68o Memoirs of the Indian Museum. |Voi<. V, 



based entirely upon observations made on the surface waters, and it was felt that 

 this was not altogether satisfactory. I therefore undertook to carry out a series of 

 observations on the water at different levels, but as in the time at my disposal it 

 would have been quite impossible to conduct such a hydrographie survey of the 

 whole lake, I decided to confine my investigations to a small area, and Rambha 

 Bay at the extreme south end was selected as being the most convenient locality. 



The water-samples were taken by means of an ' Ekman ' reversing water-bottle 

 and temperatures were simultaneously recorded by a reversing thermometer and 

 were subsequently reduced in accordance with the formula given by W. Walfrid 

 Ekman. L The density of the water-samples was estimated — usually on the day follow- 

 ing their collection — by a f Buchanan ' hydrometer and the findings were subsequent- 

 ly reduced to o°C, Standard Temperature, and temperature in situ by means of 

 Knudsen's Tables. I have throughout adopted 250°C as Standard Temperature, 

 so that my results are not directly comparable with those given by Annandale and 

 Kemp who reduced their results to i5°C.* 



The various stations — numbered consecutively — were made as nearly as possible 

 in lines, running roughly at right angles to the main length of the bay and more or 

 less parallel with each other, so that the results obtained could be plotted out in 

 sections. The positions of the stations were in every case taken by means of a pris- 

 matic compass, and, in order to fix them as accurately as possible, three observations 

 were taken at each station of the bearings of prominent land-marks ; their positions 

 are shown in Chart i. 



The results obtained by Dr. N. Annandale and Dr. S. W. Kemp in 1914 showed 

 very clearly that there was during the course of that year a very considerable range 

 of variation in the degree of salinity of the surface water, correlated with and in the 

 main due to two causes, namely, the influx of fresh water from the Mahanaddi River 

 system during the S.W. monsoon season and the influx of sea-water during the 

 winter months. To quote their own words [loc. cit., pp. 11-12), the conclusions at 

 which they arrived were that "the annual sequence of events, as it concerns the lake 

 as a whole, may be stated briefly as follows : — 



' The floods that enter the lake at the close of the monsoon from the Mahanaddi 

 delta expel all salt water from the northern portion, driving it through the outer 

 channel to the sea, and are of sufficient volume to raise the level of the lake some 5 

 or 6 feet above the mean of the dry season. There being no outlet at the southern 

 end, the comparatively saline water which had accumulated there is banked up by 

 the flood, becoming, however, diluted to a considerable extent both by admixture 

 with water from the north and by surface drainage from the land in the vicinity. 

 Towards the end of the year the floods subside. The first effect of the alteration in 



1 W. Walfrid Ekman: "On the use of insulated water-bottles and reversing thermometers," 

 Pub. de Circonstance, No. 23. {Conseil permanent Internat, pour l'explor. de la mer. Copenhagen, 

 April, [905.) 



2 Table IV (p. 710) shows the corresponding values of the different densities at 25°C and I5°C 

 respectively. 



