2 8o 



NA TURE 



[July 17, 1884 



May 20 the Actcea was in 6° 50' S. and 104 2' E., and on the 

 morning of that day a "peculiar light green colour" was ob- 

 served in the sky to the east-south-east, while " from east to 

 east-north-east there was a dark blue cloud, which reached 

 from the horizon to the zenith." "About 2 p.m. it was quite 

 dark. What appeared to be a rain squall rose up from the 

 east, but, instead of rain, a kind of very fine dust commenced 

 to fall, and very soon everything was covered ; ships, sails, 

 rigging and men were all dust colour ; nothing could be seen 

 100 yards off. The fall continued steadily all night, and 

 stopped about 9 a.m. on Monday the 21st. When we saw the 

 sun it looked like dull silver. At noon we were in Iat. 8° 15' 

 S. and long. 102° 28' E., distant from Java Heads about 170 

 miles. The sky all round remained a dusty hue, and small 

 quantities of dust again fell during the night. The sky did not 

 assume a natural appearance till the 23rd." At a meeting of 

 this Society held on July 12, the Secretary called attention to 

 Capt. Walker's letter, and said there was little doubt that the 

 dust in question had come from Krakatoa, as, according to a 

 note in Nature of June 7, a volcano in that island was in full 

 eruption. From that time accounts of pumice and ashes ob- 

 served in the Indian Ocean had been extracted from log-books, 

 and they showed that on several occasions vessels had passed 

 through fields of pumice long before the great eruptions of 

 August 26 and 27. After that month the reports became more 

 frequent, and they still continued, the latest being from the 

 vicinity and shores of Mauritius, where, since the middle of 

 February, large quantities of pumice had been seen. It would 

 appear, however, that fields of pumice had passed Mauritius 

 long before February, for "a large quantity of pumice-stone and 

 lava was washed up on the beach at Durban (Natal) on 

 October 23." According to the reports received, fields or lanes 

 of pumice had been observed in different parts of the Ocean 

 from 105 to 48° E. and 6° to 12° S. Farther south the extent 

 in longitude had been apparently less. 



That the remarkable sunrises and sunsets which had been 

 observed over a great part of the world after August 27 were 

 due to matter ejected from Krakatoa seemed to be generally 

 admitted. The few who objected to the volcanic dust theory 

 had not proposed any other theory that so completely accounted 

 for the facts. The presence of vapours and finely-divided dust 

 at certain elevations would, as a consequence of known physical 

 laws, produce all the chromatic effects that had been seen and 

 described, and it was known that immense quantities of matter 

 had been shot up from Krakatoa. Similar phenomena had been 

 witnessed by observers between whom and the sun volcanic dust 

 passed, as on the occasion of an eruption of Cotopaxi a few 

 years ago. But it was not necessary to go so far back. From 

 May 20 to 22 last, after an eruption of Krakatoa, Captain 

 Walker, as already stated, observed that to the east-south-east the 

 sky was of a light green colour, that on the 21st the sun looked 

 like dull silver, that the sky all round was of a dusty hue, and 

 that it did not assume its natural appearance till the 23rd. That 

 was perhaps the earliest instance of the chromatic effects of the 

 Krakatoa dust and vapours. Immediately after the eruptions 

 of August 27 they were more intense and on a greater scale. At 

 the Seychelles on the 27th the sky, according to Mr. Estridge, 

 was hazy all day. The sunset on that day was gorgeous ; the 

 sky was lurid all over, and beams of red light stretched from 

 over St. Anne's to nearly the horizon. At sunset on the 28th 

 the sun looked as it did through a fog on a frosty day in Eng- 

 land. On the morning of the 29th the sun at 7 a.m. was more 

 like a full moon than anything else. According to other letters 

 from the Seychelles the sun for a whole week appeared dim. 

