ture corresponding to a given proportion rect utilization of heat will correspond in of combustible gas, and consequently to this respect. We equally conclude from a known pressure after combustion, there this that, as far as possible, we must only is a certain length of suction we employ one gas cylinder in each separate should say "inlet in case of a steam machine. But dispersion depends also cylinder for which the work developed upon time. Cooling, then, will be as in the cylinder is a maximum. The va- much greater, other things being equal, riation in amount of suction answering as the working pace is slower. Now, a in each case to the maximum of work, more rapid working pace seems to imply being confined within narrow limits, the as a consequence cylinders of a smaller use of a slide will perfectly suffice to ob volume; but this contradiction disappears tain the greatest variation in the yield of when one reflects that the length of combustible gas. The arrangement, stroke is not necessarily related in an intherefore, of the gas cylinders in the variable manner to the cylinder volume case in question can be made in the sim- for a given expenditure. In like manner plest manner with a common slide-valve, as for the elastic force of steam, the utilmodifying, it is always understood, the ization of the elastic force of gases re. forward and backward movements of it, quires that the expansion should be the to meet this particular requirement. most prolonged possible. In the arrangeArrangement with previous comment above described there is a maximum pression. The arrangement before de- of expansion for each particular case. scribed appears certainly the simplest Thus the effect is necessarily limited. that could exist. It will perhaps be the The advantage, therefore, rests with an only one applicable to locomotives. Then arrangement which will permit of giving the increase of utilized power resulting back to the machine that which we may from it will certainly be clear gain and call the free play of the expansion, that without any doubt out of proportion to is to say, the power of expanding so far the cost of setting up. But the true con- as we may think it convenient within the ditions of the best employment of the limits only imposed by the nature of elastic force of gases, at least its most things. Finally, the utilization of the important conditions, are not there ob- elastic force of gases still depends on served, and simplicity is, perhaps, only one element which is entirely their own, acquired at the expense of utility. These but which is at bottom intimately conconditions, in fact, are four in number- nected with the utility of prolonged ex(1) the greatest possible cylinder space with the least possible exterior surface; (2) the greatest possible quickness of action; (3) the greatest possible expansion, and (4) the greatest possible pressure at the commencement of the expansion. The dispersive power of gases, so favorable to the use of boiler tubes, is evidently, on the contrary, an obstacle to the utilization of elastic force developed in the gaseous mass. Now, we have seen that in the case of boiler tubes the efficiency -that is to say, the heat transmitted was proportional to the diameter of the tubes. The loss would, therefore, be in inverse ratio to the diameter in the case of cylinders. But that is only applicable to cylinders of very small diameter, and the loss decreases in reality in a more rapid proportion than the diameter in creases. Therefore, an arrangement which, for a given consumption of gas, will give cylinders of the greatest diameter will be that with which the greatest di pansion. This element is compression, which should be the greatest possible for the greatest effect. It can be easily seen that we are dealing here with heated expansion obtained after cold compression, which is a way of prolonging the expansion in some sort inverse to that which consists in causing a vacuum, a way to which steam could not adapt itself, it being always understood that all compression causes inevitably an equivalent condensation in such a way that, even supposing steam to be combustible, instantaneous heating would be rendered impossible by reason of it. We can, therefore, theoretically get as indefinite a utilization of the elastic force of gases by compressing them indefinitely before heating, as we can get an indefinite utilization of the elastic force of steam by indefinitely prolonging expansion. But practically we soon attain an impassable limit. It is that at which the raising of temperature due to previous compression brings about spontaneous ignition. In fact, in will also be appreciably constant. It will their continuing compression we shall therefore be possible to determine the only recover from the expansion up to limit of compression at which ignition this same point the work furnished by would become inevitable, and to arrange compression, less the loss occasioned by the machine accordingly. We shall thus all useless action. There, then, is the constantly have the absolute maximum limit imposed by the nature of things, effect for each proportion of combustible and the final advantage in respect of util- material. We shall at the same time be ization will rest with an arrangement freed from the intervention of electricity, which will permit of its attainment. The for, the starting being