1832.] Temperature and Saltness of the River HugU. 107 



preserves a temperature above 80° throughout the year, sometimes 

 reaching 85° and 86 u . I found the surface of the sea off Point de Galle 

 83° on the 22nd December, and 90° in May ; the mean of these is far 

 above the medium temperature of the climate. Other examples I 

 could cite to the same purport. The rivers of Mexico and the Orinoco 

 reach the temperature of 90 when the temperature of the air is much 

 below that degree. 



The second table exhibits the specific gravity of the river water 

 at four places, from actual observations made at different seasons. 

 There will appear some discordance among them, from the accident 

 of my passing places at different states of the tide, and consequently 

 not obtaining the maxima and minima at each place on the same 

 trip. To obtain any thing like exactness in ascertaining the saltness 

 of the river in each month of the year, it is obvious, that daily ob- 

 servations should be taken for a long period at many stations and 

 at every change of the tide. There is great inequality of season in this 

 particular: on the 31st October 1830, the specific gravity off Mud 

 Point was 1006.5 at high water spring tide ; whereas, in 1831, so late 

 as the 6th November, it was but 1001. at the top of the springs. 

 But, although the observations I have collected are not sufficiently 

 numerous to afford an accurate mean for each or perhaps any one point 

 on the river, they may be employed to form a table of the whole by 

 estimate. To ascertain the influence both of the tides and of the freshes, 

 — the latter at one season pushing the sea water quite out of the river 

 channel, upon which in the other season it constantly encroaches, until 

 the water at Mud Point becomes almost as briny as at the Sand 

 Heads, and a slight degree of saltness is perceptible even at Calcutta, — 

 I drew out a table of distances from Calcutta, and inserted in columns 

 for every month (repeated for each year of observation) all the observations 

 of high and low water, with a few others when those were deficient. This 

 would be much too confused and voluminous for your pages ; but it has 

 enabled me to prepare the following (third) table, which, although 

 formed by estimate, and not by actual averages, is not likely to be very 

 wide of the truth : indeed, I scarcely think the errors exceed .001 in any 

 place. The zero, at the head of each column, represents the point at 

 which saltness ceases to be perceptible at high and low water spring- 

 tides. It will be seen, that the sea water gains a little in September 

 when the freshes are the strongest ; this is owing to the great rise of 

 the equinoxial tides, which in the autumn are much higher than those 

 of March, the average level of the sea being 3 to 4 feet higher in 

 September, than it is at the end of the north-east monsoon. 



p 2 