 At Rodrigues, according to Mr. Wallis, whose report was written 

 on August 31, the sky at north-west on every evening since the 

 27th had a very threatening and strange appearance of a deep 

 purplish red colour, which lasted till 7. 15 p.m., and which, with 

 the disturbances of the sea water, caused much fear and excite- 

 ment. Similar phenomena were observed on the same evenings 

 at Diego Garcia and St. Brandon, and for several days the sun 

 looked as if partially obscured. At Mauritius the sky was over- 

 cast throughout the whole of the 27th, and it was observed and 

 noted at the time that there was an unusual dimness. On the 

 evening of the 28th there was a gorgeous sunset, the first of a 

 long series of remarkable colorations and glows, which had 

 already been described. Observations of these optical phenomena 

 had been taken daily during nearly the last nine months when- 

 ever the weather permitted. Knowing what had been observed 

 on board of the Actcea, and that Krakatoa had been in eruption, 



these extraordinary sunsets and sunrises were attributed to the 

 presence in the upper strata of the air of finely-divided matter, 

 and probably gases and vapours, from Krakatoa, and subse- 

 quent events confirmed that opinion. It was difficult to explain 

 phenomena which had been identical under all conditions of 

 weather, and in many distant places, by any purely meteoro- 

 logical causes. To the meteoric dust theory it might be ob- 

 jected that it was purely an hypothesis almost, if not wholly, 

 unsupported by facts. No unusual number of meteors had been 

 seen. No extraordinary glows had been observed at or near the 

 times of the great meteoric showers of November 1866, and 

 November 1872. Moreover one would suppose that if the earth 

 had for months been passing through volumes of meteoric dust 

 the chromatic effects would have appeared simultaneously 

 wherever the sun rose and set. But such had not been the case. 

 Upon the whole there seemed to be a preponderance of evidence 

 in favour of the volcanic dust theory. The objection that the 

 quantity of matter was insufficient was not a formidable one, for 

 the effects did not depend merely upon the quantity of matter 

 that had reached the higher regions, but also upon its form and 

 degree of tenuity. A few pounds of matter might be spread 

 over thousands of square miles. As to the objection that it was 

 difficult to conceive how even finely-divided matter could remain 

 so long in suspension, it might be remarked that, independently 

 of the possibility of the particles being electrified, the lower 

 strata of the atmosphere might be denser than the foreign matter 

 in the upper strata. The extraordinary sunsets and sunrises 

 which were observed in 1783-84, and which Arago and others 

 ascribed to volcanic dust, were said to have lasted eleven months. 

 Those of 1883-84 would probably last fully as long. Within 

 the last few weeks there had been at Mauritius a considerable 

 increase in the intensity and duration of the glows. 



EVIDENCES OF THE EXISTENCE OF LIGHT 



AT GREAT DEPTHS IN THE SEA ' 

 "THE evidences of the presence of light and its quality and 

 *■ source at great depths are of much interest. At present 

 very little experimental knowledge in regard to these questions 

 is available. That light of some kind, and in considerable 

 amount, actually exists at depths below 2000 fathoms, may be 

 regarded as certain. This is shown by the presence of well- 

 developed eyes in most of the fishes, all of the cephalopods, 

 most of the decapod Crustacea, and in some species of other 

 groups. In many of these animals, living in 2000 to 3000 

 fathoms, and even deeper than that, the eyes are relatively 

 larger than in the allied shallow-water species ; in others the 

 eyes differ little, if any, in size and appearance, from the eyes of 

 corresponding shallow-water forms ; in certain other cases, 

 especially among the lower tribes, the eyes are either rudi- 

 mentary or wanting in groups of which the shallow-water repre- 

 sentatives have eyes of some sort. This last condition is notable 

 among the deep-water gastropods, which are mostly blind ; but 

 many of these are probably burrowing species ; and it may be 

 that the prevalent extreme softness of the ooze of the bottom, 

 and the general burrowing habits, are connected directly with 

 the habits or rudimentary condition of the eyes in many species 

 belonging to different classes, including Crustacea and fishes. 

 Such blind species usually have highly developed tactile organs to 

 compensate for lack of vision. 



Other important facts bearing directly, not only on the 

 existence, but on the quality, of the light, are those connected 

 with the coloration of the deep-sea species. In general, it may 

 be said that a large proportion of the deep-sea animals are highly 

 coloured, and that their colours are certainly protective. Certain 

 species, belonging to different groups, have pale colours, or are 

 translucent, while many agree in colour with the mud and ooze 

 of the bottom ; but some, especially among the fishes, are very 

 dark, or even almost black ; most of these are probably instances 

 of adaptations for protection from enemies, or concealment from 

 prey. But more striking instances are to be found among the 

 numerous brightly-coloured species belonging to the echinoderms, 

 decapod Crustacea, cephalopods, annelids, and Anthozoa. In 

 all these groups, species occur which are as highly coloured as 

 their shallow-water allies, or even more so. But it is remarkable 

 that in the deep-sea animals the bright colours are almost always 

 shades of orange and orange-red, occasionally brownish red, 

 1 From a paper in Science, July 4, on " Results of Dredgings in the Gulf 

 Stream Region by the U. S Fish Commission." 



