JoLY — Notes on Volcamc Ash from Krakatoa. 299 



He records " electrical displays" round the vast column of smoke 

 (steam) ascending from Krakatoa on the evening of the 22nd of August. 

 These took the form of vivid lightning, flashes darting from and around 

 the column. Showers of sand and gravel on the 23rd. The terrific 

 explosions of the 26th and 27th are described as " shaking the ship." 

 He was then some eighty miles off, with an intervening screen of 

 mountainous country. 



"With regard to the presence of Pyrites in the ash, nothing was 

 said about it by M. Eenard in his original Paper (which was not, how- 

 ever, known to the author of these notes at the time of preparing his 

 communication to the Eoyal Dublin Society) ; but in a note appended 

 to a Paper appearing in Nature (April 17th), as the joint production of 

 that distinguished mineralogist and of Mr. Murray, its occurrence is 

 mentioned and dismissed as " accidental." It is, however, not alone 

 present, free, as aggregations of cubes and dodecahedrons, but also as 

 an inclusion in the feldspars and in the hypersthene. Again, its 

 abundant occurrence in the ash received from various localities is 

 observable. Fifty specimens were counted by the author in one of 

 three slides prepared from about half a gramme of the dust from 

 Batavia. The dust had been treated for the removal of glass, feld- 

 spars, and free magnetite. It is hard to see why, under the circum- 

 stances, it should be considered accidental. 



Hematite in thin, blood-red, semi-translucent flakes occurs in the 

 ash. It is neither cleavable perceptibly, nor elastic, and is soluble in 

 hydrochloric acid. It shows no trace of dichroism. 



The very great abundance in the ash of Hyjyersthene, compared to 

 Augite, suggests that the original rock should be considered more of 

 the nature of a hypersthene andesite than an augite andesite. In con- 

 nexion with this point the results of Mr. Whitman Cross' examination 

 of a hypersthene andesite, kindly brought under the author's notice 

 by Professor V. Ball, are of much interest. (Bulletin of the United 

 States' Geological Survey, No. 1, 1883.) 



NOTE ADDED IN THE PEESS. 



M. C. Flammarion, in the Eevue d'Astronomie Populaire, July, 

 1884, p. 265, estimates the probable height of projection of the dust, 

 &c., from Krakatoa as at least 20,000 metres (12^ miles). 



Observations made on board the Elizabeth, on the comparatively 

 insignificant explosion of May the 20th, 1883, gave 11,000 metres as 

 the height of projection on that occasion. 



