Meeson. — On the recent Sun-glows, 381 



appointed a Commission to collect all observations and documents bearing 

 thereupon. It appears that the Krakatoa ashes contain abundance of vitre- 

 ous matter and elongated gas-bubbles enclosed in pumice, volcanic sand, 

 and ashes. The two first-mentioned are almost characteristic, and, if so, 

 make the Krakatoa dust less difficult of identification than one might sup- 

 pose. Diller says he has found glass always most abundant in Krakatoa 

 dust collected on the Java coast ; Macpherson, in dust collected from 

 Madrid, found crystals of hypersthene, pyroxene, magnetic iron, and 

 volcanic glass, all of which Daubree found in the Javan volcanic ashes. 

 Verbeek, by microscopic examination of Krakatoa dust on the spot, found 

 therein glass with oval vacuoles, felspar, pyroxene, and magnetite in grains, 

 and octahedra. He also gives the chemical analysis, which I need not 

 repeat. Unfortunately the enquiry is complicated by the circumstance that 

 the vitreous and mineral fragments found near Krakatoa are similar to 

 those found in deep-sea deposits, i.e., such as have fallen from time to time 

 through countless ages from the air into the sea, and which may be either of 

 meteoric or cosmic origin or both. Further, Mattieu Williams on the 5th 

 December last got a black sediment from 75 ounces of snow which fell at 

 Harrow. In this he found much black oxide of iron readily attacked by the 

 magnet and containing nickel. This, he says, is a characteristic of meteoric 

 iron, and cannot possibly have come from Krakatoa, being too heavy. But 

 too much weight must not be attached to this either, for it is evident that 

 the recent fall of Krakatoa dust in different parts of the world would not be 

 likely to stop the supply of meteoric or cosmic dust that the earth is con- 

 tinually receiving. Altogether, this sixth argument at the present date, in 

 the absence of fuller information, is very difficult to work out, and I do not 

 ask you to lay much stress upon it. 



7. The occurrence, as we have already said, of similar phenomena after 

 the volcanic eruptions of 1783 and 1831, furnishes a strong argument for 

 associating our sun-glows with the Krakatoa eruption, and, of the various 

 materials cast out by Krakatoa, dust seems more likely than water or gas to 

 be the operative cause of the colouring. 



8. The very gradual disappearance of the sun-glows is what we should 

 expect if the volcanic dust theory were a correct one, for the dust would fall 

 from the atmosphere very slowly — the heavier particles first, then those of 

 medium weight, and last of all, and after perhaps a long period of time, the 

 most minute and insignificant. 



9. "Where, as in this case, a proposition does not admit of positive 

 demonstration, the occurrence of a number of arguments all tending to 

 show its probability must be allowed to have preponderating weight — par- 

 ticularly if the objections thereto can be satisfactorily answered. 



