1878.] Ohi^ervatiom in the Gulf of Ciiicli. 41 



tion of the wind, and the amount of rainfall ; and it is believed that no series 

 of tidal observations has been better furnished than these with the requisite 

 data for separating local atmospheric influences from the true tidal con- 

 stituents, which are caused by the varying position of the sun and moon. 



Sjyir it -leveling operations. — At short distances round each station 

 three blocks of stone were sunk in the ground to serve as bench-marks for 

 future reference, and each of them was carefully connected with the zero of 

 the tide-guage. Bench-marks were also placed in position, one at about 

 every 10 miles, from Okha station along the road to Hanstal and thence to 

 Nawanar in Kutch across the Kunn. Bench-marks were also laid down with 

 reference to the nearest Great Trigonometrical Stations. During the field- 

 season of 1874-75, Capt. Baird conducted a series of spirit-leveling operations 

 for determining the present relative levels of the datum points of the three 

 tidal stations, and of the stone bench-marks which had been laid down a 

 year previously along the lines to be levelled over. The length of the main 

 lines connecting the three tidal stations was 275 miles, which was leveled 

 over independently by Capt. Baird and Narsing Dass, in accordance with 

 the rigorous system which has obtained for several years past in the G. T. 

 Survey. 29 miles of branch lines were also executed, in order to connect the 

 stations of the Kattywar triangulation with the tidal stations. 



In working between Nawanar and Hanstal, Capt. Baird had to make 

 a considerable detour round the head of the Gulf, crossing the Runn be- 

 tween Shikarpur and Mallia. Several bench-marks were fixed on the Runn, 

 and they will be important points of reference when these operations are 

 repeated with the tidal observations some years hence, when a sufficient in- 

 terval shall have elapsed to allow of the rising or sinking of the surface of 

 the ground to an appreciable extent. The existing surface-level of the 

 Runn has been obtained at a number of points, for Capt. Baird took the 

 precaution of having all the pins on which the leveling staves were set up, 

 driven downwards until their heads were exactly flush with the surface of 

 the ground. 



Operations during the Monsoon. — Considerable anxiety was felt as to 

 the possibility of securing continuous records during the monsoon, when 

 heavy gales are prevalent ; but every precaution was taken to strengthen 

 the wooden observatories in which the instruments were set up, and to 

 anticipate and provide for all possible contingencies ; and it was most satis- 

 factory that, although the monsoon of 1874 set in very severely and lasted 

 long, the observatories all stood firm, and the tide-gauges and other self- 

 registering instruments remained in good working order throughout the 

 season. 



Close of the Operations. — The carrying out of the periodical inspections 

 during the monsoon was the most trying and difficult part of the operations. 

 