effected by the acquestion being thus propounded, the sole tion of the steam, the gases need never be arrangement really practicable consists introduced until the speed shall have beevidently in forthwith employing but one come sufficient for ignition to be procylinder, so that it is the largest possible, duced with certainty. In all cases comand further in reducing the resisting pression will favor instantaneous ignition movements of the gases to their absolute by helping complete mixture, and in raisminimum. Then, and for the same side ing the temperature. In fine, and with of the cylinder, we are naturally led to an initial temperature corresponding to a execute the following operations, in a pressure of five to six atmospheres in the period of four consecutive strokes: (1) boiler, ignition will be spontaneously Suction during an entire stroke of the produced with a degree of compression piston; (2) compression during the fol- reaching to about a fourth of the original lowing stroke; (3) ignition at the dead volume-at least, if we neglect the effect point and expansion during the third of dispersion. Then the pressure after stroke; (4) forcing out of the burnt ignition would attain barely thirty atmosgases from the cylinder on the fourth and pheres, and as we are dealing here with last return stroke. The same operations the case in which combustion is effected being reproduced on the other side of without excess of air, the pressure would the cylinder in a similar number of strokes necessarily be lower in all other cases. of the piston, there results a particular It is, therefore, probable that in many sort of single-acting machine, we might cases we can really attain the absolute say of half-power, but which evidently limit of utilization. To sum up, while satisfies the condition of largest possible cylinder, and at the same time that condition, which is still more important, of previous compression. We see at the same time that the velocity of the piston is the greatest possible in relation to the diameter, since we do in a single stroke the work for which we should otherwise take two, and we evidently cannot do more. The temperature of the gas coming from the cupola is appreciably constant. That of the external air relatively varies only between narrow limits. Then the initial temperature of the mixture at the moment of the suction into the cylinder THE DIAMOND DRILL IN NEW SOUTH WALES.-The diamond drill is doing good work in discovering or proving coal in various parts of the colony, the most im portant recently discovered being a seam of good coal, some 12 feet thick, in the parish of Heathcote, 28 miles from Sydney on the Illawarra Railway. The drill manifestly lending itself, in the completest possible manner, to the utilization of elastic force developed in the gaseous mass by combustion under constant volume, the arrangement now in question is not less simple than the preceding oneat least, unless we consider as a complication the necessity, or rather the convenience, of employing in some cases distribution by clack valves. This distribution is generally the most advantageous, and there is nothing to prove that it is not generally applicable even to locomotives, and, above all, to the case in question. pierced this seam at 847 feet below the surface. Hitherto all attempts to find coal near Sydney have been unsuccessful. When the Illawarra Railway reaches Heathcote it will be possible to send coal from the mine to Sydney by rail at a very moderate cost, and vessels will be able to coal at Port Jackson. WATER SUPPLY. BY WILLIAM POLE, F. R. S., M. Inst. C. E. Mr. PRESIDENT AND GENTLEMEN,- -It was with considerable diffidence that I undertook to deliver this lecture on Water Supply. You all know that we have in our Institution some veterans who have acquired world-wide fame in this department of engineering; and it was not till I had been assured that there was no hope of getting any of them to undertake it that I would listen to the application. I am not, as they are, renowned for the construction of water-works; but it happens that, during almost the whole of a long professional life, I have been occupied, more or less, in the study and discussion of matters connected with water supply, and I suppose it is on this account that the Council have done me the honor to apply to me. And, in reality, my task is not a very difficult one; for, thanks to the great ability and long experience of the masters of the craft, the modes of effecting water supply have been pretty well settled. My chief duty is to give a very general view, without much detail, of the principles and practice that appear to have been established in this matter, and if I can succeed in doing this clearly, it is all I can desire. known formulæ and tables which, by long experience, have been found fairly suitable for ordinary purposes. But later researches have shown that in many points they require amendment when a greater approach to accuracy is desired. These researches were made some years ago, by two French engineers, MM. D'Arcy and Bazin; and the points they chiefly laid stress on were two: In the first place, it had been usually assumed that the retarding force of the friction was independent of the nature of the surface of the channel. This was found to be an error, different materials requiring different coefficients. And then, secondly, it