152 



NATURE 



[yune 1 6, 1887 



I am indebted to M. Perrotin, of the Nice Observatory, for 

 some useful information. He tells me that "the first shock 

 lasted ttearfy one minute ; it began by being very slight at first, 

 and then became very intense : this latter phase lasted from 20 

 to 30 seconds. " 



We were all accused of great exaggeration in our accounts of 

 the earthquake (I put the first shock at half a minute), but this 

 more than confirms our estimates. A gentleman from South 

 America, accustomed to earthquakes every week, told us that it 

 was " a pretty good shake up." 



According to Lyell, Mallet, and others, we at Nice being on 

 alluvial deposits— gravel, clay, &c., — felt not only the original 

 shock, but also the rebounds from the rocks on either side ; this 

 would account for the very violent shaking that we had. I have 

 comparsd notes with dozens of people, and feel sure that it was 

 quite different from the sort of shock they felt at Cannes, Monte 

 Carlo, and other places on rock, even the east bay at Mentone 

 (the west bay suffered more than Nice). What saved us from 

 being knocked down was, I suppose, that the amplitude of the 

 vibrations was small, probably only a few inches. In the Italian 

 Riviera (Diano Marina, &c.) they must have been more severe. 

 Most people think that one more shock of the same strength 

 would have brought half the houses down. A railway carriage 

 going at 60 miles an hour gives the best idea of what our rooms 

 were like during the first shock ; it was impossible to stand on 

 the floor without holding on to something, like a landsman on 

 board a ship in a storm. 



It would appear from the times given in the table that the 

 velocity of this earthquake was high : 76 miles a minute to 

 Paris, and 81 to London — a curious case of velocity increasing 

 with distance. 



The second shock seems to have gone faster than the first. 

 The ordinary rate of earthquake-shock velocity is (according to 

 Prestwich's " Geology ") : — 



1857. Neapolitan earthquake 

 1843. United States ,, 

 1869. Cachar (India) ,, 



9 miles per minute. 

 32 „ 

 83 „ 



The centre of the shock was somew«here in the Gulf of Genoa, 

 near Savona. The second shock was slight. The third was 

 strong, but short. 



The noise before the first shock was very loud, like a large 

 steam blast. There were more than half a dozen other shocks 

 in the two following days, but they were slighter, and chiefly 

 oscillatory ; curiously enough, we did not mind them so much 

 as the vibrations, though I believe they are much more dangerous, 

 if severe. 



The night before the earthquake some horses were nervous 

 and refused food, and dogs howled, but I naturally supposed that 

 it had something to do with the Carnival which was being 

 celebrated at the time. J. E. H. Peyton. 



108 Marina, St. Leonards-on-Sea, May 19. 



The Shadovir of Adam's Peak. 



I HAVE recently seen a paper, read before the Physical Society 

 by the Hon. Ralph Abercromby, which apparently shatters an 

 explanation proposed by me to the same Society of the pheno- 

 mena of the shadow of Adam's Peak in Ceylon. Whilst not 

 anxious to support my own theory, if one more consistent with 

 the phenomena has been discovered, I venture to think that 

 there are certain considerations which militate against the new 

 theory, and render it incomplete ; and, with your permission, I 

 will enumerate them. 



(i) Mr. Abercromby says that it is the intervention of near 

 and moving mist which produces the apparent uprising of the 

 shadow. Is it possible that such a simple explanation could 

 have escaped the notice of the hundreds of observers who have 

 witnessed the phenomenon, and returned with the impression 

 that there was something inexplicable about the shadow ? It is 

 difficult to imagine observing and reasoning faculties so rudi- 

 mentary as not to be able to observe that a shadow was on mist, 

 and reason from that to an explanation of the apparent approach 

 and uprising of the shadow. 



(2) Mr. Abercromby's theory depends on the intervention of 

 • near and moving mist rising from the Maskeliya Valley. This 

 valley stretches away behind the observer in a south-east direc- 

 tion as well as to the north-west, and mist rising from it would 

 be quite as likely to intercept the sun's rays behind as to form a 

 curtain in front for the shadow to be projected on, and it would 



be only on very rare occasions, such as Mr. Abercromby de- 

 scribes, that the mist would keep entirely to the north-west of 

 the Peak. Why it should do so is not explained. Therefore 

 the uprising of the shadow could only be seen on such very rare 

 occasions. 



