WATER SUPPLY. 



WATER SUPPLY. 



curioiu MI iiniirht into their municipal life as the ' Commentaries' of 

 this anth r. It may be added that the total length of the eleven first- 

 naaied aqueducts was not leal than, 466,987 yards, of which 

 jardi were built upon arches. The highest point of ground in Uie city 

 waa the Mom Equiliuiis, which wan 144 (eet 8 inches above the level 

 of the invert of the Cloaca Maxima, but the aqueduct of the Anio 

 Novus discharged iu waters at the level of 156 feet 10 inches above 

 the same datum. The flow of the water* attributed to the public 

 aervice a constant, by night at well as by day ; and the private con- 

 sumer had the name i rivilege if he desired it. 



The Human emperors were far from confining their attention to the 

 water supply of Koine itself, for numerous and gigantic works of that 

 description, for the suppl- of iin|Kirtant provincial towns, were executed 

 by thrir orders. [AQUEDUCT.] Luring the decline of the lower empire, 

 even, the construction of aqueducts and of reservoirs was carried on with 

 the same degree of energy as in the brighter periods of the Roman rule ; 

 and the neighbourhood of Constantinople possesses ruins of the aqueduct 

 of Justinian, and in the valley of Bourgaa, which may rival any of the 

 earlier structures in magnitude at least, if not in constructive skill. 

 Perhaps the most remarkable parts of the water-works of Constanti- 

 nople were, however, the subterranean reservoirs there constructed to 

 store the water. One of them is about 819/200 cubic feet in capacity, 

 and the other about 1,028,970 cubic feet, and they are vaulted 

 throughout 



uf course the art of distributing water suffered under the effects of 

 the irruption of the barbarians ; and all that was done by even the 

 most enlightened of the rulers of the Gothic, Vandalic, and Lombardic 

 tribes was to repair and maintain the aqueducts they found to be in 

 existence when they overran the provinces of the Roman empire. 

 There is a tradition connecting the erection of the aqueduct of 8po- 

 leto with the name of Theoderic the Goth ; but the style of the 

 monument, and many other indications it furnishes, would throw 

 great doubts on the correctness of the story ; nor can we discover any 

 authentic records of the execution of any great works for the supply 

 of water to towns during the meducval jieriod. until about the end of 

 the 13th century. In fact, the great centres of population in modern 

 times were but* very insignificant villages in the early periods of his- 

 tory ; and property was held by far too uncertain a tenure to justify the 

 execution of great public works. The Italian cities seem to hare been 

 the first to attempt anything like a systematic distribution of water ; 

 ami .Michael Boceanegra, at Genoa, in 1278, the unknown authors of 

 oleto and of the Civita Custellana aqueducts, at other periods 

 in the Middle Ages, revived the modes of construction adopted by the 

 Romans. In the north of Europe there do not appear to have been 

 made any attempts to rival the gorgeous monuments of the Roman 

 empire ; and in nearly all cases as at London and at Paris the system 

 adopU-d seems principally to have been to lead to some stone re 

 the waters of springs rising in the country, by means of wooden or of 

 leaden pipes. Win n the populations of those towns had increased to 

 a considerable extent, it was found, however, that, as in the former 

 case of Home, it was no longer possible to obtain the necessary 

 quantity of water from the superficial gravels, or from the 

 bearing strata around them ; and we accordingly find that at the close 

 of the mediaeval period efforts were made to secure water-supplies to 

 the large towns from larger areas than had previously sufficed. In 

 France, the engineers seem to have considered themselves bound to 

 return to the traditions of {he Romans, and the aqueduct of Arceuil 

 was built in avowed imitation of the analogous structures of the 

 ancients In England, the system of contouring the hills by open 

 water-courses prevailed ; and the Plymouth Leet, established by Sir 

 F. Drake, and the New River by Sir H. Myddelton, may be cited as 

 illustrations of the system long adopted here. The great aqueduct of 

 Lisbon, erected between 1713 and 1732; the aqueduct of Caserta, 

 erected by Vanvitelli about 1763 ; the aqueduct of Sytneto. erected by 

 Prince Bwcari, in Sicily ; the Croton Aqueduct, and the Roqucfavour 

 Aqueduct, may be referred to as illustrations of the modem execution 

 of works for the supply of water, designed upon the principles of the 

 ancients ; but the majority of the modern water-supplies ore executed 

 hi a far less ostentatious manner, and with modifications required by 

 the local habits or by the municipal organisation of the towns them- 

 selvea. Of late years, also, the improvements which have been effected 

 in the machinery used for the purpose of raising water, and the new 

 applications of uieUlluigy to the building arts, have so pr. 

 changed the economical conditions of the distribution of . 

 is hardly possible to compare thu systems which have rcsp. , , . h |, : ,. 

 Tailed in ancient or in very modern times. The fundamental il. 

 eeuis, however, to conaUt in this, namely, that the state tin 

 the execution of the water supplies of antiquity, whilst in i 

 times they have been left entirely to nmniciilities or to 

 indutry. What the moderns may have gained in economy under 

 these circumstances, they have lost in art; and just precisely as the 

 economical element of the calculation prevails, so does the manner in 

 which a modem water supply is effected lose all character of beauty as 

 * monument 



Before entering upon the consideration of the technical questions 

 jcronected with the subject of a water supply, and before quitting the 

 port history oT those operation*, It may be desirable again to dwell 

 .ipon a very generally received opinion with respect to the assumed 



ignorance, by the ancients, of the principle of the inverted syphon ; or 

 of the principle by which water will tind tho same level at tha two 

 end* of a continuous pipe, unless prevented by some external force. 

