Oct. 22, 1885 | 
NATOGRE 
603 
greatest, and it is probable that the air-wave then 
formed made the tour around the world. Forty places 
in Europe, America, and Australia are named where 
the disturbance of the air has been indicated by baro- 
meters, and with the help of these data the author 
has been able to calculate the velocity of the air move- 
ment, which has been found to be considerably less 
than the velocity of sound at o C.; consequently the 
movements took place at a great height and in cold-air 
strata. 
According to the author’s calculation this air-wave re- 
quired 354 hours to make the circuit of the earth; it 
would have been of great interest to know just when the 
wave returned to Batavia, but, unfortunately, the diagrams 
of the indicator at the gasworks that might have marked 
such a return have been lost. 
Part of Chapter V. treats of changes in the sea-bottom. 
The sea now covers to a depth of 200 to 300 metres what 
was formerly the northern part of Krakatao, and the small 
island called Polish Hat has also disappeared. Between 
the remaining islands, which are fragments of the old 
crater ring, an area has subsided of at least 41 square 
kilometres, or about 10,000 acres. Outside these islands, 
within a triangular space of 34 square kilometres, the sea 
is also deeper than formerly, so that altogether a surface 
of 75 square kilometres has subsided, which is clearly 
shown on maps 1, 2, and 4. 
The part of the Peak which has disappeared must have 
been 1 cubic kilometre in size, and the fall of such a mass 
into the sea is quite sufficient to cause the great sea-wave 
which swept away thousands of human beings. Nowhere 
is there the slightest vestige of any upheaval, from which 
we may be certain that no seismic movement of the sea- 
bed has occurred. In Bantam and in the Lampong 
districts, after the disaster, the remains of the macadam- 
ised roads along the coast were everywhere as high above 
the sea as before, and soundings in Sunda Straits showed 
that no change of sea-bottom has taken place there. The 
shallower depth in the immediate vicinity of Krakatao, 
and between Krakatao and Sebesi, has probably been 
the result of fallen materials, to which also the islands 
Steers and Calmeyer, which have since disappeared, for 
the greater part, no doubt owed their existence. 
As the last of the phenomena which accompanied the 
eruption of 1883, the movements of the sea are discussed, 
as shown by the destructive waves which have made this 
catastrophe so terrible. It is certain that the greatest 
wave of all started from Krakatado at 10 a.m., and that 
wave completed the destruction of Telok Betong, Anjer, 
and Tjiringin. This great wave had been preceded by 
small waves on Sunday afternoon at 6, and Monday 
morning at 6h. 30m., by which these places were already 
partly submerged and destroyed; but the really very 
remarkable phenomenon was observed that not every 
wave reached all the places situated along the coasts of 
the Straits of Sunda. For example: the wave which 
destroyed on Monday morning, at 6, a part of Anjer, and 
at 6h. 30m. the lower part of Telok Betong, has not been 
noticed at Tjiringin. The author explains this by the 
supposition that the preceding waves were not caused by 
the falling in of parts of the volcano, but by the enormous 
quantities of ejected matter that splashed into the sea. 
Suppose on Sunday evening during the eruption of 5h. 7m. 
a large quantity was thrown out on the spot where Calmeyer 
lies, the wave thus formed was noticed everywhere around 
—at Merak, Anjer, Tjiringin, Beneawang, Telok Betong, 
and Ketimbang. If, during the eruption on Monday 
morning (5h. 30m.), the matter was thrown down on the spot 
where Steers lies, then the wave would be obstructed in a 
south-easterly direction by Calmeyer, and Tjiringin, lying 
behind it, be protected, whilst the wave would roll to 
Anjer, where it must have arrived a little after 6 a.m. In 
like manner, at the explosion of Monday morning (6h. 44m.), 
Anjer and Tjiringin were protected by Krakatdo, and 
Telok Betong by Lagoendie, whilst Beneawang in the Bay 
of Semangka was nearly destroyed; but the wave of 
10 o’clock being of such enormous magnitude, swept over 
all obstacles. 
Most careful calculations fix the time of the formation 
of the great wave at 10 a.m., the same hour at which the 
heaviest detonation was heard, so that the ejection of a 
stupendous quantity of ashes, pumice, and mud, the 
rushing in of the sea upon the mass of glowing lava, and 
the falling in of half the mountain, must have taken place 
almost simultaneously. From the height registered by 
the tide-gauges at Tandjong-Priok on Monday at 7h. 30m. 
p.m. it is evident that Batavia narrowly escaped a second 
inundation. The data collected from all parts of the 
world regarding an extraordinary movement of the sea 
soon after the eruption, made it possible to compute the 
velocity of the great wave, and this velocity enabled the 
author to calculate the average depth of the sea along 
the path the wave travelled. In this way he has ascer- 
tained that the depth of the sea between Krakatao and 
South Africa must amount to 4200 metres; between 
Krakatado and Rodriguez, 4560; and between Krakatao 
and South Georgia, 6340 metres ; which shows that west 
and south-west of Australia there must be a deep-sea basin, 
the existence of which has not yet been revealed by 
soundings. Mr. Verbeek considers that, if the irregu- 
larities of the tide noticed at Aspinwall happened at the 
hour reported, they were not caused by the Krakatao 
wave, but by volcanic activity in the Antilles ; that wave, 
however, was observed on the coast of France, at San 
Francisco, and even in Alaska. Its velocity was so great 
that it reached Aden in twelve hours, a distance of 3800 
nautical miles, usually traversed by a good steamer in 
twelve days. 
It is greatly to be regretted that our knowledge of this 
phenomenon beyond the Indian Ocean remains incom- 
plete, on account of the small number of tide-gauges on 
the Atlantic and Pacific coasts; the author suggests that 
this want shall be promptly supplied, so that in future no 
important movement of the sea shall escape notice. 
Chapter VI. is devoted to a consideration of the vol- 
canic phenomena which have been observed during the 
eruption of Krakatad at other (places within or beyond 
the Indian Archipelago. Simultaneously the volcano 
Goenong Api, on the island of Great Sangi, the Merapi 
on Java, the Merapi on Sumatra, and also, it is supposed, 
a volcano in the Moluccas were in activity. A seismic 
movement of the sea-bottom occurred in the whole 
region of the Moluccas, which could not have been due 
to Krakatao, and this movement has been noted by three 
tide gauges in the Straits of Madura. Over a large part 
of Australia, from August 27 to 29, more or less serious 
earthquakes were felt—a phenomenon the more remark- 
able because Australia suffers very seldom from any 
shaking of the earth. It is probable that sudden displace- 
ments of steam—perhaps of lava—occurred in the sub- 
terranean cavities, caused by a change of pressure 
through the great discharge of lava and steam at 
Krakatao. We must therefore conclude that the under- 
ground recesses between Krakatao and Australia are in 
some way connected, so that any change of pressure in 
one cavity causes a change of pressure in the other. 
Even at points in the neighbourhood of the antipodes 
of Krakatad shocks and volcanic effects were noticed, 
and if, as is probable, some point in the Antilles was in 
activity, then evidently the whole surface of the earth 
during the terrible discharge of Krakatao was agitated, 
and apparently the crust of our earth is not so solid as 
many of its inhabitants fondly imagine. 
The author maintains the doctrine that part of our 
globe remains still in a molten state, and he disputes the 
theory, which has been advanced, that the heat of the vol- 
canic furnaces is entirely due to local chemical action. He, 
however, acknowledges that it is very difficult to explain 
