Volltext Seite (XML)
1841.] THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. or strained when the valves are full open, a very small increase of the speed of the machine will cause the valves completely to cover the ends of the jet-pipes, and when the ends of these pipes are closed, the water can have no power to turn the machine. From this it will be clear, that the machine can be made so that, when it is doing very little work, it will not move at a much greater speed than it will when acting with its greatest power. The new water-mill acts on a principle similar to that of the well- known Barker's mill; but the arms are bent and otherwise shaped, so as to allow the water to run from the centre to the extremity of the arms when they are in motion, in a straight line, or nearly so, and in this way the disadvantages of carrying the water round with the arms, as is the case in Barker’s mill, are got rid of. The curve of the arms is such as to allow the water to run from their centres out of the jet-pipes, without being carried round by the machine, when it is in motion at its best speed. On this account, the rotary motion of the arms will not give to the water a centrifugal force. So the forces which work the new water-mill are simply the force of reaction, and the weight of a column of water of the same height as that acting on the mill, having the area of its cross section equal to the sum of the cross-sectional area of each jet-pipe. When the machine is standing, the one of these forces is as great as the other; but when it revolves so quick that the centres of the jet-pipes move at the same speed as that of the water flowing from them, the force of reaction ceases, as then the water falls from the jet-pipes without any motion, in a horizontal direction, for the machine leaves the water as fast as the acting column can follow it. When the re sistance to be overcome is as great as will balance the force caused by the weight of the water, there is still the force of reaction left to bring up the speed of the machine; and as the weight of the water remains the same, whether the machine is in motion or at rest, the force of reaction will carry up the speed till the centres of the jet-pipes re volve at u velocity the same as that of the water issuing from them before it ceases. Thus the machine, when its jet-pipes revolve at a speed as great as that of the water issuing from them, will give its maximum of effect, which maximum will be equal to the whole power of the water it uses ; for, in the time a given weight of water is ex pended, in the same time the machine is able to raise as great a weight from the level of the centres of the jet-pipes to the level of the surface of the water in the lead. There is of course a small part of the power lost, most of which is that caused by the resistance which the water meets with in passing through the main pipe and the machine. This portion of the force is very inconsiderable, as will be shown in the next paragraph: and, by making a slight alteration on some parts of the machine, this small fraction of loss may he still farther diminished. A machine erected lately for Messrs. Neill, Fleming, and Reid, at. their works, Shaws-water, Greenock, gives, when tested by the fric tion apparatus invented bv M. Prony, 5 per cent, of the whole power of the water which works it. The power of the water is 70 horses, and the power of the machine is equal to that of 59 , '25 horses or 75 per cent, as now stated. Mr. Stirrat’s water-mill of 2i horses’ power is the first that was made; it was tested in the same way as the above- mentioned machine, and the result of the experiment was equally favourable. The following are some of the advantages which the hydraulic ma chine of Messrs. Whitelaw and Stirrat, lias over an overshot water wheel of the best construction. The new mill has a governing appa ratus, which renders its motion as uniform as that of the best con structed steam-engine ; when a part, or even the whole, of the ma chinery which it works, is thrown of!' at once, the variation in the speed is scarcely perceptible. The speed of the new machine is well suited for every purpose: generally speaking, it can he formed to make the required number of turns in a given time, and on this ac count, intermediate gearing is done away with. There is little wear and tear on the pints of the new mill, for Us weight is perfectly balanced by that of the water, thus taking away almost all friction, and conse quently wear, at the rubbing parts: five of these machines are already in operation, and not a workman has been employed in any way at either of them since they were first set a-going, although one has been in constant use for nearly two years. The new machine takes up re markably little room. No very expensive building or other erection is needed for the fixing of the new water-mill, and the cost of the ma chine itself is very trifling in every case, and especially on a high fall, where an overshot wheel, as also the building and excavation required for it, become enormously expensive. On a fall of very great height, where to erect an ordinary water-wheel would be altogether out of the question, the new water-wheel may be employed to