications, and the authors conclude that they repre

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