WATER. 



nuance ; but we do not think the latter a great objeftion, 

 for the water is not more liable to freeze there than in the 

 buckets or on the fhuttle, and may be prevented by the 

 fame means, wz. by keeping the wheel always in motion ; a 

 very fmall dream of water left running all night will be fufii- 

 cient. Mr. Smeaton always ufed fuch fweeps, and with 

 very good eflfeft; it is certainly preferable to any intricate 

 work in the form of the buckets. 



On Jetting out IVater-courfes and Dams. — The moft ancient 

 mills were underlhot-wheels placed in the current of an open 

 river, the building containing the mill being fet upon piles 

 in the river. It would foon be obferved that the power of 

 the mill would be greatly increafed, if all the water of the 

 river was concentrated to the wheel, by making an obftruc- 

 tion acrofs the river which penned up the water to a re- 

 quired height ; and alfo to form a pool or refervoir of water. 

 A fluice or (huttle would then become neceffary to regulate 

 the admiffion of water to the wheel, and other fluices would 

 be neceffary to allow the water to efcape in times of floods ; 

 for though in ordinary times the water would run over the 

 top of the obftruftion or dam, yet a very great body of 

 water running over might carry away the whole work, by 

 waffling away the earth at the foot of the dam, and then 

 overturning it into the excavation. This is an accident 

 which frequently happens to mills fo fituated, and the danger 

 is fo obvious, that moll water-mills are now removed to the 

 fide of the river, and a channel is dug from the river to the 

 mill to fupply it vrith water, and another to return the water 

 from the mill to the river. The difference of level between 

 thefe two channels is the fall of water to work the mill, and 

 this is kept up by means of a weir or dam entirely acrofs 

 the river ; but the water can run freely over this dam in 

 cafe of floods, without at all affefting the mill, becaufe the 

 entrance to the channel of fupply is regulated by ffuices and 

 fide walls. 



The dam fhould be erefted acrofs the river at a broad part, 

 where it will pen up the water fo as to form a large pond or 

 refervoir, which is called the mill-pond or dam-head. This 

 refervoir is ufeful to gather the water which comes down the 

 river in the night, and referve it for the next day's con- 

 fumption ; or for fuch mills as do not work inceffantly, but 

 which require more water, when they do work, than the 

 ordinary llream of the river can fupply in the fame time. 

 The larger the furface of the pond is, the more efficient it 

 will be ; but depth will not compenfate for the want of fur- 

 face, becaufe as the furface finks, when the water is drawn 

 off", the fall or defcent of the water, and confequently the 

 power of the water, diminifnes. 



The dam for a large river ftiould be conftrufted with 

 the utmoft foUdity ; wood framing is very commonly ufed, 

 but mafonry is preferable. Great care muft be taken, 

 by driving pile planking under the dam, to intercept all 

 leakage of the water beneath the ground under the dam, 

 as that loofens the earth, and deftroys the foundation 

 imperceptibly ; when a violent flood may overthrow the 

 whole. It is a common praftice to place the dam obliquely 

 acrofs the river, with a view of obtaining a greater length 

 of wall for the water to run over, and confequently prevent 

 its rifing to fo great a height, in order to give vent to the water 

 of a flood. But this is very objeftionable, becaufe the cur- 

 rent of water conftantly running over the dam, always afts 

 upon the fliore or bank of the river at one point, and will in 

 time wear it away, if not prevented by expenfive works. 

 This difficulty is obviated, by making the dam in two lengths 

 which meet in an angle >, tlie vertex pointing up the 

 ftream. In this way the currents of water, coming from 

 the two oppofite parts of the dam, ftrike together, and 



fpend their force upon each other, without injuriiig any 

 part. A flill better form is a fegment of a circle, which 

 has the additional advantage of ftrength, becaufe if the abut- 

 ments at the banks of the river are firm, the whole dam be- 

 comes hke the arch of a bridge laid down horizontally. 

 This was the form generally ufed by Mr. Smeaton. 



The foot of the dam where the water runs down ffiould 

 be a regular flope, with a curve, fo as to lead the water 

 down regularly ; and this part fliould be evenly paved with 

 ftone, or planked, to prevent the water from tearing it up, 

 when it moves with a great velocity. 



When the fall is confiderable, it may be divided into more 

 than one dam ; and if the lower dam is made to pen the 

 water upon the foot of the higher dam, then the water run- 

 ning over the higher dam will ftrike into the water, and lofe 

 its force. There is nothing can fo foon exhauit the force of 

 rapid currents of water as to fall into other water, becaufe 

 its mechanical force is expended in changing the figure of 

 the water (fee circular "jjeir in our article Canal) ; but when 

 it falls upon ftone or wood, its fc>rce is not taken away, but 

 only reflefted to fome other part of the channel, and may be 

 made to aft upon fuch a great extent of furface as to do no 

 vei-y ftriking injury at any one time, but by degrees it wears 

 away the banks, and requires conftant repairs : for it is de- 

 monftrable that, as much of the force of the water as is not 

 carried away by the rapid motion with which it flows, after 

 pafling the dam, muft be expended either in changing the 

 figure of the water, or in waffling away the banks, or in 

 the friftion of the water running over the bottom. 



The cotton-works of Meflrs. Strutt at Belper, in Derby- 

 ffiire, are on a large fcale, and the moft complete we have 

 ever fcen, in their dams and water-works. The mills are 

 turned by the water of the river Derwent, which is very 

 fubjeft to floods. The great weir is a femicircle, built of 

 very fubftantial mafonry, and provided with a pool of water 

 below it, into which the water falls. On one fide of the 

 weir are three fluices, each 20 feet wide, which are drawn 

 up in floods, and allow the water to pafs fideways into the 

 fame pool; and on the oppofite fide is another fuch fluice, 

 12 feet wide. The water is retained in the lower pool by 

 fome obftruftion which it experiences in running beneath 

 the arches of a bridge ; but the principal fall of the water is 

 broken by falling into the water of the pool, beneath the 

 great femicircular weir. 



The water which is drawn off from the mill-dam above 

 the weir pafles through three fluices, 20 feet wide each, 

 and is then diilributed by different channels to the mills, 

 which are fituated at the fide of the river, and quite fecure 

 from all floods. There are fix large water-wheels; one of 

 them, which is 40 feet in breadth, we have mentioned, from 

 the ingeriuity of its conftruftion ; and another which is 

 made in two breadths, of ij feet each, we have alfo de- 

 fcribed. They are all breaft-wheels. The iron-works of 

 Meffrs. Walker at Rotherham, in Yorkfhire, are very good 

 fpecimens of water-works ; as alfo the Carron works in 

 Scotland. 



The largeft works for overffiot-mills are in Rufiia, at 

 Colpino, near St. Peterfburgh, on the river Neva. They 

 were erefted principally under the direftion of Mr. Gaf- 

 coigne of the Carron works in Scotland, and have been 

 greatly improved by the prefent direftor, who is nn engineer 

 of his fchool. An immenfe dam of granite is built acrofs 

 the river to pen up the water, until it makes a lai'ge refer- 

 voir. The wafte and flood waters do not run over this 

 dam, but are condufted out of the refervoir by a femi- 

 circular branch of the river, and run over a great weir to 

 join the original courfe of the river below the works. The 



mills 



