2l8 



SCIENCE. 



[Vol. XII. No. 301 



ena following the eruption of Krakatoa on Aug-. 27, 1883, became 

 first known, and when the optical phenomena attracted increasing 

 attention of the whole civilized world, the Royal Society of Eng- 

 land, on Jan. 17, 1884, passed the following resolution: "Resolved, 

 That a committee, to consist of Sir F. Evans, Professor Judd, Mr. 

 Norman Lockyer, Mr. R. H. Scott, General Strachey, and Mr. G. 

 J. Symons, with power to add to their number, be appointed, to 

 collect the various accounts of the volcanic eruption at Krakatoa. 

 and attendant phenomena, in such form as shall best provide for 

 their preservation, and promote their usefulness." A history of the 

 work of the committee is detailed in the preface, its expansion by 

 fusion with a committee of the Royal Meteorological Society and 

 by election of new members, and its method of proceedings. At 

 the end of November, 1884, the discussion of the data collected 

 was commenced, which were divided into five portions, each going 

 to a separate sub-committee, and each giving a separate report, 

 which forms the present volume. Thus the work is divided into 

 five parts : i. ' On the Volcanic Phenomena of the Eruption, and 

 on the Nature and Distribution of the Ejected Materials,' by Prof. 

 J. W. Judd ; 2. ' On the Air- Waves and Sounds caused by the 

 Eruption,' prepared in the Meteorological Office, and presented by 

 Lieut. -Gen. R. Strachey; 3. 'On the Seismic Sea-Waves caused 

 by the Eruption,' by Capt. W. J. L. Wharton ; 4. ' On the Un- 

 usual Optical Phenomena of the Atmosphere, 1883-86, including 

 Twilight Effects, Coronal Appearances, Sky Haze, Colored Suns, 

 Moons, etc.,' by the Hon. F. A. RoUo Russell and Mr. E. Douglas 

 Archibald ; 5. ' Report on the Magnelical and Electrical Phenom- 

 ena accompanying the Eruption,' by G. M. Whipple. 



While the Dutch report by Verbeek deals with the local phenom- 

 ■ ena, the English committee paid specal attention to the meteoro- 

 logical and other occurrences which took place all over the earth. 



The most interesting part of Professor Judd's account is his 

 theory as to the part played by water in causing or aiding eruptions. 

 He believes that the disengagement by heat of volatile substances 

 actually contained in the lava is the primary cause of volcanic ac- 

 tivity. He proves that the melting-point of all lavas of Krakatoa 

 of different ages, although of the same chemical composition, vary 

 to a great extent according to the amount of water contained in 

 them, their fusibility being greater when water is present. In 

 this case, on melting, they develop a great amount of gases. " In 

 this way the actual nature of the volcanic manifestations at any 

 particular vent are seen to be determined, not so much by the 

 mineralogical constitution of the lava, as by the circumstance of 

 the quantity of water contained in the magma. Where this is 

 great, the lava will be perfectly liquid, and will be almost wholly 

 thrown out in the form of pumice and dust. On the other hand, 

 lavas containing little water will require a very high temperature 

 for their fusion, and they will be characterized by great viscosity 

 rather than perfect liquidity. It is through the introduction of the 

 sea and other surface waters into rock masses by slow percolation 

 from above, and the consequent formation of new compounds, 

 more readily acted upon by subterranean heat, that I am disposed 

 to regard volcanic phenomena as being brought about. In this we 

 find an explanation of the proximity of volcanoes to great bodies of 

 water, which, it seems to me, is far more in accord with the actual 

 phenomena than the supposition that water finds access to volcanic 

 foci by means of actual open fissures." 



Professor Judd shows very clearly that the effect of the inrush of 

 water upon lava is quite different, and, especially in the case of 

 Krakatoa, resulted in the formidable violence of the eruption. 

 When the volcano became so far eviscerated as to give access to 

 the water of the sea, the latter cooled the surface of the mag- 

 ma, and as a result the activity of the volcano diminished. As, 

 however, the disengagement of volatile substances actually con- 

 tained in this material continued, the formation of this crust would 

 have the same effect as fastening down the safety-valve of a steam- 

 boiler, while the fires below were maintained in full activity. This 

 constant augmentation of tension beneath Krakatoa, in the end 

 gave rise to the tremendous explosions which made the eruption of 

 the volcano so remarkable. 



