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TEE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



such enormous height at starting, that, after 

 traveling with necessarily diminishing height the 

 whole way to Hawaii, it still rises and falls through 

 thirty-six feet. The real significance of this amaz- 

 ing oceanic disturbance is exemplified by the 

 wave-circles which spread around the spot where 

 a stone has fallen into a smooth lake. We know 

 how, as the circle widens, the height of the wave 

 grows less and less, until, at no great distance 

 from the centre of disturbance, the wave can no 

 longer be discerned, so slight is the slope of its 

 advancing and following faces. How tremen- 

 dous, then, must have been the upheaval of the 

 bed of ocean by which wave-circles were sent 

 across the Pacific, retaining, after traveling 5,000 

 miles from the centre of disturbance, the height 

 of a two-storied house! In 1868, indeed, we 

 know (now even more certainly than then) that 

 the wave traveled very much farther, reaching 

 the shores of Japan, of New Zealand, and of 

 Australia, even if it did not make its way through 

 the East Indian Archipelago to the Indian Ocean, 

 as some .observations seem to show. Doubtless 

 we shall hear, in the course of the next few 

 months, of the corresponding effects of the spread 

 of last May's mighty wave athwart the Pacific, 

 though the dimensions of the wave of last May, 

 when it reached the Sandwich Isles, fell far short 

 of those of the great wave of August 13-14, 1868. 



It will be well to make a direct comparison 

 between the waves of May last and August, 1868, 

 in this respect, as also with regard to the rate at 

 which they would seem to have traversed the dis- 

 tance between Peru and Hawaii. On this last 

 point, however, it must be noted that we cannot 

 form an exact opinion until we have ascertained 

 the real region of Vulcanian disturbance on each 

 occasion. It is possible that a careful examina- 

 tion of times, and of the direction in which the 

 wave-front advanced upon different shores, might 

 serve to show where this region lay. We should 

 not be greatly surprised to learn that it was far 

 from the continent of South America. 



The great wave reached the Sandwich Isles 

 between four and five on the morning of May 

 10th, corresponding to about five hours later of 

 Peruvian time. An oscillation only was first ob- 

 served at Hilo, on the east coast of the great 

 southern island of Hawaii, the wave itself not 

 reaching the village till about a quarter before 

 five. The greatest difference between the crest 

 and trough of the wave was found to be thirty- 

 six feet here ; but at the opposite side of the 

 island, in Kealakeakua Bay (where Captain Cook 

 died), amounted only to thirty feet. In other 



places the difference was much less, being in 

 some only three feet, a circumstance doubtless 

 due to interference, waves which had reached the 

 same spot, along different courses, chancing so to 

 arrive that the crest of one corresponded with 

 the trough of the other, so that the resulting 

 wave was only the difference of the two. We 

 must explain, however, in the same way, the 

 highest waves of thirty-six to forty feet, which 

 were doubtless due to similar interference, crest 

 agreeing with crest, and trough with trough, so 

 that the resulting wave was the sum of the two 

 which had been divided, and had reached the 

 same spot along different courses. It would fol- 

 low that the higher of the two waves was about 

 twenty-one feet high, the lower about eighteen 

 feet high ; but as some height would be lost in 

 the encounter with the shore-line, wherever it 

 lay, on which the waves divided, we may fairly 

 assume that in the open ocean, before reaching 

 the Sandwich group, the wave had a height of 

 nearly thirty feet from trough to crest. We read, 

 in accordance with this explanation, that " the 

 regurgitations of the sea were violent and com- 

 plex, and continued through the day." 



The wave, regarded as a whole, seems to have 

 reached all the islands at the same time. If this 

 is confirmed by later accounts, we shall be com- 

 pelled to conclude that the wave reached the 

 group w-ith its front parallel to the length of the 

 group, so that it must have come (arriving as it 

 did from the side toward which Hilo lies) from 

 the northeast. It was then not the direct wave 

 from Peru, but the wave reflected from the shores 

 of California, which produced the most marked 

 effects. We can understand well, this being so, 

 that the regurgitations of the sea were complex. 

 Any one who has watched the inflow of waves on 

 a beach so lying within an angle of the shore, 

 that while one set of waves comes straight in 

 from the sea, another thwart set comes from the 

 shore forming the other side of the angle, will 

 understand how such waves differ from a set of 

 ordinary rollers. The crests of the two sets form 

 a sort of network, ever changing as each set rolls 

 on ; and considering any one of the four-cornered 

 meshes of this wave-net, the observer will notice 

 that, while the middle of the raised sides rises 

 little above the surrounding level, because here 

 the crests of one set cross the troughs of the 

 other, the corners of each quadrangle are higher 

 than they would be in either set taken separately, 

 while the middle of the four-cornered space is 

 correspondingly depressed. The reason is, that 

 at the corners of the wave-net crests join with 



