208 Mr. Waldie's investigations connected [No. 3, 



Influence of the Tides. 

 It will indeed be convenient to take up this subject first in order. 

 Dr. Macnamara's results exhibit very clearly the increased quantity of 

 saline constituents during the hot season, commencing in March, and 

 coming to its height just before the commencement of the rains. His 

 table shews as much as 77.7 grs. dry saline residue from 1 gallon of 

 water at high water on 12th June, 1862. I obtained from water taken at 

 full spring tide, on 14th June of this year 1866, as much as 106.3 grs. 

 per Imp. gallon. This is easily accounted for when it is found, as ascertain- 

 ed from examination of the rainfall, that from June 1861 to end of May 

 1862 there had fallen 87.4 inches of rain, while during the correspond- 

 ing period of 1865-66 there had been only 47.9 inches : the river 

 must have "been much lower and its current feebler, and consequently 

 the sea w T ater had penetrated farther. My observations were all made on 

 water taken from the river near my own residence at the village of 

 Baranagur or Barnagore, with a few exceptions which I shall notice 

 afterwards. The locality is about two miles above Cossipore. But I 

 made observations also on the effect of time of tide. 



This point is also noticed in Dr. Macnamara's report, though not 

 very fully. He mentions that the water varies much in the degree of 

 its impurity with the time of tide, falling as low during April and May 

 as 23° at low water, that is, 23 grains of saline matter in 1 gallon. My 

 observations indicate even a greater amount of variation than is by this 

 suggested, as will be shown by the table I have prepared. As the 

 evaporation to dryness and weighing the residue of numerous samples is 

 very tedious and troublesome, another plan was adopted for estimating 

 the amount of variation. The river water proper contains very little 

 chlorine in its composition, while in the state of common salt this is 

 the characteristic constituent of sea water. The quantity of chlorine 

 was therefore ascertained by the usual volumetric process with nitrate 

 of silver, and calculated as if it existed entirely as chloride of sodium 

 or common salt, which afforded a very good means of comparing the 

 samples and estimating the proportion of sea water present. 



I endeavoured to make some observations further up the river, but 



found that it could not be done properly except with an expenditure 



of time, trouble, &c. that I could not devote to it. Any observations 



that I did make were only confirmatory of Dr. Macnamara's results. 



The following table exhibits the results of my observations on the 



! 



