Nov. 11, 1869] 
NATURE 
55 
the Pacific by night ; but still enough evidence remains to 
exhibit with sufficient clearness the course which the dis- 
turbance followed, 
Let us first endeavour to form a clear conception of the 
scene of this great manifestation of Nature’s powers. The 
Pacific Ocean is not commonly chosen as the subject of a 
single map, and the maps in our ordinary atlases are not 
calculated to give clear ideas respecting the true shape 
and dimensions of an ocean which is undoubtedly the 
most remarkable physical feature of the whole terrestrial 
globe. I have endeavoured to remedy this defect by the 
accompanying chart, which represents a perspective view 
of that half of the globe to which the Pacific belongs, and 
will serve, I think, to convey a tolerably clear impression 
of the true proportions of this great ocean. 
Near the shore of Peru I have marked the estimated 
region of central disturbance by a white circle. 
The great waves which came surging onwards from the 
centre of disturbance must presently have lost their cir- 
cular figure. On account of their enormous dimensions 
they “felt the bottom,” so to speak, and were more or less 
retarded according as they traversed shallow or deep por- 
tions of the great ocean. 
At Arica the first great shock of the earthquake was 
experienced at about five in the afternoon of August 13th. 
Twenty minutes later an enormous wave fifty feet in 
height swept in over the shores ; and we may assume that 
about this time the waves which were about to traverse 
the Pacific started on their vast career. 
Along the coast of Chili the wave travelled southwards, 
reaching Coquimbo three hours after the catastrophe at 
Arica. One hour later the wave had reached Valparaiso ; 
and yet an hour later the inhabitants of Valdivia—marked 
(1) in the map—were terrified by an inrush of the sea 
which threatened to destroy their town. 
Northwards from Arica the progress of the wave was 
not so carefully timed. On the 14th of August, but at 
what hour is not stated, the shores of Lower California, 
near San Pedro—marked (2) in the map—were swept by 
a wave no less than sixty-three feet in height. 
At midnight of August 13-14, the sea-wave reached the 
Sandwich Isles (3), and from that time until the 16th of 
August the sea around those islands rose and fell in a 
surprising manner. It appeared as though the islands 
were first slowly raised as by some irresistible subterra- 
nean forces, and then suffered to subside until they seemed 
about to disappear for ever beneath the waves ; nor was it 
easy to believe that in reality the sea alone was in motion. 
Yokohama (4) was visited by the wave on August 14th, 
but unfortunately the exact hour is not known, otherwise 
there would have been the means of ascertaining how 
long a wave takes in traversing nearly a complete half of 
the earth’s circumference. 
The Marquesas Isles (5) were visited by waves of enor- 
mous dimensions before midnight of August 13th. Some 
of the islands of this group were indeed completely sub- 
merged by the crests of the principal waves. 
At Opara (6), the coaling-station for steamships plying 
between Panama and New Zealand, nine waves came in 
one after the other, at intervals of twenty minutes, the 
highest sweeping over the coal depot. 
At half-past two on the morning of August 14th, the 
watchman in Apiu, on the island of Opolu (7), aroused 
the frightened inhabitants from their sleep with the cry 
that the sea was coming in upon them; and during the 
whole of that day the sea rose and fell at intervals of only 
fifteen minutes. But the waves reached the Chatham 
Islands (8), though nearly as far from Arica, an hour and 
a half sooner. Three enormous waves rushed in upon 
these islands, one of which, the low-lying Tupunga, was 
completely submerged. Between two and three hours 
later the wave had reached the Fiji Islands (9). 
The shores of New Zealand, and especially those bays 
of the southern island which face towards the east, were 
visited by enormous waves. Between three and four 
o'clock in the morning, the harbour of Lyttleton (10) was 
left completely dry by the retreat of the water, which did 
not return until more than an hour had elapsed. At five 
the water began again to retreat, reaching its lowest point 
an hour later. But at a quarter-past seven and at half- 
past nine, and again at eleven, a great sea-wave swept 
over the bounds of the harbour. 
Lastly, the ocean-wave visited the Australian shores 
near Newcastle (11) at about half-past six in the morning 
of August 14th, the waves gaining in height at each return 
until about half-past eleven, from which hour they slowly 
subsided. 
The chief interest of these results lies in the circum- 
stance that they enable us to form an estimate of the 
depth of the Pacific Ocean. Airy, Whewell, and other 
eminent mathematicians have shown how the velocity of 
sea-waves varies with the depth of the part of the ocean 
they are traversing. Where the breadth of the waves is 
great, as in the tidal wave, a very simple law connects the 
variation of the velocity with that of the depth. Ifa wave 
travels twice as fast in one part of its course as in another, 
it may be assumed that the depth of the ocean is four 
times greater in the former than in the latter part of the 
ocean. A tripled velocity signifies that the depth is nine 
times greater, and so on. With waves of different breadth 
the law is slightly different. But the following table, 
extracted from a larger one in Airy’s paper on sea-waves 
(Encyclopedia Metropolitana), shows how slightly the law 
is affected for waves beyond a certain breadth :-— 
Breadth of the Wave in feet. 
Depth of the 
‘ 2 100,000 1,000,000 10,000,000 
Water in feet. : | ear | tases 
Velocity of Wave per Hour in Miles. 
100 38°66 | 38°66 | 38 66 
1,000 122°18 122°27 12227 
10,000 364°92 386°40 386 66 
100,000 487°79 | I,Ist 11 | I,222°70 
Observe, however, how in this table the wave 100,000 
feet in breadth remains relatively insensible of a change 
of depth from 10,090 feet to 100,000, 
Now, Professor von Hochstetter has carefully estimated 
the velocity of the wave which passed from Arica to the 
points marked (1), (3), (6), (7), (8), (10), and (11) in the 
illustrative map, and his results may be briefly indicated 
as follows :— 
284 sea-miles per hour. 
Rate from Arica to station (1). . . 
» » » 3) +++ 417 » ” 
” ” ” 6)...» 362 ” ” 
” ” » &% ses 358 ” ” 
” ”» ” 8)... 360 ”» ” 
” ” » fre = ++ 316 ” ” 
” ” ” Tt)... 319 ” ” 
It is well to observe, first of all, how well the low rate of 
velocity to Valdivia accords with the theory of sea-waves, 
for this wave travelling along the sea-coast must have 
passed for the most part over shallows. The voyage to 
the Sandwich Isles appears to have been accomplished 
more rapidly than any of the others. Along the line, 
therefore, from Arica to (3), the Pacific has its greatest 
depth. Towards stations (6), (7), and (8), the sea-wave 
sped very swiftly, and here, therefore, the water is still 
deep, though not so deep as along the former route. But 
in voyaging onwards from the neighbourhood of the Chat- 
ham Isles (8) to New Zealand and Australia, the sea-wave 
lost a large portion of its velocity, insomuch that the 
average rate for this distance scarcely exceeds that with 
which the wave passed to Valdivia. 
From these results it would be easy to calculate the 
mean depth of the ocean along the various tracks pur- 
