180 
THE RECENT REMARKABLE SUNSETS. 
tions agreeing with an average speed of about 70 miles an 
hour. 
These circumstances seem to limit the possible cause to 
something actually local, and the volcanic theory suggests 
that this cause was the discharge into the atmosphere at the 
eruption of Krakatoa, on 26th August, of an enormous 
quantity of volcanic matter, possibly melted lava blown into 
a very finely divided vesicular state by the bursting through 
it of an explosion of steam at a very high pressure ; that 
this erupted matter was projected to an exceptionally great 
height in the atmosphere and formed an immense cloud that 
remained suspended there for a great length of time, on 
account of the slow rate at which the particles would be able 
to fall through the atmosphere, and also the mutual repulsion 
of the particles, and their repulsion by the earth due to a 
highly charged electrical condition from the great electrical 
disturbance accompanying the eruption ; that this cloud of 
erupted matter remained stationary at the spot where it was 
projected in the upper regions of the atmosphere, but that 
the atmosphere at that height does not partake of the full 
velocity of rotation of the surface of the earth and of the 
atmosphere that is in immediate contact with the earth, 
lagging behind about seven per cent, of the equatorial 
velocity of 1000 miles an hour, which resulted in an 
apparent westerly movement of about 70 miles an hour; 
according with the westward travelling of the special pheno¬ 
menon that was observed for as great a distance as three- 
quarters round the earth at an approximately uniform rate of 
motion; that the mass of suspended matter became gradually 
and slowly diffused laterally in the atmosphere, being assisted 
in northward and southward dispersion by the continuous polar 
currents of the upper regions of the atmosphere, due to the 
vertical displacement of heated atmosphere rising in the 
equatorial region, and causing the phenomenon to become 
visible successively at places more and more distant from the 
equator. 
Such a height in the atmosphere as 40 miles above the 
earth’s surface appears on first impression to be extravagantly 
great; but when looked into it will be seen to be not 
unreasonable in comparison with the known dimensions of 
inequalities of the earth’s surface. The highest mountains 
reach about 5 miles vertical height, and the greatest depths 
of the sea also reach about 5 miles, making together 10 miles 
inequality of the earth’s surface. The 40 miles height in 
the atmosphere is only four times this amount, and when 
looked at together it does not appear too much to suppose 