great advantage. The new machine may easily be made to rise or fall according as the water in the tail-race is high or low, and one form of it will work to very considerable advantage in tail-water. The best constructed over shot water-wheel will not, after the speed is brought up for ordinary purposes, give more than 70 per cent, of the whole power of the water which works it; and the new machine, as has already been shown, gives 75 per cent., and it can be formed to give even a greater portion of the power of the water than this. SUPPLY OF WATER TO THE METROPOLIS. It is always with much pleasure that we approach this question, in teresting as it is not only to the profession, but also to the public at large, being one of those subjects on which both parties meet as on common ground. The supply of water to the population has always with the supply of food generally acquired great political importance, and the. provision for it has called forth some of the greatest triumphs of engineering. It has been but too truly stated by Dr. Southwood Smith, in his able Reports on the Health of the Metropolis, that an in sufficient or impure supply of water is one of the main causes of dis ease in all classes of the community, and the means of removing which are well known to be in existence. The valuable report which we now lay before our readers, proves most clearly to every unbiassed mind that London may be supplied with pure water without having recourse either to the Thames, or to any other river. All rivers and open canals are infected in some de gree with vegetable and animal matter, partrcularly after heavy rains— for instance, even the New River is the receptacle of the land drain age for many miles. The water-works which derive their supply from the Thames are all within the range of the tide, impregnated as it is with the drainage of the metropolis, and the large manufac tories on its banks, and so must it always be. The works which stand the farthest up the river, those of the Grand Junction Company at the London end of Brentford, are within the immediate vicinity of large gas works, a soap manufactory, and the drainage of a brewery, and of one of the largest distilleries, without reckoning the drainage of the whole town. To the Provisional Committee of the London and Westminster Water-Works, Gentlemen - —The insufficiency and badness of the present supply of water to the metropolis have long engaged the public attention; hut although many endeavours have been made to establish it on a better basis, owing to causes which we must seek in the elements of the projects themselves, they have invariably failed. As it appears, however, generally admitted, that something should he done, we are naturally led to inquire into the reasons of the want of success of former attempts, and by carefully avoiding these, and at the same time en deavouring to present an effective and practical remedy, we may still hope to deserve the public confidence. It will, therefore, he my endeavour to show, in the following report, that Nature has supplied us with the means of sub stituting a pure and unceasing llow of spring water for the outpourings of filthy drains, and that this can be done without encountering difficulties of any but an ordinary nature. Nevertheless, before I proceed to do this, it may not be useless that I should briefly enumerate the various plans which have hitherto been sug gested to attain this object: as this will at once prove how much time and attention, not only numerous private individuals, but even the legislature, have bestowed on the subject; and will also enable me to point out to you what appear to me to have been the causes of their rejection. So far back as the year 1821, a committee of the House of Commons made a long report, in which they recommended that a bill should lie passed to regulate the water companies, which had at that time caused much dissatis faction, on account of the great increase, which a coalition enabled them to make, on their former rates. The inquiry, although it does not appear to have led to any positive result, nevertheless, called the attention of the pub lic to various facts which were not previously generally known, and among others, to the very inferior quality of water which many of the companies supplied. We accordingly find, that in 1821, a highly respectable body of gentlemen held a meeting, to take into consideration a proposition of Mr. Philip Taylor’s, to conduct the water of the Thames, by means of a subter raneous aqueduct, from a point near Richmond, to reservoirs at Kensa! Graen and Hampstead Heath. In 1825, a company was formed to supply the metropolis with spring water, from beneath the London clay, a project which was again brought for ward in 1835, and to which I shall hate occasion, in a later period of this Report, to allude at some length. But it was not until the sitring of 1827 that in consequence of the publica tion of a pamphlet, entitled “ The Dolphin,” by Mr. Wright, the general mass of the inhabitants of London could be said to have been aroused to a sense of the paramount importance of a better supply of water to their houses, than that derived from some of the most foul portions of the river Thames. Al-