696 report— 1878. 



stated as that which enters the river every tide, we have 14,024,048,220 cubic feet 

 as the mean quantity of sea water which enters the Thames every tide. 



It is difficult to form a true idea of the relative values of such large numbers, 

 and therefore it is better to reduce them to a percentage, when we obtain the result, 

 that the mean composition of the Thames water is as follows, namely : — 



Sea water 98-91 



River water 102 



Sewage water -07 



10000 

 That is to say, the actual mean quantity of sewage in the tidal portion of the 

 river Thames, extending from Teddington to Yantlet Creek, is only - 07 per cent., 

 or otherwise expressed, only one 1477th part of its whole bulk. 



Furthermore, it must be borne in mind that, owing to the circumstance of the 

 river water always being delivered at the upper end of the elongated reservoir, no 

 less than 60 miles in length, while the ultimate discharge is wholly from the lower 

 extremity, the composition of the water varies greatly, being always much freer 

 from sea water and sewage in the upper portion than the lower. In point of fact, 

 it must be evident that, in the case of a stream which has a certain quantity of 

 river water, that is, as we have already defined it, water derived from the rainfall 

 and discharged into the river by surface drainage and land springs, there must 

 always be a point, even in the tidal portion, above which no contamination can 

 exist from sea water or other matters which enter the river near the lower portion 

 of its course. 



The foregoing is a statement of the average result ; the actual amount of con- 

 tamination by sewage at any given time and place must depend upon the recent past 

 rainfall, and upon the state and condition of the tides, but at no time, and under 

 no circumstances, can the amount of the sewage contained in the Thames water be 

 raised sufficiently above its average value of one 1477th part to produce any ap- 

 preciable pollution, far less to afford any ground for the statements to which pre- 

 vious allusion has been made. 



3. Recent Improvements in the Port of Dublin. By B. B. Stoney. 



This communication was ordered by the General Committee to be printed 

 in extenso among the Reports. — See above, p. 167. 



