526 



METEOKOLOGY. 



auroras were seen that could reasonably be 

 associated with it, and no electrical disturb- 

 ances were mentioned in connection with it, 

 except in a single instance by Prof. C. Michie 

 Smith, of Madras. The theory that it is the 

 result of peculiar conditions of vapor in the 

 air receives a partial support from Prof. 

 Smith's spectroscopic observations, in which 

 all the atmospheric lines usually ascribed to 

 aqueous vapor were very strongly developed. 

 A marked general absorption was also ob- 

 served in the red. The facts may also be cited 

 in favor of this theory, that Prof. Lockyer has 

 seen the sun green through the steam of a 

 steamboat; that it has appeared green through 

 the mists of the Simplon; that bright-green 

 suns have been remarked by travelers in the 

 Arctic regions ; and, as stated by the Rev. G. 

 H. Hopkins, of Cornwall, England, that, in a 

 clear sky, when the disk of the sun sinks below 

 the horizontal line of the ocean, the parting 

 ray is a bright emerald-green. It is, however, 

 difficult, on this theory alone, to account for 

 the persistence of the phenomena for so long 

 a period through all the varying conditions 

 of atmospheric pressure. Dr. F. A. Forel, of 

 Merges, Switzerland, mentions, as against the 

 sufficiency of the hypothesis, that in Switzer- 

 land the glow, after having decreased subse- 

 quently to the 3d of December, attained a sec- 

 ond maximum on the 24th and 25th of that 

 month, when the atmospheric conditions were 

 quite different from those which prevailed in 

 the country at the time of the first maximum. 



The hypothesis that the spectacle was caused 

 by the presence in the atmosphere of a cloud 

 of " cosmic dust, " which the earth had met in 

 its course, has received considerable support. 

 It is now believed, on the authority of Prof. 

 Nordenskiold, who has collected and' analyzed 

 a meteoric dust from the snows of unin- 

 habited regions, and of other observers, that 

 the earth is constantly receiving accretions 

 from space of an exceedingly fine matter having 

 a composition like that of meteoric stones. 

 Mr. W. Mattieu Williams, of London, and M. 

 Emile Yung, of Geneva, collected in December 

 unusually large proportions of such a dust 

 from freshly fallen snows the former in his 

 garden, the latter on the steeple of the cathe- 

 dral of Saint Pierre af'les Treize-Arbres," 

 Mont Saleve. 



The theory which has found most general 

 acceptation is, that the phenomena have been 

 produced by the diffusion through the whole 

 atmosphere of the earth of ashes and cinders 

 from the eruption of the volcano of Krakatoa, 

 in the straits of Sunda, which took place on 

 the 26th of August. The most weighty objec- 

 tions to this theory arise out of the difficulty 

 of explaining how the matter ejected from the 

 volcano could have so quickly reached the 

 enormous height at which the source of the 

 glow was certainly situated, and of the difficul- 

 ty of imagining it to remain suspended in the 

 air for so long a time. The eruption from 



Krakatoa, which immensely exceeded in vio- 

 lence any convulsion of the kind known to 

 man, may, however, easily be conceived to 

 have been capable of producing effects far 

 transcending those which could be imagined in 

 connection with any ordinary or with any 

 other extraordinary known eruption. Mr. W. 

 J. Stillman has witnessed explosions of the sub- 

 marine volcano of Santorin that threw masses 

 of rock weighing many tons to a distance of 

 from half a mile to a mile, and clouds of dust 

 to an elevation of from six thousand to ten 

 thousand feet. Such effects, magnified to cor- 

 respond with the grander scale of the Kraka- 

 toa eruption, might furnish the conditions re- 

 quired. Respecting the second difficulty, Mr. 

 W. H. Preece and Dr. William Crookes have 

 shown that finely divided particles of dust 

 having an electrical charge of the same sign 

 as that of the earth, may be kept suspended 

 in the air for an indefinite time by electri- 

 cal repulsion. Prof. S. P. Langley has de- 

 scribed an ocean of dust of this kind which 

 he observed in 1881 from near the summit of 

 Mount Whitney, occupying a stratum of the 

 atmosphere some six or seven thousand feet 

 above the level of the sea, from which light 

 was reflected red. A similar formation has 

 been seen from the Peak of Teneriffe, consti- 

 tuting apparently a permanent constituent of 

 the atmosphere. 



Positive evidence is at hand of the presence 

 during the prevalence of red sunsets of a dust 

 of this kind in the atmosphere of Europe. 

 The sediment derived from a snow that fell at 

 Madrid, Spain, on the 7th of December, when 

 examined, was found to contain, besides the 

 ordinary atmospheric dust of the city, particles 

 of volcanic hypersthene, magnetic iron, and 

 volcanic glass. A rain that fell at Wageningen, 

 Holland, on the 13th of December, left very 

 obvious sediments, which, when analyzed by 

 Messrs. Beyerinck and Van Dam, of the Agri- 

 cultural Laboratory at that place, were found 

 to correspond very closely with ashes brought 

 from Batavia, Java, which were known to have 

 come from Krakatoa ; similar sediments were 

 found at Worcester, England, and Storlvdal, 

 Norway, on -Nov. 17th, and at Gainsborough 

 and York, England, Dec. 12th. 



According to Capt. Sir 0. Fleming Sten- 

 house, who was there at the time, the eruption 

 of Graham's island, in the Mediterranean, in 

 1831, was followed by a series of red sun- 

 sets at Malta. White, in his " Natural History 

 of Selborne," records the prevalence in 1783, 

 from June 23d to July 20th, of a peculiar 

 haze, or smoky fog, during which " the sun at 

 noon looked as black as a clouded moon, and 

 shed a rust-colored, ferruginous light on the 

 ground and floors of rooms, but was particu- 

 larly lurid and blood-colored at rising and 

 setting." All this while, " Calabria and part 

 of the isle of Sicily were torn and con- 

 vulsed with earthquakes ; and about that 

 juncture a volcano sprang out of the sea on 



