1884.] Tidal Disturbances caused by Eruptions at Java. 249 



some years past it has been Major Baird's special duty, as an officer 

 of the Great Trigonometrical Survey of India, to supervise the 

 operations for the investigation of tidal phenomena which have been 

 carried on under the orders of the Government at a number of points 

 on the Indian coast lines from Kurrachee round to Moulmein, and 

 also at Aden. A tidal observatory, containing a self-registering tide- 

 gauge, and all the necessary meteorological instruments, has been 

 established at each of these points ; every observatory has a man in 

 charge who tends the instruments, sets the diagrams to true time as 

 received telegraphically from Madras, and submits daily reports to 

 Major Baird. 



After the occurrence of the eruptions at Krakatoa, Major Baird 

 made a careful examination of the diagrams at the whole of his tidal 

 stations, seventeen in number, and at twelve of them he found more 

 or less distinct evidence of tidal disturbance. In the accompanying 

 report he sets forth this evidence, and gives such further facts as he 

 has been able to collect from information supplied by eye-witnesses 

 of the disturbances on the coasts of Ceylon and at other localities 

 where as yet tidal stations have not been established. He also gives 

 the magnitudes of the " supertidal " waves and the intervals between 

 them ; shows by calculation the probable time of the great eruption 

 at Krakatoa ; and then deduces the velocities of the waves which 

 reached each station. He furnishes copies, on a much reduced scale, 

 of the original diagrams of the tidal registrations of the 27th and 

 28th August which were made at each of his own stations ; and he 

 also gives a chart of a portion of the Indian Ocean which he has 

 prepared to illustrate the course of the first great supertidal wave. 



The testimoiiy of the diagrams of self-registering tide-gauges must 

 ordinarily be expected to be much more precise and reliable than that 

 of eye-witnesses. This may be more particularly claimed in the 

 present instance ; for the clocks of the gauges were carefully super- 

 vised, and their times checked daily, at every station but Port Blair, 

 by Madras time signals, and the diagrams are on so large a scale, 

 60 inches in length by 24 in breadth, that any sensible variation of 

 sea-level is measurable on them ; for it is depicted on the full natural 

 scale wherever the tide range does not exceed 5 feet, and on half 

 that scale where the range exceeds 5 but does not exceed 10 feet, the 

 corresponding time scale being in all cases 1 inch to an hour ; and as 

 the stations at which the range of tide is less than 10 feet happen 

 to be those at which the disturbances were greatest, very exact 

 measures of the times and amplitudes of all the supertidal waves, 

 whether small or great, are forthcoming for all the more important 

 stations. The diagrams accompanying Major Baird's report were 

 intended for illustration rather than for measurement ; thus they have 

 all been drawn on a much smaller scale than any of the originals, 



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