was discovered that the relations between the velocities of the current at different parts of the section had not been correctly determined, and had values varying greatly under different circumstances. I am not going further into these matters; they can easily be referred to if required. And having said this, I will proceed to the more practical views of water supply. In the admirable Introductory Lecture we have heard explained the general phenomena by which the great element, The prospectus of these lectures gives water, is delivered on the earth for our the general title of "The Theory and use. We have now to enter on what is Practice of Hydromechanics." I have more strictly the province of the engineer little to say about theory here, as the in regard to water. We have to show problems affecting water-supply works how the stores of this invaluable subare chiefly the same as for mechanical and structural engineering generally. stance can be, and are, made available for the use and convenience of man. This is done in many ways. The engineer has to provide and distribute supplies of water for the food and the various necessities of congregated populations. He has to make available the ample natural stores of mechanical water-power. He has to direct and control the natural flow of surface waters, by operations of drainage and river regulation. He has to take advantage of the fluid mobility of water, by using it to form highways of minimum traction in inland navigation. He has, There are certain simple and well-moreover, to design floating vessels to In regard to the theory of hydrodynamics, I may refer you to an able article lately published in the "Encyclopædia Britannica," by a Member of our body, who has made this subject specially his own, Professor Unwin; and as you will shortly have the pleasure of hearing a lecture by this gentleman, he will prob ably give you some remarks on the point. I will only say a word as to the special problem of the flow of water along channels of various kinds. ravel upon water. And he has to pro vide for the safe and convenient communication of such vessels with the land, by harbors, docks, and piers. All these works in the aggregate, with their almost infinite expanse of detail, constitute the great branch of our profession called hydraulic engineering; and this will form the subject of the remaining lectures of the present course. tion of hydraulic science, and its application to works of hydraulic construction. The expression, "water supply," in its general sense, may have a wide interpretation. It may refer to supplies of many kinds, and for many different objects. But there is one kind of water supply which stands pre eminent and before all others, namely, the supply to the inhabitants of towns. It was this that was probably in the minds of your Council when they drew the title of this lecture, and I shall not err in directing attention specially to it. But before I enter on my humble share of the work, I should like to mention an interesting historical fact, which I think is not generally known, namely, that it is especially to hydraulics that civil engi- I need hardly enlarge on the value of neers are indebted for their origin and water. I suppose it is the most importexistence as a separate and independent ant natural substance known, and the profession. most indispensable for maintaining the The term "engineer" was originally present order of things in organic life. applied to military men. Building-works The old Greek sentiment, "Apio TOν μεν in civil life were constructed by the architect, who in all ages has been a well-recognized practitioner. vdop, was a natural prompting; some ancient philosophers supposed water to be the primordial element of which every living being was composed; and this is so far true, that water forms a very large part of the bodies of plants and animals, and constitutes, either simply or in combination, the greater portion of their food. The need of water for the life, health, comfort, and occupations of mankind, is patent to everybody; and hence the provisions for a due supply of it, of proper quality, in ample quantity, and in a convenient manner, become an absolute necessity of civilization. HISTORY. A century or two ago, however, a new and peculiar demand arose in this wise. The great rivers in the north of Italy had relapsed, by neglect, into a very bad state, giving rise to disastrous inunda tions. The nation became alarmed, and the most learned scientific men of the day were consulted as to what should be done. This gave rise to a series of valuable theoretical and practical studies, which are of great historical interest, as having formed the basis of hydraulic engineering. The knowledge spread rapidly throughout Europe, and gave a great impulse to hydraulic operations generally. In the earliest times people helped But there was now a want of competent themselves from the nearest brooks or men to execute them. The architects streams. But this hand-to-mouth process found these new studies foreign to their was only available in certain places; and own proper business; and so a new class as it was observed by unmistakable signs of practitioners sprang up for hydraulic that the superficial strata of the earth works; with which soon became associ- often contained water, the idea occurred ated other works of analogous character. to