Oct. 4, 1888] 



NA TURE 



54i 



Although, therefore, as time progresses, and human 

 knowledge changes and enlarges, some of the conclusions 

 drawn by the authors of the Report may be modified or 

 reversed, the value and permanence of the facts and 

 opinions quoted, will be secured by the unusual care 

 which Mr. Symons has taken to verify all the references 

 and quotations. 



The work is divided into five parts : — 



I. On the volcanic phenomena of the eruption, in- 

 cluding the nature and distribution of the ejecta, by Prof. 

 Judd, F.R S. 



II. On the air-waves and sounds caused by the erup- 

 tion, prepared under the direction of Lieut.-General R. 

 Strachey, F.R.S. 



III. On the seismic sea-waves caused by the eruption, 

 by Captain W. J. L. Wharton, R.N., F.R.S. 



IV. On the unusual optical phenomena in the atmo- 

 sphere which began in 1883 and continued in part up to 

 1886 inclusive, and which included coloured suns, twilight 

 effects, coronal appearances round sun and moon, sky 

 haze, &c, by the Hon. F. A. Rollo Russell and Mr. E. 

 Douglas Archibald. And 



V. A short discussion of the magnetical and electrical 

 phenomena, by Mr. G. M. Whipple. 



Prof. Judd commences by pointing out how peculiarly 

 favourable for the gigantic outburst was the position 

 occupied by Krakatao. The marked linear arrangement 

 of the volcanoes of Java and Sumatra points to the exist- 

 ence of a corresponding great fissure in the earth's crust ; 

 while across the Straits of Sunda lies another line of 

 weakness, along which five volcanoes have been thrown 

 up at different epochs. KrakataT) lies precisely at the 

 intersection of these lines. It is therefore a position 

 where volcanic action, once having commenced, might 

 be expected to display itself on its grandest and most 

 intense scale. 



The history of Krakatao, as traced by Prof. Judd, 

 shows that, both in dimensions and activity, it may be 

 considered to have been one of the largest and most de- 

 structive volcanic craters in the world. At one time, " its 

 circumference, at what is now the sea-level, could not 

 have been much less than twenty-five miles, and its height 

 above the same datum plane was perhaps not less than 

 10,000 to 12,000 feet." 



Then, at some unknown period, a terrible outburst 

 seems to have occurred, far transcending the present one, 

 which completely eviscerated the volcano, and reduced it 

 to the condition of a basal wreck of three islands, one of 

 which contained Rakata, a basaltic lava cone from which 

 the island derived its name, and two smaller parasitical 

 cones ; while the other two represented the relics of the 

 original crater, formed of the same material as the latter, 

 viz. enstatite dacite. The relatively inconspicuous cha- 

 racter of Rakata, and the adjacent cones and islets, as 

 well as the absence of any serious volcanic action since 

 1680, seem to have warded off any suspicions which 

 might have been entertained by the inhabitants on the 

 adjacent coasts regarding either the former grandeur of 

 the volcano or the possible renewal of its activity, 

 certainly on such a scale as was witnessed on August 27, 

 1883. . 



Nature, however, rarely displays its grandest effects 

 without giving premonitory warnings, and, in volcanic and 

 seismic phenomena more particularly, by exhibiting the 

 culminating outburst as the cumulative result of an aggre- 

 gation of small and continuously operating hypogenic 

 causes. 



For some years prior to 1883, earthquakes had been of 

 frequent occurrence in the vicinity, one of which destroyed 

 the lighthouse on Java's First Point, and was felt even in 

 North Australia, while on May 20 and 21 an eruption 

 proceeded from Perboewatan, the most northern of the 



three craters which occupied the place of the original 

 prehistoric volcano, and the same that was in erup- 

 tion in 1680. This eruption, though only of a relatively 

 mild (Strombolian) type, compared with its successor, was 

 yet sufficiently striking to be accountable for some of the 

 sporadic sky effects which, as we shall see, were noticed 

 in its vicinity during and for some little time after its 

 occurrence. For example, the captain of the German 

 ship Elizabeth, when passing through the Straits on 

 May 20, observed the height of the smoke column as it 

 issued from the volcano to be over 30,000 feet, and found 

 dust fall on his ship when it was more than 300 miles 

 distant ; while, according to Verbeek, the writer of the 

 Dutch Report, the sounds were heard not merely at 

 Batavia and Buitenzorg, 100 miles off, but even at 

 Singapore, which is 518 miles away. 



After this relatively minor, though absolutely violent 

 eruption, a period of intermittent and subordinate activity 

 prevailed, during which two other dormant cones re- 

 opened, the decrease in violence being thus probably 

 made up for by the larger area in eruption. Finally, after 

 a period of growing intensity — a fact which was attested 

 by observations at Batavia and on board ships passing 

 through the Straits — the entire volcano appears, on 

 August 26, to have passed from the moderate (Strom- 

 bolian) stage to the paroxysmal (Vesuvian) stage. 



It would be unnecessary to recapitulate the accounts 

 given of this terrific outburst, which lasted from 2 p.m. on 

 Sunday, August 26, to the evening of August 27, and 

 reached its culmination at about 10 o'clock on the latter 

 day. The originals read like romances from the "Arabian 

 Nights,'' though to attempt to adequately describe such a 

 chaos would need the pen of a Dante coupled with the 

 pencil of a Dore". The salient features were ( 1) the unusual 

 height to which the smoke column was observed to 

 ascend, viz. seventeen miles, by Captain Thomson, of the 

 Medea — the nearest approach to which on any former 

 occasion seems to have been thirteen miles at the eruption 

 of Graham's Island (Julia) in 1831 ; (2) the extraordinary 

 violence of the detonations; and (3)the accompanying atmo- 

 spheric and electric phenomena. With respect to this latter 

 point, the volcano was, in fact, a frictional hydro-electric 

 generator of electricity on the largest possible scale. 



One of the most important deductions arrived at by 

 Prof. Judd from a study of this and other eruptions is the 

 precise part played by water in aiding eruption. 



It appears to be often thought that both slow percola- 

 tion and the rapid introduction of water into reservoirs of 

 lava are the direct causes of eruption ; but Prof. Judd 

 shows that, while the percolation of water is one of the 

 contributory causes, it is not the primary cause, which he 

 attributes, when discussing the nature of the materials 

 ejected, to "the disengagement [by heat] of volatile 

 substances actually contained in those materials." . 



According to this, which may be termed the " cart- 

 ridge" doctrine of eruption (the lava representing both 

 the powder and shot), the action of inrushes of sea- 

 water, such as occurred in the present case, by chilling the 

 surface of the lava, and augmenting the tension of the 

 imprisoned gases, caused '" a check and then a rally," 

 analogous to what occurs in a geyser when sods are 

 thrown into it. Prof. Judd attributes the excessively 

 violent nature of the last stages of the great eruption of 

 Krakatao to this " check and rally action," caused by the 

 dissolution after evisceration of the crateral framework of 

 the volcano, and the consequent admission of the sea in 

 large quantities, a circumstance to which its position 

 rendered it peculiarly accessible. 



Prof. J udd considers the " excessively violent though short 

 paroxysms with which it terminated " to be the special 

 feature by which the eruption of Krakatao differed from 

 others of similar rank. These, while characterized by a 

 larger quantity of materials ejected, present no parallel to 



