WATER. 



from Cotnifton and Swanfton, in leaden and iron pipes ; 

 but the fupply is very inadequate to the fize of the 

 city. 



When water is to be conveyed in an open canal, like the 

 New River, the manner of fetting out and executing the 

 work is fo nearly the fame as for a navigable canal, that it 

 is unn'ecefTary to fay more than we have already given in 

 our article Canal, except the rules for calculating the ne 



courfe, which is a channel of ftone, and on each fide of it is 

 a narrow path wJth a parapet, which renders it fafe to walk 

 along the fide of the aqueduft when it requires cleaning or 

 repairing. 



In the Philofophical Tranfaftions, it is ftated that this 

 aqueduft is 2560 fathoms in length, and confifts of 242 

 arches ; the fpan of each is 65 fathoms, and the thicknefs 

 of each pillar to futlain the arches 4 fathoms. On the fide 



ceflary flope or defcent to produce the required velocity of of the valley next to Maintenon, there are thirty-three fingle ' 



the water ; and the beft theorem for this purpofe we have 

 already given in the preceding part of the prefent article. 



We (hall only add a few particulars of fome of the largeft 

 modern aquedufts for conveying water. 



Aqucduas. — BeUdor ftates, in his Architefture Hydrauli- 

 que, that one of the fineft fubterraneous aquedufts in France 

 is that of Arcueil, which condufts the water from many 

 coUcfting channels in a ftone channel. It is fituated in the 

 countries of Rungis, Paret, and Coutin. This aqueduft is 

 14,920 yards in length, and is conftrufted in free-ftone ; it 

 extends from the valley d'Arcueil to an elevated water-ciftern, 

 or chateau d'eau, which is at the Porte St. Jaques. The chan- 

 nel has an inchnation of 6 inches in 400 yards, or i in 2400. 



On each fide of the water-courfe is a raifed foot-path 

 19 inches wide, upon which a pcrfon can walk as far as the 

 village d'Arcueil. The height of the paffage from the bot- 

 tom of the water-trough to the under fide of the arch is 6^ 

 feet, except in fome places where they have been obliged 

 to make them lefs, in confequence of the high roads beneath 

 which it pafTes. 



Another fubterraneous aqueduft of this kind is that of 

 Rocquancourt, which conveys water to Verfailles ; it is 

 3623 yards in length, and in all the length has an inclination 

 of only 31 feet, which was the utmolt that could be given 

 it. To conftrudl this aqueduft, they were obhged in many 

 places to dig to a depth of 30 yards, which rendered the 

 execution of it very difficult. One hundred and fifty (hafts 

 were made in the length of this aqueduft. They were not 

 made at equal diftances, but only in fuch places as would 

 facilitate the conveyance of materials ; eighty of them were 

 lined with ftone, and the other feventy, which were not 

 required to laft longer than during the conftriiftion, were 

 only lined with wood, and ftopped up afterwards with a 

 dome of mafonry, and filled up with earth to the level of the 

 furface. 



This aqueduft coft 325,000 livres. From 1675 to '^7^ 

 it never yielded more than 6 pouces of water, and fome 

 times gave only 5, 4, 3, or even 2 pouces, according as the 

 dry feafons were of greater or lefs duration. The pouce de 

 fontainier is a meafure of running water ufed by French en- 

 gineers, which amounts to about .48 Engli(h cubic feet 

 ptr minute ; hence the 6 pouces would be 2.88 cubic feet 

 per minute. 



A pond was made in 1685 at the head of this aqueduft, 

 to drain a country called Trou d'Enfer ; and fince then it 

 has given lo and 12 pouces, i. e. 4.8 and 5.76 cubic ieiX. per 

 minute. 



When water is condufted in an open channel, it fre- 

 quently becomes necelTary to crofs deep valleys ; in this cafe, 

 the channel mud be fupported on arches like a bridge. This 

 was the objeft of thofe vaft Roman aquedufts, of which we 

 find the remains at Nimes, Aries, Frejus, &c. The great- 

 eft modern ivorksof this kind are thofe conftrufted in the time 

 of Louis XIV. to conduft water to Verfailles and Marly. 

 One of thcfe is the aqueduft of Maintenon, for conveying 

 the river Bnre to Verfailles : it confifts of three courfes of 

 arches, raifed one above the other, to fupport the water- 



arches, afterwards feventy-one double ones, ( that is, having 

 one arch upon another,) then forty-fix treble ones ; at this 

 part the water-courfe is generally 216 feet 6 inches high from 

 the ground up to the floor of the water channel ; afterwards 

 there are feventy-two double arches, then twenty fingle ones, 

 which laft reach to a mound of earth, which is raifed 50 feet 

 high above the ground for a great diftance. 



The general height from the ground up to the fecond ar- 

 cade or row of arches is 16 fathoms ; from the fecond row 

 to the third or upper arcade 14 fathoms ; in the upper ar- 

 cade, the arches are double the number of thofe they ftand 

 upon ; above this is 6 fathoms 6 inches more to the door of 

 the channel, which is at leaft 7 feet high befides the pa- 

 rapet. 



The pillars at the ground are 8 fathoms thick, but with 

 the Hopes and (hortenings, which are made in every ftory ; 

 the top where the channel runs is reduced to 20 feet broad. 

 There is likewife at each pillar a buttrefs projefting one 

 fathom, and two fathoms wide to ftrengthen the pillars. 



There is another great aqueduft raifed on arches in the 

 Plaine de Bue, which condufts water to Verfailles from the 

 Plaine de Scale. This is built with two ranks of arches, 

 and the lower ones are fo much wider than the upper, as to 

 aflford room for a carriage-way acrofs the valley about half 

 as high up as the water-courfe. Drawings of thefe great 

 works are given by Belidor. 



It ij difficult to determine the exaft (lope which (hould 

 be given to a water-courfe, in order to conduft a given quan- 

 tity of water; it can only be known by calculation accord- 

 ing to the rules we have already given, and which are founded 

 upon experience. Vitruvius recommended a flope of i foot 

 fall in 200 feet in length ; but Behdor fays this is much more 

 than is necelTary, and that i foot fall in 3600 feet of length is 

 quite fufficient, when the channel is ftraight without elbows, 

 or fudden angles, or if the bends at fuch angles are by eafy 

 curves, fo that the water is not retarded in changing its di- 

 reftion. He remarks, that the canal from the pool of 

 Trappes, made by M. Picard to conduft the water to Ver- 

 failles, had 9 inches flope in 1000 fathoms, or l foot fall in 

 7998 feet long. When the water was run into this, it took 

 four hours to run 8526 yards, though it was urged by a pref- 

 fure of 38.3 inches. Alfo that the aqueduft of Rocquan- 

 court before mentioned has only 3 pieds fall in all its length, 

 which is 1700 toifes, that is, i foot fall in 3400 feet of length. 

 Whence Btlidor direfts as a general rule t0 make the fall 

 I inch in 100 yards, that is, l foot in 3600 feet, provided the 

 bottom of the trough is of fmooth (tone, and not muddy. 

 This is the leall which can be allowed, and more may be 

 given when the relative levels between the two places will 

 admit of a more rapid defcent. 



On the Conveyance of Water in Pipes — This is an objeft of 

 great importance. The ancients condufted water in pipes 

 only down hill ; but never carried it up again, not knowing 

 that water would rife to its own level ; but we can conduft 

 water to very great diftances, and bring it from one moun- 

 tain to another in pipes, which defcend into the intermediate 

 valleys and rife again, provided that the fpring or place from 



which 



