4.2: 



NA TURE 



[August 29, 1901 



the extent of their original pollution and the length of 

 their uncontaminated flow; and the impurities in sus- 

 pension may to a considerable extent be removed by 

 causing the water to remain at rest in a settling basin 

 for a certain period before distribution, so that the larger, 

 heavier particles are deposited at the bottom of the 

 basin. Generally, however, after this subsidence has 

 taken place, the finer, lighter particles and micro- 

 organisms remain in suspension in the water, as well as 

 substances in solution ; and the final purification can 

 only be effected by filtration, assisted often by aeration, 

 and sometimes by chemical processes. 



After an introductory chapter and a chapter on intakes, 

 sedimentation, and settling basins, the author proceeds to 

 the consideration of his main subject, filtration. Two 

 methods of filtration are described for the purification of 

 water-supplies, namely slow sand-filtration, denoted as 

 the English method, from its first introduction and general 

 use in this country, and rapid sand-filtration, requiring 

 the preliminary addition of a chemical solution, termed 

 a coagulant, to render this rapid system efficient, which, 

 being a distinctly American invention, is called the 

 America'n method. Two chapters are devoted to the 

 consideration of each of these methods in succession, the 

 first in each case discussing the theory, efficiency, and 

 influences of different arrangements and modifications of 

 slow, and of rapid sand-filtration respectively, and the 

 second chapter dealing with the design, construction, and 

 working of slow, and of rapid sand-filters. Following 

 these four principal chapters of the book, is a chapter 

 giving a summary of the relative merits of the two 

 methods of filtration ; instances in which a combination 

 of the two methods inight be advantageous ; and brief 

 descriptions of the Anderson, Pasteur-Chamberland, 

 Worms, and Maignen filtering processes. The book 

 concludes with a chapter on the location, design, and 

 construction of filtered-water reservoirs. 



The slow sand-filtration method for the purification of 

 water is well known, and its efficiency has been fully 

 established by long experience in England ; and it ap- 

 pears to be the only method, aided by aeration, by which 

 very turbid and polluted river waters, such, for instance, as 

 the waters of the tidal River Hugh, which have to furnish 

 the supplies for Calcutta and Howrah, can be sufficiently 

 purified to serve for a domestic supply. Rapid sand- 

 filtration is a comparatively novel method of purification ; 

 and the sand filters for this process consist usually of a 

 layer of coarse grains of quartz sand, 2^ to 3 feet thick, 

 placed in a tank of steel, iron, or wood, from the bottom 

 of which the filtered water is led, through strainers to 

 prevent the escape of the sand, into pipes for conveying 

 away the supply for distribution. Aluminium sulphate 

 has hitherto proved the most suitable coagulant, in which 

 the sulphuric acid enters into combination with the 

 calcium or magnesium carbonate in the water, setting 

 free the aluminium hydrate which forms flocculent masses 

 with the fine suspended matter in the water, and, adhering 

 to the grains of sand as the water passes through the 

 filter, covers them and the bed generally with a gelatinous 

 film, which arrests the bacteria as well as the finest 

 particles in the water, and ensures the efficiency of the 

 filter. When the filter becomes clogged by these im- 

 purities, as indicated by a reduction in the flow through 

 NO. 1 66 1, VOL. 64] 



it, the bed of sand has to be stirred up and pure water 

 forced up through it to remove the sediment. A rapid 

 flow is less liable to be interrupted by frost ; but the pro- 

 portion of coagulant required in a rapid filter changes 

 with the varying composition of the river water, and 

 necessitates the constant supervision of an experienced 

 chemist to regulate the dose to the conditions, for too 

 small a quantity would reduce the efficiency of the puri- 

 fication, and too large a dose would impregnate the 

 filtered water with alum, and, during the period of low 

 alkalinity in the flood stage of the river, would leave free 

 sulphuric acid in the water, which would be injurious to 

 the pipes. 



INTELLIGENCE AS THE SOUL OF THE 

 UNIVERSE. 

 Modem Natural Theology; With the Testimony oj 

 Christia?i Evidences. By Frederick James Gant, 

 F.R.C.S., &c. Pp. xii-H5i. (London : Elliot Stock, 

 1901.) Price IS. bd. net. 



IT is no doubt true that the older form of the " argu- 

 ment from design " is more or less discredited by 

 the doctrine of evolution. Nevertheless, the author of 

 the book before us is justified in holding that the argu- 

 ment itself is not disposed of, and that in a setting more 

 strictly accordant with our present knowledge than that 

 which Paley gave it, it is still a powerful weapon in the 

 hands of the natural theologian. More, indeed, is gained 

 under the conception of organic growth than is lost by 

 the sacrifice of the older teleology ; for Paley's statement 

 of the case savours of deism, whereas under the more 

 recent view there are distinct indications in, the universe 

 of a purpose which may be called moral. In so far, as 

 such a purpose is discoverable in nature, to that extent 

 does deism retire into the background. This is the 

 aspect of the matter which is put forcibly, if not very 

 intelligibly, in the work before us. The difficulties in- 

 herent in the materialistic as well as the deistic position 

 are, on the whole, well stated, and the way is shown to 

 be open for the recognition of intelligence as the " mind 

 or soul of the universe." Though the author guards 

 himself in words which are capable of an orthodox inter- 

 pretation, it may be questioned whether the argument 

 from nature, in his way of presenting it, necessarily ex- 

 cludes pantheism. Mr. Gant would probably appeal to 

 the second part of his book — which, dealing as it does 

 more particularly with historical evidences, is somewhat 

 outside our province — as supplying the needful correc- 

 tive. On the whole, however, it must be allowed that, 

 though his personal convictions are not in doubt, his 

 reading of natural phenomena is more successful as a 

 criticism of the deistic position than as an attack on 

 pantheistic interpretations. 



The book would have been better adapted for its pur- 

 pose if its author had developed his argument in simpler 

 language and with stricter attention to the ordinary rules 

 of composition. Instances of confused diction are 

 numerous ; for example : — 



" In all sentient living beings, mind is much moved 

 by suffering for the maintenance, and thence the pro- 

 longation of life" (p. 54). 



"Thus living beings tell their own story of identifica- 



