THE RECENT REMARKABLE SUNSETS. 
181 
volcanic matter to be ejected in an eruption to four times the 
height of that inequality. 
Another point of view for this question is a comparison 
with the greatest height that has been attained of balloon 
ascent in the atmosphere, which reached as high as 7 miles 
in one case, or 2 miles above the highest of the mountains, 
in an ascent made by Mr. Glaisher and Mr. Cox at Wolver¬ 
hampton, 5th September, 1862, and the height of 40 miles 
for the volcanic matter is only about five-and-a-half times 
that amount. 
It has been suggested that this volcanic matter was pro¬ 
jected into the atmosphere by the Krakatoa eruption, in the 
form of minute hollow glassy vesicles produced by an explo¬ 
sion of steam at enormous pressure bursting through a bed 
of melted lava, and that these particles remained suspended 
for a long time in the atmosphere, and were caused to take a 
very long time in falling back to the earth on account of 
their extremely small actual weight of material, which would 
be further reduced by the internal vacuum arising from con¬ 
densation of contained steam, and on account of the large 
surface exposed by the hollow vesicles in relation to their 
weight. Also in consequence of the excessive electrical dis¬ 
turbance that accompanied the eruption, these particles 
would be highly electrified, and would, therefore, forcibly repel 
one another, and would also be repelled by the earth, from 
its being in a similar electrical condition; and this state 
would continue for a long time with little diminution, on 
account of the highly rarefied atmosphere being a good insu¬ 
lator, as proved in Mr. Crooke’s radiometer experiments. 
In considering the volcanic force of eruption requisite for 
projecting matter to so great a height as 40 miles, it has to 
be noticed that on account of the reduction in the density of 
the atmosphere, its resistance to the passage of a projected body 
is enormously reduced at that height, the density diminishing 
in a geometrical proportion as the height increases in an 
arithmetical proportion. That the eruption in question of 
the Krakatoa volcano was of a very exceptional character, 
and one of the most extensive on record in the force of the 
explosion, is shown by definite evidence of various kinds. 
More than one half of the island of Krakatoa disappeared in 
the eruption; a great tidal wave of 100 feet in height was 
produced in the ocean, the effect of which extended to 
harbours round the entire circumference of the earth; the 
sound of the explosion was heard at 1200 miles distance, at 
Baugney, on the further coast of Celebes; and the fall of ashes 
extended to a distance of 1000 miles, being received by a 
