ON THE SUPPLY OF LONDON WITH WATER, BY ARTESIAN WELLS. Rome, in the plenitude of its power and magnificence, was supplied with water by twenty aqueducts, through the medium of upwards of 1,300 reservoirs, which at the present day excite the utmost astonishment and admiration of every reflecting mind. Some idea may be formed of those stupendous undertakings, even by the general reader, from the following descriptions of three of them, the Aqua Martia, the (new) Anio, and the Aqua Claudia, to which nothing even approaching a parallel has been accomplished in modern times, saving our railways. The Aqua Martia began at a spring thirty-three miles from Rome, and, after a circuitous course of three miles, it entered a tunnel sixteen feet in diameter, whence it continued for thirty-eight miles, having also in its course a series of nearly 7,000 arcades, with an elevation of seventy feet. In various parts of this extensive aqueduct deep cisterns were formed, for the purpose of receiving the sediment deposited by the water; and at certain distances the upper parts had apertures for the escape of air that might be collected in the conduit. The water supplied from this source is represented to have been remarkable for its green colour; and Pliny, in his Natural History, particularly celebrates its excellence; for when treating of the qualities of waters, he thus eulogizes it: "Among the blessings conferred upon the city by the bounty of the gods, is the water of the Martia, the clearest of all the waters in the world, and distinguished for coolness and salubrity." "It is likewise remarkable that the Aqua Julia and Aqua Tepula conveyed their waters by the same course as the Aqua Martia, their respective channels resting upon arcades erected one above another: the latter was lowest, the Aqua Tepula formed the second, and the Aqua Julia the highest." The (new) Anio was constructed on a higher level than the old, with its course along the surface of the earth for 7,543 paces, when it entered a subterranean tunnel of the length of 54,267 paces. This structure was formed during the reign of Nero, and it contained more than 600 arches, some of which exceeded 100 feet in height. The Aqua Claudia, another of these stupendous works, was begun during the reign of Caius Cæsar Caligula, and completed during the reign of his successor, Claudius. This extraordinary edifice was built with hewn stone. It commenced at the distance of about thirtyeight miles from Rome, and its elevation was so great as to adapt it for supplying all the hills of the city, even the highest. It had a subterraneous course for thirtysix miles and a quarter; afterwards running along the surface of the ground ten miles and three quarters in length, it passed through a vaulted tunnel three miles, besides being continued for the extent of seven miles on arcades, some of them very lofty. This grand and extensive aqueduct still continues to afford its advantages to the modern city, and, from the great excellence of the water afforded by this source, has obtained the appellation of Aqua Felice.* Neither labour nor expense, in short, was spared by the ancient Romans to obtain water in a state of purity and abundance, to promote the salubrity of the city and the comfort and health of the inhabitants. On this subject Professor Leslie observes, "Trajan showed particular solicitude in improving the aqueducts. Those works were executed in the boldest manner; nothing could resist the skill and enterprise of the Romans; they drained whole lakes, drove mines through mountains, and raised up the level of valleys by accumulated arcades. The water was kept cool by covering it with vaults, which were often so spacious that, according to Procopius, who wrote in the time of Belisarius, a man on horseback could ride through them. So abundant, indeed, was the supply, as to induce Strabo to say that whole rivers flowed through the streets of Rome." The probable supply to the 1,000,000 of inhabitants of which Rome could one time boast, amounted to 50,000,000 cubic feet, being equal to about fifty cubic feet for each individual. This is probably twenty times the quantity which London now receives for each of its inhabitantsa fact which goes far to justify the application of the disgraceful term "bathless" to Matthew's Hydraulics. this, the largest, the most opulent, and the most powerful city in the world. How miserably insignificant do our water-works appear, and how trifling our supply they furnish to this mighty city of more than two millions, when contrasted with the immense flood of pure water poured into old Rome by her gigantic aqueducts! And how discreditable the difference between the two capitals, when we reflect on the far superior resources which modern science has placed at our command, and on the well-known fact, that, through the happy constitution of the strata on which London stands, she has at her command-requiring as it were but the smiting of the rock to make them gush forth-boundless supplies of the purest possible water! Attached to a house I occupied at Clapham more than thirty years ago, there was a well newly constructed of 300 feet deep, in which the water rose to within six feet of the top; and there was a well of similar depth on the other side of a narrow intervening valley, on a somewhat lower level, which sent forth a small perpetual stream. These facts attracted my notice, and led to my devoting a great deal of attention to the subject for several of the following years-indeed, I may say, ever since. Satisfied with the practicability of supplying the metropolis with pure water by means of wells properly disposed through the various districts, I attempted upwards of twenty years ago to get the principle adopted, but found the public mind not sufficiently ripe at that period to entertain seriously the proposition, and thus the affair dropped. London stands upon what has been termed a basin of clay, many miles in extent, and from two to three hundred feet in thickness; this clayey mass is underlaid by porous strata consisting of green sand, gravel, and chalk-the last named of immense thickness, never yet, I believe, entirely perforated. These underlaying strata