72 Dr. Edward FranMand [Feb. 21, 



The annual rainfall of the district is estimated on an average at 

 28 inches. The rivulets and streams of the Thames basin are formed 

 and pursue their course on the clay land. There are no streams on 

 the chalk. That which falls upon this porous stratum and does not 

 evaporate, sinks, mostly where it alights, and heaps itself up in the 

 water-bearing stratum below, until the latter can hold no more. The 

 water then escapes as springs at the lowest available points. Innu- 

 merable examples of these springs occur all round the edge of the 

 Thames basin, and at various points within it. Thus, from the chalk 

 they are ejected at the lip of the gault, and in the oolitic area, by 

 the fuller's earth below it, or by the Oxford clay geologically above it. 

 According to the gaugings of the engineer of the Thames 

 Conservancy Board there passed over Teddington Weir in 1892, 

 387,000 millions of gallons, equal to an average flow of 1060 millions 

 of gallons daily. In the following year, 1893, there passed over 

 Teddington Weir an aggregate of 324,227 millions of gallons, or a 

 daily average of 888 millions of gallons, the average for the two years 

 being 974 millions of gallous ; and this number does not include the 

 120, or 130, millions of gallons daily abstracted by the six London 

 water companies who draw their supplies, wholly or partially, from 

 the Thames. 



Thus, in round numbers, we may say that after the present wants 

 of London have been supplied from this river, there is a daily average 

 of a thousand millions of gallons to spare. Surely it is not too 

 violent an assumption to make, that the enterimsing engineers of 

 this country can find the means of abstracting and storing, for the 

 necessary time, one-fourth of this volume. 



As regards the quality of ihis stored water, all my examinations 

 of the effect of storage upon the chemical, and especially upon the 

 bacterial quality, point to the conclusion that it would be excellent. 

 Indeed, the bacterial improvement of river water by storage, for 

 even a few days, is beyond all expectation, as is proved by the ac- 

 companying photographic diagrams. Thus the storage of Thames 

 water by the Chelsea company for only thirteen days, reduces the 

 number of microbes to less than one-eighth of the original amount, 

 as is proved by the photographic diagrams. Figs. 17 and 18. Fig. 17 

 shows the result of a gelatine plate culture of -}q of a cubic centi- 

 metre of unfiltered Thames water collected on January 10, 1896. 

 It gave 11,560 colonies per c.c. ; whilst Fig. 18 shows the result of 

 a similar cultivation of ^L of a c.c. of Thames water collected on the 

 same day, after storage for thirteen days. It gave only 1360 colonies 

 per c.c. The storage of the Eiver Lea water for fifteen days, by the 

 East London company, reduces the number from 9240 to 1860 per 

 c.c, or to one-fifth (see diagrams Figs. 19 and 20) ; and lastly, the 

 water of the New River Cut, containing on the average 4270 microbes 

 per c.c, contained after storage for less than five days only 1810 (see 

 diagrams, Figs. 21 and 22, in which the results of the cultivation of 

 Jq of a c.c. of the water before and after storage are contrasted). 



