358 



NATURE 



[Feb. 14, il 



bright and clear and distinclly iridescent. Around the head of 

 the figure was a beautiful halo of light, and from the figure itself 

 shot rays of colour normal to the body. The sight startled me 

 more than I can now tell. I threw up my hands in astonish- 

 ment, and perhaps .«ome little fear, and at this moment the 

 spectre seemed to move towards me. In a few moments I got 

 over my fright, and then, after the figure had faded away, I re- 

 cogni-ed the fact that I had enjoyed one of the most wonderful 

 ]>henomena of nature. Since then we have seen it once or twice 

 troni Jeff Davis Peal;, but it never created such an impres-ion upon 

 me as it did that evening when I was doing service as a heliotropcr 

 all alone on the top of Arc Dome." 



The Stjrm of January 26 



During this storm there was a remarkable depression of the 

 barometer, it falling to 26'9, as shown in the accompanying 

 chart. The lowest depression last year was 2S'2 on Nov. 25. 

 Lurgyhrack lies in lat. 54" 56' N., and long. 7° 42' W. It is 225 

 feet above the Ordnance datum level. A nearly similar depres- 



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niwi 

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sion was"observe( :he Ordnance 



datum level. TI... „ .^^.^„ .„„..„ ^ .lorth-west Ijy 



north and east to the south, and from llie latter by west to 

 north. The storm was succeeded by a fall of snow, which has 

 now melted away. G. Henry Kinahan 



I.urgyhrack, Letterkenny, Ireland, January 29 



EARTHQUAKE DISTURBANCES OF THE 

 TIDES ON THE COASTS OF INDIA 

 TipCR some years past tidal stations have been esta- 

 -'■ blished at various points on the coasts of India, 

 from Kiirrachee round Ha Cape Comorin and yVdam's 

 Straits to Calcutta, and on to Rangoon and Moulmein ; 

 also beyond these points, eastwards at Port Blair in the 



Andaman Islands, and westwards at Aden ; but not any- 

 where in the Island of Ceylon, which happens — unfortu- 

 nately for the interests of science— to be outside the 

 administration of the Government of India. At each of 

 the tidal stations an ob-ervatory has been established, 

 containing a self-registering tide-gauge, and all requisite 

 meteorological instruments, with a clerk in charge who 

 tends the instruments, sets the driving clocks to true 

 time — usually received telegraphically from Madras — and 

 sends in daily reports to the supervising officer. That 

 officer exercises a general superintendence over all the 

 tidal stations, inspects them periodically, collates and 

 analyses the observations, and deduces from them the 

 values of the ''tidal constants'' for each port or point of 

 observation ; these constants enable future tides to be 

 predicted, and tide tables to be prepared for the guidance 

 of mariners ; they are also otherwise valuable, in that they 

 have thrown light on the question of the earth's rigidity, 

 and on various other matters of scientific interest. 



The operations have been carried on in connection 

 with the Great Trigonometrical branch of the Survey of 

 India. Major A. W. Baird, R. E., has been the super- 

 vising officer from their commencement in 1873 up to the 

 present time, with the exception of an interval of a little 

 more than a year, when he was on furlough in Europe, 

 and Capt. J. Hill, R.E., first, and afterwards Major 

 M. W. Rogers, R.E., officiated for him. 



At certain of the Indian stations the registrations have 

 twice indicated that the normal tides had been greatly 

 disturbed by supertidal waves : first, on the occasion of 

 the earthquake in the Bay of Bengal on December 31, 

 iSSi ; and secondly, during the volcanic eruptions in the 

 Island of Krakatoa, between .Sumatra and Java, which 

 occurred on August 27 and 28 last. The first disturb- 

 ances do not appear as yet to have attracted much atten- 

 tion out of India ; a full account of them is given in the 

 General Report on the Operations of the Survey of India 

 for 1881-82, and also in the Proceedings of ike Asiatic 

 Society of BengaMm March 1883. The second are now 

 famous all the world over, not merely because of the 

 havoc they are known to have produced on the spot and 

 at the time, but also because of the effects they are 

 believed to have produced on the condition of the atmo- 

 sphere long afterwards and in far distant quarters of the 

 globe. A report on the tidal disturbances at Indian 

 stations which were caused by the eruptions at Krakatoa 

 has been drawn up by Major Baird, and sent to me for 

 communication to the Royal Society, and an abstract 

 of it was read at the meeting of the Societv on January 

 31- 



I now propose to indicate certain points of similarity 

 and others of dissimilarity between the recorded effects 

 of the disturbing forces on the two occasions; for fuller 

 details the reports themselves must be referred to. 



The usual effect of an earthquake or volcanic eruption 

 occurring at an island or under the bed of the sea is the 

 transmission in all directions of an " earth-wave " and a 

 "sea-wave"'; the former travels with much greater 

 rapidity than the latter, and may reach points which the 

 latter does not reach ; or it may die away and cease at 

 points far short of those attained by the latter ; which of 

 the two will travel the greater distance depends generally 

 on the structure and homogeneity of the strata through 

 which the earth-wave is transmitted, and on the depth of 

 water and configuration of the bottom over which the 

 sea-wave passes. 



On the occasion of the earthquake of December 31, 

 1881, the "centre of impulse" was situated under the 

 bed of the ocean in the western portion of the Bay of 

 Bengal ; the shock of the earth-wave was very violent in 

 the Andaman and Nicobar Islands, and along the entire 

 length of the Madras coast up to Calcutta, and also far 

 inland ; it was followed by a succession of sea-waves 

 which the tidal diagrams show to have arrived after the 



