122 CEYLON PEAKL OYSTER REPORT. 



OBSERVATIONS ON THE SEA AROUND CEYLON, AND ESPECIALLY 



IN THE GULF OF MANAAR. 



Although we were not prepared to make detailed physical observations on the sea- 

 water, as I had not considered that necessary for our purpose, we kept a daily record 

 of such approximate temperatures and densities as we could obtain with ordinary 

 laboratory thermometers and hydrometers, sufficient to enable us to compare localities 

 and seasons. During the cruises of the " Lady Havelock" the temperature and specific 

 gravity were taken twice daily, in the morning after we had started the dredging 

 operations generally at 7 a.m. and in the evening when work was finished, about 

 7 p.m. After I left, Mr. Hornell continued the records at Galle, and on occasions 

 at Trincomalee and in the Gulf of Manaar, and took the observations once daily, 

 between 8 and 10 in the morning, generally at 8.30. We also took all opportunities 

 of making such observations as were possible on the surface drift of the sea, and 

 obtained such information as we could as to prevailing currents at different seasons, 

 as these movements of the water must be of great importance in connection with the 

 distribution of the young pearl oysters. 



During the period (January to April, 1902) of the two cruises in the "Lady 

 Havelock " and our first inspection of the pearl banks, the sea temperature was 

 steadily rising. At the beginning of the time, in the Gulf of Manaar, it was about 

 77 F, in February it averaged 79 F., in March 84 F, and in April 86 F. The 

 specific gravity was nearly constant at l - 0230 in the Gulf of Manaar, while at 

 Trincomalee, in February, it was lower varying from 1*017 to l - 020. 



In July, 1902, the sea temperature at Galle ran up to 86 F., and the specific 

 gravity was constant at l - 0236. Mr. Hornell found that the temperature of the 

 water in our shaded aquarium tanks was considerably lower (say 3 F.) than that of 

 the sea outside. 



In August the temperature of the water in our aquarium reservoir, taken at 8 a.m., 

 ranged from 78 F. to 82 F., the average being 80-37 F 



In September the temperatures were taken in the open water at the jetty and 

 ranged from 81-5 F to 85 F., and the specific gravity from 1-0216 to 1'0220. 



In October the temperature at Galle jetty fell from 86 F. to 82 -5 F. ; at Trin- 

 comalee the range was 84 F. to 89-5 F, and in Tamblegam Lake 87 F. to 90 F. 



In November Mr. Hornell was again on the pearl banks and found that the sea 

 temperatures ranged from 83 F. to 85 F., and the specific gravity from T0200 to 

 T0227. At Galle jetty at the end of the month the sea temperature was 85 F. 



In December, at Galle jetty, the sea temperature was nearly always at 84 - 5 F., 

 the extremes in range being only 8 3 "5 F. and 85 F. 



In January, 1903, at Galle jetty, the range was from 82 F. to 84^ F., and the 