 This opinion has been repeated in so many popular works upon 

 that it is aluuwt universally believed ; yet, not only does the aqueduct 

 of Patara entirely refute it, but the great syphon upon the coune of 

 the aqueduct of Lyon proves that the ancients were as well acquainted 

 with the principle as the modems themselves are. It is the more 

 cxtr.iordin.iry that this singular opinion should have obtained such 

 universal credence a* it has done, because Vitruvius discusses in a very 

 practical spirit the mode of executing the descending and a 

 pipes, in chap, vii lib. 8 ; and he point* out the precautions to be 

 taken to prevent the rupture of tho pipes by the compression of the 

 air in the lowest parts of the syphon. 



The first inquiry at the present day, when it may be desired to 

 execute a system of water supply to a town, after having ascertained 

 0fhe present and the probable future extent of the coiiMimptiou (which 

 is usually reckoned to take place at the rate of forty gallons per head 

 of the population per day), must of course be, as to where a permanent 

 supply of water of a proper quality is to be obtained. Much discussion 

 bos of late years taken place with respect to the question as to u i< ,l 

 constitutes the proper quality of such a water, and the formerly 

 received opinions of physiologists and engineers have been boldly 

 challenged by men who have had little chum to either of those titles. 

 The discussion has principally turned on the subject of the hardness 

 and of the softness of waters, consequent upon the presence in them 

 I of the salts of lime, in the form of the bicarbonatea of that base ; the 

 | former authorities upon such matters contending that a certain pro- 

 portion of lime is necessary in a potable water, whilst the new lights 

 contend that absolute purity should be aimed at. The truth, in this 

 case, seems to be that there is still too considerable an amount of 

 uncertainty with respect to the real action of the salts in q: 

 upon the human frame to allow of the formation of any very 

 opinion on the subject, or of the entaUi )un> nt of any absolute law for 

 the adoption, or rejection, of a particular source of rupply, 

 departure from the standard of absolute purity is very small. Local 

 considerations of economy must, iu the present stato of knowledge, 

 exercise great influence upon the choice of the source of supply ; and 

 it is only when the quantities, or some peculiar properties, of the extra- 

 neous impurities, are very objectionable, that it becomes desirable to 

 reject a source which is close at hand. The qualities which are indis- 

 pensable in a v, atvr designed to be- distributed in a town, are, to 

 the words of the ' Annuaire des Kaux de France.' that " it should be 

 fresh, limpid, and without smell ; that its flavour should be hardly 

 perceptible, and that it be neither disagreeable, Hat, brackish, nor 

 sweet ; that it should contain little foreign matter, but a authVii nt 

 quantity of air in dissolution; that it should dissolve soap without 

 leaving curds, and should cook vegetables easily." A small in : 

 carbonic acid gas increases the wholesomeness of a water, by its 

 influence upon the digestive organs ; but it enables the water to take 

 up an additional quantity of the salts of lime (which in their turn 

 increase the hardness of the water), and to develope some forms of 

 disease (such as gout, calculi, &c.) in the populations using it habitually. 

 Waters containing salts of magnesia, or of sulphate of liuie, are con- 

 sidered, on the other hand, to produce the loathsome disease the ^ 

 and the very purest waters obtained from the melting of iee, or of 

 snow, are deficient in some elements necessary to maintain the healthi- 

 ness of the human frame. The waters which hold in solution notable 

 proportions of organic matters, are, however, those which ore the most 

 objectionable; and diarrhoea, dysenteries, and other acute and ch ionic 



diseases may be traced to the use of tho water obtained (mm u. 



marshes, or wells, containing excessive proportions of alien d . 

 matters, either in suspension, or in solution. It wan considered, by > he 

 authors of the 'Annuaire des Eaux,' that the small quantity oi the 

 chloride of sodium to be found in ordinary river or spring wat. 

 rather advantageous than otherwise; and they further remark, that the 

 chlorides in water ore almost always associated with the iodides and 

 bromides, which unquestionably increase its salubrity. It n 

 added, that when the proportion of the bicarbonate, of liine in a ] 

 water exceeds 1 in '2UUU, it becomes positively injurious ; that thu 

 bicarbonate of lime is thrown down by boiling; but that neither the 

 salti of magnesia, nor the sulphate of lime, are thus expelled. 



The opinion \\lii li it hii.i lately been attempted to convert into a 

 law, " that the nearer the source, the purer the supply," seems to be 

 one of those half-truths which require to be acei-pted with a h 



Tim , the waters rising from deep-seated springs in the chalk 



utain at their source an abnormal dose of the 



of lime, which they part with if allowed to flow in the open air iu a 

 :i:umel. Indeed, so much do waters generally improve by the 

 flow in open channels, that some of the ablest physiologists hold that 

 river waters alone should be used for town supplies ; but in such cases, 

 it is essential to adopt precautions with a view to the prevention of 

 tho contamination of the latter, by the organic impurities \\.u-hed 

 down from the lands they traverse. A prolonged course over a 

 channel also removes earthy impurities, and the hydrous oxides, 

 which are often held in suspension in spring waters ; but it does not 

 seem to have any influence upon the sulphates of lime, or < 

 or upon the chlorides of calcium or of sodium. la all cases v. ! 