In the second part, General Strachey discusses the remarkable 

 atmospheric oscillations, which, starting from Krakatoa, moved as 

 many as seven times over the earth. Their propagation from the 



volcano to its antipodes and back is shown on a number of inter- 

 esting maps. The principal results of the inquiry into the move- 

 ments of this disturbance are, that it had very nearly the character- 

 istic velocity of sound, ranging from 648 to 726 English miles an 

 hour, and that its mode of propagation by an aerial oscillation of 

 comparatively short duration was also closely analogous to that of 

 sound. Waves travelling with and against the direction of the 

 earth's rotation show differences of velocity of about twenty-eight 

 English miles an hour. This may probably be accounted for by 

 the circumstance that the winds along the paths of this portion of 

 the wave would, on the whole, have been westerly, which would 

 have caused an increase of velocity in the wave moving in the op- 

 posite direction ; so that the observed difference of twenty-eight" 

 miles could be produced by an average westerly current of fourteen 

 miles per hour, which is not unlikely. 



The author continues, " There is some appearance of a greater 

 retardation of the wave in passing in a direction opposed to the 

 earth's rotation over the northern European stations as compared 

 with those in the south of Europe, which may possibly be due to 

 the lower temperature of the more northern part of the zone trav- 

 ersed. This difference is not to be traced in the wave moving in 

 the opposite direction, which may be accounted for by the path of the 

 wave, when approaching Europe from the west, having lain for a 

 long distance over the Atlantic, where the differences of tempera- 

 ture between the northern and the southern borders of the zone 

 traversed would have been relatively small. 



" The path of the wave that passed over the Canadian and 

 United States stations, and Havana, lies nearly on the meridian 

 drawn through Krakatoa, and must have crossed both the polar 

 circles near the poles. The velocities obtained from these stations 

 are peculiar. The direct wave from Krakatoa, which travelled 

 nearly due north and close to the north pole, and its repetitions 

 after passing round the earth in the same direction, had nearly the 

 same velocities as those observed at the European stations, with aii 

 apparent decided retardation in the intervals between the first and 

 third passages, and (but to a less extent) between the third and 

 fifth. The wave that passed through the antipodes before reaching 

 the North American stations went nearly due south close to the 

 south pole; and its velocity on this its first partial passage round 

 the earth was very decidedly reduced ; but in its next complete 

 circuit the velocity appears to have been much increased, almost 

 reaching the full rate of the true sound-wave. It is difficult to ac- 

 count for this, but the fact seems to be indisputable. Probably an 

 explanation of this peculiar feature of the phenomena maybe found 

 in the conditions of the wind and weather in the southern ocean 

 during the days on which the wave passed over it, which are not 

 known to us." 



In the second part of General Strachey 's report a list of places is 

 given at which the sounds of the explosions at Krakatoa were heard 

 on the 25th and 27th of Augtist. In all directions the sound was 

 heard at a distance of two thousand miles from the volcano, while 

 south-westward it was even noticed at Rodriguez, very nearly three 

 thousand miles from Krakatoa. 



Captain Wharton, in his discussion of the seismic sea-waves 

 caused by the eruption, distinguishes two descriptions of waves, — 

 long ones, with periods of over an hour; and shorter but higher 

 waves, with irregular and much briefer intervals. The greatest 

 disturbance which followed the great explosion of the volcano re- 

 sulted in waves about fifty feet high in the Strait of Sunda, and 

 caused the vastest destruction. The speed of both classes of 

 waves was about the same, and it is remarkable that it was in all 

 cases less than the depth of water would demand according to 

 theory. To the north and east in the Java Sea the long wave can 

 be traced for 450 miles, but it was at this distance reduced to a 

 very small undulation. To the west, on the other hand, the long 

 wave travelled over great distances, and reached Cape Horn and 

 the shores of Europe. The shorter waves did not extend beyond 

 Ceylon and Mauritius. South-eastward the disturbance did not 

 continue beyond the west coast of Australia; the disturbances 

 noted in New Zealand and in the Pacific evidently being caused by 

 other seismic action, and having no connection whatever with the 

 eruption of Krakatoa. 



By far the greater portion of the report is taken up by the dis- 