crop out to the north and south of the clay, increasing in elevation more or less irregularly as they recede from and respectively rise to the surface, and form the subsoil of the country for hundreds of square miles in extent. These are saturated with water to their utmost depth, and consequently in proportion as the water therein becomes elevated above the lip of the basin, streams are formed which run over the surface and empty themselves into the Thames; hence the Brent, the Wandle, the Lea, &c. Now, if by means of wells through the clay to a depth of 400 feet the water were extracted from the underlaying strata, a course would be created to which the percolating fluid would naturally flow in abundance. In fact, it would be simply a mode of draining many thousand acres of the country, through the medium of the porous interstices and fissures beneath, instead of allowing it to make its way to the Thames above the surface. Hence, there is little probability of a deficiency in the supply, or the supply being in the least affected by the seasons, so long as the rivers above named continue to flow. The peculiar formation of the strata affords the means of effecting the object in the most perfect manner, as the clay can be penetrated, and wells sunk of suitable dimensions without obstruction from water, to a depth of nearly 200 feet before it is necessary to commence boring. Thus we are enabled to fix pumps for raising the supply so much beneath the natural level, until they can, by reducing the water in the well, create a head of sufficient pressure externally to force in a volume equal to the demand of the pumps, or till the demand and supply are reduced to an equilibrium, which would be difficult to accomplish in a soil differently constituted. 6 July, 1846. ALPHA. Limehouse. IS HEAT PONDERABLE?-TURKISH CEMENT. Sir,-In reference to Mr. Lloyd's communication in your last Number, I may state that, instead of "the opposite opinion," I should have said this opinion, as Young, Davy, and Rumford supported the opinion of heat being immaterial, or a quality of matter. Leaving this inadvertence or typographical error, I must confess that Mr. Lloyd's experiment and view is ingenious; but I should like to see some experiments made on other forms of matter, which allowed the use of the balance after the application of heat, before I said anything decisive on the subject: experiments, for instance, on the congelation of different fluids, and the comparative weights of equal quantities of such in a fluid or solid state. Water, we know, expands just before freezing; but the why, we seem at present to know not. It contracts to a certain point, and then suddenly expands, though heat still continues to be taken away from it. But leaving this point in statu quo, it must be confessed that the solid (ice) in the case of water, too, is lighter than the fluid (water,) and floats upon it, as Mr. Lloyd says cold iron does on melted. The water, too, has also more heat in it than the ice. Thus the grand point is in favour of Mr. Lloyd's view; and this, I trust, will be encouragement for him to pursue the subject further. I also shall reconsider this matter. I shall close this communication by stating that I have lately made some "lukium," exactly according to the recipe given by Mr. White, in his Three Years at Constantinople, (which recipe, I think, was copied into your journal,) and found the oil and lime (my lime was fresh burnt, as he recommends) separate after a few days. I think it probable, therefore, the Turks did not tell Mr. White some other particulars essential to making it successful. Your obedient servant, - Sir, The experiment of Mr. G. Lloyd, as detailed in your last, No. 1195, is by far too late of coming into the field to prove that heat is a ponderable body; other reasons must be sought to account for the phenomenon therein mentioned. It will, however, be readily granted that the deduction is a very natural one, if we were only assured that the premises upon which the conclusion is based were right, namely, that the iron in a fluid state is greater in bulk than when solid. I certainly do not maintain that it is not so, but it requires to be proved. It is well known that iron and other metals when heated occupy more space than when cold; there must however be some definite point or degree of temperature where this increase in bulk stops-and may it not be a law of nature that metals when brought to 35 the fluid state by heat shall begin to decrease rather than increase in bulk, with the increase of temperature? This would be by no means a greater anomaly in the laws of nature than that water increases in bulk during the procees of coolingthat is, when parting with heat from 40° to 32° F., which is just at the time it is beginning to assume the solid form-between which and the floating metal there is at least some similarity. Seeing that there have been so many experiments of the most delicate nature performed with a view to ascertain the ponderability or imponderability of heat, such as with fine steel yards and balances capable of being affected by the part of a grain, all of which have failed to detect the least augmentation in the weight of a body by the mere raising of its temperature, it would be hasty to conclude that because the solid portions of metal float upon the surface of that which is fluid, that therefore heat is ponderable. All the other metals, as well as iron, obey the same law, from which fact other, and perhaps as important deductions as that referred to, namely, that heat is ponderable, have been attempted to be drawn, but the true explanation of this phenomenon, like some other known properties of heat, or heated bodies, remains still a mystery-no doubt some day to be developed. Perhaps the next most important known, and yet unexplained phenomenon relating to heat is, that when certain, if not all, fluids are subjected to a much greater degree of heat than is absolutely necessary for their being converted into vapour, they will, under these very circumstances, take nearly fifty times as much time in being so, than with a much less degree of heat, although heat is the cause of evaporation. I believe