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FILTRATION OF WATER FITZWILLIAM. 



fall into the cavity made by the crooked parts of 

 the others; just as the latch that is fastened to a 

 door, enters into the cavity of the catch fixed to 

 the door-post, and there hooking itself, fastens the 

 door; for it is in this manner that one thread of a 

 feather is fastened to the other. 



This admirable structure of the feather, which 

 it is easy to see with the microscope, succeeds per- 

 fectly for the use to which Nature has designed it; 

 which use was, not only that the laminae might be 

 united, but that when one thread or lamina has 

 been separated from another by some external 

 violence, it might be reclasped with sufficient facil- 

 ity and expedition 



In the ostrich, this apparatus of crotchets and 

 fibres, of hooks and teeth, is wanting: and the 

 consequence is, that the filaments hang loose and 

 separate from one another, forming only a kind of 

 down. This constitution of the feathers, however 

 it may fit them to adorn a lady's head-dress, may 

 be considered an imperfection in the bird ; as wings 

 composed of these feathers, although they may 

 greatly assist it in running, do not serve for flight. 



FILTRATION OF WATER, (a.) So little 

 has been written on the subject of filtration of a 

 practical nature, that the art of conducting the pro- 

 cess upon a large scale is yet to be acquired. Se- 

 veral trials have been made on superficies exceed- 

 ing one thousand square feet, to ascertain the most 

 approved principle, and the fitness of the various 

 materials proposed to be employed. All the modi- 

 fications of lateral and ascending filters have proved 

 disadvantageous; difficulties have been encountered 

 in preserving the various strata in their assigned 

 position, according to the sizes of their component 

 particles; and effectual cleansing could not be ac- 

 complished without the removal of the whole mass 

 of the filtering medium. All devices by currents, 

 reaction of water, and other means, have also proved 

 either inefficient, or inconvenient and expensive. 



The mode of filtration adopted at the Chelsea 

 works is by descent, and the medium consists of 

 fine and coarse river-sand, comminuted shells, and 

 pebbles, and of small and large gravel. These ma- 

 terials are laid in a reservoir, their surface being 

 disposed in ridges, which presents to the spectator 

 .an undulated appearance. The first experiments 

 by descent failed ; sufficient care had not been 

 taken in the selection and separation of the mate- ! 

 rial. Explosions of condensed air in the tunnels i 

 for collecting the filtered water deranged the strata 

 occasionally, and were obviated by air-drains. The 

 filtration was, in one instance, stopped by the addi- 

 tion of fresh sand, without having previously re- | 

 moved the old sand, which should be applied as the 

 upper stratum ; although, in this case, the surface I 

 had been thoroughly cleansed previously, a film or 

 puddle was formed on the original sand, and was 

 sufficiently supported by the particles of sand to \ 

 sustain five feet head of water, at first acting to [ 

 impede, and eventually to stop the filtration. The ! 

 process was greatly improved by the introduction ' 

 of the small shells, such as are usually found at 

 Shellness, the flat surfaces of which overlap, and 

 assist in the great desideratum of separating the 

 sand from the gravel, and thus tending to preserve 

 the free percolation in the lower strata, which is 

 essential for ensuring filtration sufficiently rapid for 

 waterwork purposes. 



The strata on the site of the filtering- works, 

 under the vegetable mould, consist of loam, sand, 

 and gravel, overlying the London clay to the depth 



of thirty feet. The sand and gravel contain power- 

 ful land-springs, and the masses of ferruginous con- 

 glomerate they pass through are so great, that the 

 water is of an objectionable quality ; therefore, in 

 constructing the basin to receive the filtering ma- 

 terials, it was necessary to exclude all the land- 

 water by clay and cement walling. 



An excavation into the sand and gravel, of suffi- 

 cient depth to admit of the water from the river 

 flowing on to the filtering bed, would have in- 

 volved too great an outlay; and this circumstance 

 led to the construction of the basin, lit a level 

 which rendered pumping the water from the river 

 unavoidable ; but the consequent subsidence of the 

 water, and the command of a constant flow to the 

 filtering-bed, are advantages which result from the 

 expedient of pumping; and the interest of the 

 money saved has more than compensated for the 

 annual expense. The filtering-bed covers an area of 

 one acre, and there is an elevated reservoir of nearly 

 the same size. The lower stratum of gravel con- 

 tains the tunnels for collecting the filtered water. 

 They are built with cement-blocks, and partially 

 open jointed, two spaces of an inch and a half on 

 the bed, and the heading-joint of each brick being 

 open. The fine gravel, pebbles and shells, and 

 the coarse and fine sand, are laid upon the large 

 gravel. 



The water is let on to the filtering bed at nine 

 places, and the ends of the pipes are fitted with 

 curved boards to diffuse the currents of water, and 

 prevent the surface of the sand from being dis- 

 turbed. The interstices in the fine sand being more 

 minute than the subjacent strata, it is found that 

 the impurities are arrested near the surface, and it 

 has not been necessary to remove more than one 

 inch depth of the sand at any one time of cleansing. 

 This work is effected by scraping the surface every 

 fortnight, and upon a careful examination it has 

 been discovered that the sediment penetrates to the 

 depth of from six to nine inches, according to the 

 state of the Thames water; the greatest penetra- 

 tion occurring during the prevalence of land floods 

 in the river. Notwithstanding this, however, it is 

 not necessary to remove more than the depth 

 stated, which contains the grosser impurities, the 

 remainder tending rather to improve filtration by 

 rendering the interstices between the particles of 

 sand still more minute. From these observations 

 it must not be inferred that the process is merely 

 a fine mode of straining, for something more is 

 evidently effected; an appearance resembling fer- 

 mentation being discernible when the water is in 

 contact with the sand. 



The quantity of water filtered is from three to 

 four hundred thousand cubic feet daily, according 

 to the demand. The undulated surface of the fil- 

 tering-bed admits of parts of it being worked, and 

 others drained ; and it aids in cleansing, by admit- 

 ting the grosser particles of the silt to slide down 

 the ridges, and form a sediment easily manageable. 

 The removal of the sand is effected by lifting por- 

 tions of the fine sand in succession, and placing 

 fresh sand of the same description underneath 

 them. 



FITZWILLIAM, EARL. The Right Hon. 

 William Wentworth Fitzwilliam, fourth earl Fitz- 

 william, of the county of Tyrone, was born May 

 30th, 1748, the elder son of John the second Earl, by 

 lady Anne Wentworth, eldest daughter of Thomas 

 first marquis of Rockingham. He was only in the 

 ninth year of his age at the death of his father, 