(3) Mr. Abercromby says : " Our fortune was in the unsettled 

 weather, which made the mist so coarse and close that the 

 unequivocal bow left no doubt as to the true nature of the cause ; " 

 "the sky was covered with a confused mass of nearly every 

 variety of cloud ; " " below and around us cumulus and mist ; " 

 " a pale moon with an ill-defined corona ; " " sometimes masses 

 of mist coming up from the valley enveloped us with condensed 

 vapour;" "driving condensed vapour was floating about, and 

 a fragment of rainbow-tinted mist appeared near the top of the 

 shadow." Under such conditions, what else could Mr. Aber- 

 cromby have seen than what he describes, the shadow on the 

 mist, a circular i-ainbow, spectral figures like those of the Brocken, 

 the rising and falling of the shadow as the mist intervened or 

 passed away ? Instead of " fortunate " in his conditions, I think 

 Mr. Abercromby was the very reverse. To be "fortunate" he 

 should also have seen the shadow in a clear atmosphere, and 

 noted the absence of any appearance of uprising. Mr. Whymper, 

 in his famous descent of the Matterhorn after the accident, saw 

 in the evening a fog-bow very similar to that described by Mr. 

 Abercromby, and the presence of mist was noticed in that case. 

 But I ask, and I am willing to rest my theory on the answer, Is 

 not the phenomenon of the apparent uprising of the shadow, 

 witnessed when no mist is visible, and the atmosphere to the 

 north-west is clear ? This furnishes a simple crux of the two 

 theories ; for any observer can notice whether mist is visible or 

 not, and if not, whether there is any appearance of the uprising 

 of the shadow or not. Until corrected by future observers, I 

 maintain that the phenomenon is seen when there are not 

 "around us cumulus and mist " and "masses of mist coming 

 up from the valley ; " in fact, when the air is so calm and clear 

 that the coast-line can be traced at a distance of seventy miles or 

 more. If I am proved to be correct in this opinion, the new 

 theory has not advanced the explanation by a single step. My 

 theory of total internal reflection depends on the difference of 

 temperature between the air in the low country and on the Peak, 

 which is most marked in clear calm weather, ice forming at 

 such times on the Peak, while a fall of the thermometer to 70° F. 

 in the low country is commented on as noteworthy by the news- 

 papers. The conditions described by Mr. Abercromby render 

 the idea of mirage absurd ; but they also suggest, if the new 

 theory be correct, the absurdity of there ever having been any 

 mystery about the phenomena of the Shadow of the Peak. 



May 30. R. Abbay. 



Upper Wind Currents near the Equator and the 

 Diffusion of Krakatab Dust. 



I REGRET that Mr. Abercromby, before writing his interesting 

 and suggestive article under the above heading, had no oppor- 

 tunity of making himself acquainted with the conclusions 

 arrived at by the Krakatab Committee regarding the rate at 

 which the finest ejecta were carried round the world. The 

 velocity he ascribes to the material, viz. 120 miles an hour, 

 deduced apparently from the few observations he quotes, is 

 quite 40 miles an hour in excess of that deduced from the 

 numerous cases treated by Mr. Russell and myself. In one or two 

 cases in the Indian Ocean the velocity does apparently approach 

 to that given by Mr. Abercromby, but these are both exceptional 

 and doubtful, since they were probably due to minor outbursts 

 antecedent to that which gave rise to the grand stream which 

 encircled the globe at an average pace of 80 miles an hour. 



Mr. Abercromby has thus accidentally made the problem 

 appear far more formidable than it really is. A constant velocity 

 of 120 miles an hour right round the world, though not outrageous 

 to anyone who reflects on the great mobility of the atmosphere at 

 the height of 100,000 feet or more, certainly makes a consider- 

 able demand upon our powers of scientific imagination, while a 

 velocity of only 80 miles an hour, even though constant over 

 the entire equatorial belt, does not appear, at such a height, to 

 be opposed to what is already known of the motions of the 

 atmosphere at the far inferior elevation of the cirrus clouds. 



The height of the stratum is certainly a factor which cannot 

 be overlooked, for if we find the average velocity of the wind 

 continually increase as we ascend to the cirrus, it is reasonable 

 to conclude that it rises beyond this limit, and if so a constant 



