1873.] D. WMie— On the Muddy Water of tie Rugli. 217 



will settle readily b}^ repose. If the suspended matter in such waters con- 

 sist partly or chiefly of carbonate of lime, how it will be affected by the 

 soluble salts present I am not prepared to say, as I have had no opportunity 

 of examining such waters. A French author, whom I shall quote presently, 

 speaks of waters which are never clarified cntirel}' by repose ; such are, as 

 he calls them, " les eaux hlanclies de Versailles,'' which owe their milky tint 

 to their contact with layers of calcareous marl. Whether these waters 

 contain soluble salts of lime or not, I do not know. 



In a note to the chapter referred to, Bisclioff mentions that Th. Scheerer* 

 had found that " the deposition of suspended matter is hastened when cer- 

 " tain salts — alum, sulphates of copper and iron — are dissolved in the water. 

 " But since a solution of chloride of sodium behaves like pure water, it can- 

 " not be expected that the suspended matter is deposited more quickly in 

 " the sea than in rivers." Now here is a mistake, for solution of chloride 

 of sodium does not behave like pure water. Mr. Skey, more correctly, thinks 

 that the transparenc}^ of the sea may depend on the precipitation of mud by 

 the saline matter. Scheerer's observations must I think have been too has- 

 tily or imperfectly made. 



The French works just referred to,f very valuable no doubt for what 

 they were intended, principally engineering, did not, however, contain much 

 of the sort of information I was in search of. That by Darcy gave me some 

 worth noticing. It contains accounts of the filtering operations at Chelsea, 

 Southwark, Thames Ditton, York, Hull, Paisley, Glasgow and Marseilles, 

 also of the natural filters of Nottingham, Perth, Toulouse and Lyons. The 

 natural filters are out of the range of the present enquiry, the first four ap- 

 pear to be on a similar plan to those at Palta, the latter three are different 

 in their arrangements for cleaning the sand. Those of Grorbals, Glasgow, are 

 not sufficiently well described, those of Paisley are ; in both the clearing is 

 effected by passing the water from below upwards, but, as the nature of 

 the water is not at all likely to have any analogy with the water under 

 consideration, I need not notice them. The filters at Marseilles, however, are 

 worthy of a little attention. The water which supplies Marseilles is derived 

 from the Durance. This water, as well as that of the Khone, judging from 

 the description, must have a considerable similai-ity to that of the Hugli 

 during the rains, at least during certain periods, requiring a long time to 

 settle and become clear. From some things stated in the account of the 

 filtering operations, however, I do not think that the particles of the sus- 



* In Poggendorflrs Annalen, Vol. 82, p 419, date unknown but previous to 1854. 



t Traite de la conduite et la disti'ibution des eaux, par J Dupuit, Paris, 1854 and 

 Les Fontaines publiques de la ville de Dijon par Henry Darcy, Puris, 1856, both 

 beautifully illustrated by plates. For inspection of these I have to thank Dr' 

 Tonnerre, Health Officer to the Municipality. 