that so far as we are acquainted with this fact at the present time, we are chiefly indebted to the investigations of M. Boutigny, who has clearly shown that when water is thrown upon a red hot plate it is instantly raised to a temperature of 205° F., which is 7° below the boiling point, and this temperature of 205° is invariably the same when the plate is sufficiently heated. One condition, however, is necessary to the water remaining at this temperature, namely, that it be allowed to remain in that form which it naturally assumes, which is nearly that of a sphere; the moment that form is disturbed the whole will be almost instantly dissipated in vapour. When the water, or other fluids, do assume this form which requires the plate to be considerably heated above that which would vapourize the fluid, it will then, under these circumstances, as above mentioned, be about fifty times as long in being converted into vapour, as when under the apparently less favourable circumstances of being thrown upon a less heated plate. Although no satisfactory expla nation can be said to have yet been given of this important discovery, still, in a practical point of view, it would be of the greatest benefit, as bearing upon the generation of steam and the prevention of boiler explosions. 1, Derwent-place, Bermondsey. S. EQUATIONS. ADDITIONAL REMARKS ON THE SUBJECT OF A LATE COMMUNICATION OF THE AUTHOR.* Sir,-The following observations might with propriety have formed part of a communication which you did me the honour of inserting in Number 1190 of this Magazine. But, as I prepared that paper somewhat hastily, you will perhaps excuse my troubling you with these additional remarks. Although unwilling to propound results without the calculations on which they are founded, yet I venture to give a more general case of the proposition enunciated at page 405 of the above-mentioned number, viz. that the reduction of the general equation of the (2r)th and higher degrees to another of the same degree, in which the (r+1)th and (r+2)th terms shall be wanting, depends upon the solution of the general equation of the (r+2)th degree. This is an instance of the classification alluded to in my last paper. As I there intimated, I shall take a proper opportunity of discussing this and similar questions. The relation of the methods employed in detecting "critical" cases will also be a subject for consideration. It appears not unlikely that, by expressing such transformations as are ca * See the paper headed "Recent Mathematical Investigations on the subject of Equations," at page 404 of the last volume of this work, pable of it in terms of the function Φ (or ), alluded to at the bottom of page 406 of your last volume, we shall obtain a better view of the formulæ and difficulties involved in those transformations. May we not hence derive some assistance in endeavouring to ascertain, in any proposed case, whether the method marked (1) at page 404 of that volume be applicable or not? I shall perhaps be pardoned for offering here an instance which, while it affords an illustration of what is meant by an "illusory" result, may also as an example for exercise prove useful to those engaged in studying this subject, or that of symmetric functions which is intimately allied with it. The form taken by the second condition is not unworthy of attention. Adopting a problem attacked by Mr. Jerrard, let us suppose it required to reduce the biquadratic given at the second line of page 70 of his Mathematical Researches to another biquadratic of the binomial form, and, using the expression which results from making S=0 and UI in the value of y suggested at lines 8 and 9 of the ensuing page of that work, let us call the three equations of the problem (see pages 43, 46, 47 of the Researches) 0=A'B'C', then, from the condition A'=0, we obtain P=0. The equation B'=0 becomes, on developing, substituting for the symmetric functions their values in terms of C and D, and reducing, The above figures represent a method of enabling locomotives to ascend inclined planes on railways. A, fig. 1, is a metal drum with a solid screw thread, a b, carried round its circumference, which with its axle, B C, is fixed horizontally in bearings under the engine, and equidistant between the rails. The screw is constructed so as to rotate right or left by proper gear work connected with the fly-wheel of the engine, and the thread of it, a b, works into a sort of rack, though considerably modified, as will be presently explained. DE is a continuous length of very stout bar-iron, borne on supporters, F, which have their foundation in the rail sleepers, G. At fixed distances, corresponding with the thread of the screw, a b, the iron, D E, is perforated for the reception of vertical anti-friction wheels or rollers, d, the axles of which are carried into bearings in the sleepers below, as n, fig. 2. The rack runs parallel with the plane of the ground over which it is carried, at a height of from six to twelve inches, and midway between the rails. When the screw is made to rotate by the engine, the thread, ab, is brought into contact with the periphery of any one of the wheels, d, which revolves, and the whole of the screw and the drum, A, pass over it. Before the whole of the thread has passed one of the wheels, d, it has reached another, more forward; and thus it passes from one to another all along the line. It must be borne in mind that the action of the thread of the screw on the roller, d, is such that the parts of each are lifted from one another, which reduces the friction to a minimum, and is totally different from the action of a screw in most situations. Note also, that when the screw is not required it must be thrown out of gear with the rack, and also with the engine. By reversing the engine the screw acts in the opposite direction. Racks are only intended to be on those parts of the line that are inclined planes. Fig. 2, 9 g, are the lateral supports of the rack, the ends of which might be bolted to the sleepers, or, still better, carried under the rails on each side, and would not require to be of very stout metal. I am, Sir, respectfully, 172, Blackfriar's-road. July 2, 1846. |