Mzzsox.—On the recent Sun-glows. 881 
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 
voleanie glass, all of which Daubrée found in the Javan voleanie 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 preponde ting weight—par- 
ticularly if the objections thereto can be nacidiestortty Sw answered, 