some ingenious person that this water Such a class required a new name, and might be got at by simply making a hole this was easily found. It was noticed in the ground, or, in other words, “sinkthat the kind of work undertaken by ing a well." Wells are mentioned as these new practitioners corresponded to sources of water supply in the oldest that allotted to the engineers of the mili- records we have, and the art of sinking tary service; and the new profession and working them had arrived, in early adopted the same title, prefixing, how- ages, at great perfection. ever, the epithet "civil," to indicate that they were civilians, and so to distinguish them from their military brethren. But still even wells could not be got everywhere, and as populations increased, some further extension of water supply Hence the origin of the present term, became necessary. The simplest plan of "civil engineer," an origin which, as I meeting this want was to carry the water have said, was due entirely to the cultiva-in suitable vessels from the stream or the well where it was found to the places where it was required. And, primitive as this plan appears, it has lasted into quite modern days. I recollect, when I lived as a boy in a large English town, seeing water carried about for sale, in cans with a yoke, as milk is often carried here; and even a few years ago, being in a fashion able watering-place for my health, I was advised by the local doctor not to use the town supply, but to drink the water of a neighboring spring, brought round in a barrel on wheels every day. But the more appropriate device soon presented itself of conveying water from distant sources by means of conduits, slightly inclined, so as to allow the liquid to flow along them by its own gravity. This was, indeed, only a direct artificial imitation of natural streams. It is very old, and is mentioned by Homer. It began in leading streams along the surface of the ground; but it ultimately developed into the supply of towns by the ancient aqueducts with which you are all acquainted, and which culminated in the magnificent water supply of the Eternal City. forced it along pipes laid through the streets, to the places where it was required; and it is clearly stated by the well-known antiquarian authority, Stowe, that "the Thames water was conveyed into men's houses by pipes of lead." When this convenient system was once established, it was easily seen that the more ancient conduit supplies might also be adapted to it, by bringing the water into a reservoir at a high level, the hydrostatic pressure from which would answer the same purpose as the pumping pressure in the former case. This was done in the New River supply, brought into London in 1613. Here, therefore, we have the two types of pumping and gravitation supplies on which all succeeding works have been modeled, with only improvements in detail. The original London street pipes were, if small, of lead, and, if large, of wood. About the middle of the eighteenth century cast-iron pipes were used, but their high price prevented their general adoption for a long time; it was not till about 1810 that this material may be said to These aqueduct-conduits usually ter- have come into common use, and it was minated in public fountains within the only after that date that the water suptown, from which the inhabitants could, ply of towns could take any great develwithout much trouble or inconvenience, opment. This development did follow, get the water carried to their dwellings. in the attainment of a higher pressure, Everybody who has been in Rome has admired the fountains there, and they are very common in continental cities generally. and generally a better and more ample supply, and the improvements have been continually progressing to the present day. Before considering the various modes of effecting the water supply in towns, it is necessary to say a few words on two alike on all modes of supply. These are the quality of the water, and the quantity of it which is likely to be required. a QUALITY OF WATER. The next great step in municipal water supply, namely, that of delivering the water into the houses of the inhabitants, is of comparatively late introduction. It points of a general nature which bear depended on a considerable degree of mechanical advancement; for to carry out such a system it was necessary to convey the water in pipes under pressure. There is no doubt that pipes of earthenware, of wood, and of lead, were used by The quality of water to be supplied to the Romans to some extent, but they town is a matter of great importance. were very imperfect, and nothing existed This is a subject properly belonging to in the shape of such fitting as would be chemistry, and the aid and advice of a necessary for house supplies. The first professional chemist must always be application of the house supply that I called in upon it. But still, any engican hear of was in London, brought neer concerned in a water scheme would about by the historically celebrated water-be at a manifest disadvantage, if he did works of Peter Morice, the Dutchman, not know enough of the matter himself, established at London Bridge, in 1582. to enable him at least to form a prelimHere water-wheels were erected which inary judgment on the sources of supply. pumped the water from the Thames, and Rain-water, as distilled in the clouds, |