TIDAL AND LEVELLING OBSERVATIONS. 201 



During 1878 the gauges continued to work well, though at 

 Madras and Vizagapatam the occurrence of cyclones caused damage 

 to the apparatus, and temporarily interrupted the observations. 

 Sites for future sites, chiefly along the Arakan and Tenasserim 

 coasts, were selected, and progress was made with the lines of 

 spirit-levels, chiefly in the Bombay Presidency. In the following 

 year six additional places for the erection of tidal gauges were 

 selected, viz., False Point, Rangoon, Elephant Point, Amherst, 

 Moulmein, and Port Blair, at which place the clerk in charge was 

 a licensed European convict who was also the port signaller. Self- 

 registering anemometers, and aneroid barometers, and verificatory 

 mercurial barometers were erected at all the tidal stations, with the 

 exception of Karachi, Bombay, and Madras ; at the last two of 

 which there were meteorological observatories already in existence. 



The accuracy of the tidal registrations depends very greatly on 

 the adjustment of the instrument both to true time and to a 

 definitely fixed level, so that when the pencil in traversing the paper 

 on the barrel crosses an hour-line the time should be exactly that 

 of the hour indicated, and when it crosses a height line the height 

 should be exactly that of the momentary height of the sea-level 

 with reference to the bed-plate of the instrument or any fixed 

 bench mark in its neighbourhood. The several adjustments and 

 settings are of course made with great accuracy before the com- 

 mencement of the registrations, but this would be of little use if 

 the instruments were not maintained uniformly in exact adjustment 

 throughout the entire period of registration. Fortunately, there 

 was a telegraph office at nearly every place where a tidal observatory 

 had been established, so arrangements were made to correct the 

 clocks of the self -registering instruments to local time wherever 

 necessary by communicating with the adjoining telegraph office. 

 In 1880-81 the number of self-registering tidal gauges was 14, 

 while new stations were being erected at Kidderpore, Diamond 

 harbour, Saugor island, Bhaunagar, and Negapatam. 



A complete set of all the instruments used in connexion with the 

 tidal operations on Indian coasts was sent for exhibition to the 

 Geographical Congress at Venice. The tide gauge was connected 

 with the Grand Canal, and registered the tides there during the 

 duration of the exhibition. Captain Baird was awarded a gold 

 medal of the first class in acknowledgment of his scientific services 

 in regard to tidal matters. 



