A MIGHTY SEA-WAVE. 



175 



crests to raise the water-surface, while in the 

 middle of the net (not the middle of the sides, 

 but the middle of the space inclosed by the four 

 sides) trough joins with trough to depress the 

 water-surface. 1 



We must take into account the circumstance 

 that the wave which reached Hawaii last May 

 was probably reflected from the California coast, 

 when we endeavor to determine the rate at which 

 the sea-disturbance was propagated across the 

 Atlantic. The direct wave would have come 

 sooner, and may have escaped notice because 

 arriving in the night-time, as it would necessarily 

 have done if a wave which traveled to California, 

 and thence, after reflection, to the Sandwich 

 group, arrived there at a quarter before five in 

 the morning following the Peruvian earthquake. 

 We shall be better able to form an opinion on 

 this point after considering what happened in 

 August, 1868. 



The earth-throe on that occasion was felt in 

 Peru about five minutes past five on the evening 

 of August 13th. Twelve hours later, or shortly 

 before midnight, August 13th, Sandwich Island 

 time (corresponding to 5 A. M., August 14th, Pe- 

 ruvian time), the sea round the group of the Sand- 

 wich Isles rose in a surprising manner, " inso- 

 much that many thought the islands were sink- 

 ing, and would shortly subside altogether beneath 

 the waves. Some of the smaller islands were for 

 a time completely submerged. Before long, how- 

 ever, the sea fell again, and as it did so the ob- 

 servers found it impossible to resist the impres- 

 sion that the islands were rising bodily out of 

 the water. For no less than three days this 

 strange oscillation of the sea continued to be ex- 

 perienced, the most remarkable ebbs and floods 

 being noticed at Honolulu, on the island of Oa- 

 hu." 



The distance between Honolulu and Arica is 

 about 6,300 statute miles ; so that, if the wave 

 traveled directly from the shores of Peru to the 

 Sandwich Isles, it must have advanced at an av- 

 erage rate of about 525 miles an hour (about 450 

 knots an hour). This is nearly half the rate at 

 which the earth's surface near the equator is car- 



1 The phenomena here described are well worth ob- 

 serving on their own account as affording a very in- 

 structive and, at the same time, very beautiful illustra- 

 tion of wave-motions. They can be well seen at many 

 of our watering-places. The Fame laws of wave-mo- 

 tion can be readily illustrated, also, by throwing two 

 stones into a large, smooth pool at points a few yards 

 apart. The crossing of the two sets of circular waves 

 produces a wave-net, the meshes of which vary in 

 shape according to their position. 



ried round by the earth's rotation, or is about the 

 rate at which parts in latitudes 62° or 63° north 

 are carried round by rotation ; so that the mo- 

 tion of the great wave in 1868 was fairly com- 

 parable with one of the movements which we are 

 accustomed to regard as cosmical. We shall 

 presently have something more to say on this 

 point. 



Now, last May, as we have seen, the wave 

 reached Hawaii at about a quarter to five in the 

 morning, corresponding to about ten, Peruvian 

 time. Since, then, the earthquake was felt in 

 Peru at half-past eight on the previous evening, 

 it follows that the wave, if it traveled directly 

 from Peru, must have taken about thirteen and a 

 half hours, or an hour and a half longer, in trav- 

 eling from Peru to the Sandwich Isles, than it 

 took in August, 1868. This is unlikely, because 

 ocean-waves travel nearly at the same rate in the 

 same parts of the ocean, whatever their dimen- 

 sions, so only that they are large. We have, 

 then, in the difference of time occupied by the 

 wave in May last and in August, 1868,, in reach- 

 ing Hawaii, some corroboration of the result to 

 which we were led by the arrival of the wave 

 simultaneously at all the islands of the Sandwich 

 group — the inference, namely, that the observed 

 wave had reached these islands after reflection 

 from the California shore-line. As the hour when 

 the direct wave probably reached Hawaii was 

 about a quarter-past three in the morning, when 

 not only was it night-time, but also a time when 

 few would be awake to notice the rise and fall of 

 the sea, it seems not at all improbable that the 

 direct wave escaped notice, and that the wave 

 actually observed was the reflected wave from 

 California. The direction, also, in which the os- 

 cillation was first observed corresponds well with 

 this explanation. 



It is clear that the wave which traversed the 

 Pacific last May was somewhat inferior in size to 

 that of August, 1868, which, therefore, still de- 

 serves to be called (as then by the present writer) 

 the greatest sea-wave ever known. The earth- 

 quake, indeed, which preceded the oceanic dis- 

 turbance of 1868 was far more destructive than 

 that of May last, and the waves which came in 

 upon the Peruvian and Bolivian shores were 

 larger. Nevertheless, the wave of last May was not 

 so far inferior to that of August, 1868, but that 

 we may expect to hear of its course being traced 

 athwart the entire extent of the Pacific Ocean. 



When we consider the characteristic features 

 of the Peruvian and Chilian earthquakes, and 

 especially when we note how wide is the extent 



