204 TIDAL AND LEVELLING OBSERVATIONS. 



at Madras in 1881 was about one foot lower relatively to the land 

 than it was 60 years previously. 



In connexion with the subject of tidal observations mention 

 should be made of the earthquake which happened on the morning 

 of the 31st December 1881 in the Bay of Bengal. It was very 

 violent in the neighbourhood of the Andaman and Nicobar islands, 

 more or less violent along the entire length of the west coast from 

 Ceylon to Calcutta, and slight at various points along the east coast. 

 The earth-waves appear to have lasted for only a few seconds, but 

 the ocean was greatly disturbed, and the waves continued to roll 

 against the east coast for several hours afterwards. At Rangoon, 

 Moulmein, and Amherst there was no disturbance of river and 

 ocean surface, but at the island of Kisseraing, below Tenasserim, 

 Major Rogers, who was at the very moment measuring angles with 

 one of the great theodolites, " saw the earthquake before feeling it," 

 as the signal which he was observing (some 15 miles distant) 

 appeared to rise and fall in the field of the telescope. On looking 

 at the levels of the instrument he found that they were violently 

 agitated, and he subsequently ascertained that the earthquake had 

 been felt, at almost the same moment, at Madras and False Point, 

 on the opposite coast. The origin or centre of impulse was there- 

 fore, in all probability, a point in the bay almost equi-distant from 

 the three stations, but lying a little to the south.* 



During 18S2-S3 the Paumben observatory ceased to be operative, 

 owing partly to .severe weather and partly to the observatory and 

 equipment being more needed in Ceylon ; and those at Karwar and 

 Elephant Point were also dismantled. In all 18 groups of 

 observations were reduced, and the so-called " constants " supplied 

 to Mr. E. Roberts for computation of prediction tables by the tide- 

 calculating machine. 



These tide gauges afforded an unique opportunity of observing the 

 tidal phenomena resulting from the great eruption of Krakatoa, in 

 Java, on the 27th and 28th August. Major Baird prepared a full 

 report on the subject, dated December 1883. His main conclusions 

 are : — 



1. The primary effect of the eruption was a marked fall in the 

 sea-level, or. in other words, the formation of a negative 

 super-tidal wave at each of his stations. 



* Major M. W. Roger's report is printed at page 71 of the Appendix to the Indian 

 Survey Report for 1881-82. 



