Mr. C. W. Williams exhibited and explained the sight-tubes which he now used for the marine boilers of the City of Dublin Steam Packet Company's vessels. The instrument consists of a wrought-iron welded tube 2 inches diameter with a screwthread cut upon the exterior: it is inserted across the water spaces of the boilers and secured by means of nuts in such positions behind and opposite the furnace, as enables the engineer to see all that goes on interiorly, particularly the degree of perfection or imperfection in which the gaseous matter enters into combustion and the effect of admitting or excluding the air. The instrument had been found very useful not only in experiments but in practice on the large scale, and he deposited it in the Gallery of the Institution in order that it might serve as a model for those who were inclined to adopt it in marine boilers. May 31, 1842. "On the construction of Model Maps, as a better mode than Sectioplanography for delineating the Drainage and Agricultural Improvements of a Country, or projected lines of Railways, Canals, &c." By John Bailey Denton, Assoc. Inst. C.E. This communication was accompanied by a map in relief of an estate, as a specimen of the method which the author recommends. The subject of mapping in relief is not new, and the author had previously published a treatise on the subject,* but having made extensive experiments, he was enabled to bring the subject before the Institution in a more defined form, showing that the construction of the models had been reduced to a simple and cheap method. These models are peculiarly recommended for pointing out the capabilities of a district for drainage either for agricultural purposes, or for collecting waters together for manufacturing power. They are superior to maps, as they show at a glance the relative heights of the various points, display the geological phenomena, and may be made to delineate the state of cultivation of the districts. lines of railways, of roads, or of canals, can be more clearly defined upon them, and they are stated to be peculiarly adapted for parish surveys. The The expense of making a model of an estate of compact form is stated to be from two shillings and sixpence to three shillings and sixpence per acre. "Observations on the Periodical Drainage and Replenishment of the Subterraneous Outline of a Method of Model Mapping, by J. B. Denton. Weale, 1841. Reservoir in the Chalk Basin of London." By the Reverend James Clutterbuck, &c., &c. This paper, which formed the substance of a letter to the Reverend Dr. Buckland, and was by him communicated to the Institution, consists of a series of observations on the periodical drainage and replenishment of the subterranean reservoir of the chalk basin of London, especially that part of it which lies in a N.W. direction between London and the Chiltern Hills. The author divides the district into two portions, that to the north and that to the south of the river Colne. The northern portion is mostly covered only with a bed of gravel, through which the rain water percolates to the chalk, in which, being upheld by the retentive strata below, it accumulates until it finds vent by several deep valleys which incline southward, and carry off a large quantity of water by the streams Ver, Gade, Bulbourne, and Chess, into the river Colne, which runs in a S.W. direction under the escarpment formed by the outcrop of the London and plastic clays. The surface of this reservoir or the water level, regulated by these vents, dipping towards the south at an average inclination of nearly 300 feet in fourteen miles, may be represented by a line drawn from the upper district at that angle, and terminating at the river Colne. Α The southern portion is almost entirely covered by the London and plastic clays, from the surface of which the rain water flows in open drains and water-courses. considerable portion of that which flows towards the Colne, sinks into the subjacent chalk, when it arrives at the outcrop of the sand of the plastic clay formation, and assists in the replenishment of that portion of the reservoir that underlies the London and plastic clays. Here the water level, or the height to which it would rise through perforations in these clays, where its continuity is interrupted by them, would be represented by a line drawn from the Colne to mean tide level in the Thames below London, the only apparent vent for their waters. In the upper district, during the replenishment of the reservoir, which usually occurs between December and March inclusive, the water accumulates in a proportion increasing with the distance from the river or vent, and falls off in a corresponding ratio during its periodical exhaustion, which usually takes place between April and November. This alternation of level, which in the upper districts exceeds 50 feet in perpendicular height, would be represented by a line fixed at the river or vent, and rising at an angle proportionate with the increase furthest from it, the extent of its rise or fall being determined by the quantity of rain percolating the chalk. The ratio between these extreme points is so exactly maintained, that if the difference of rise or fall in two wells, one near, and another at a distance from the vent be ascertained, the alternation in the intermediate wells will be determined with considerable accuracy. The progressive rise of the water level is apparent at the sources of the streams which break out at higher levels in the valleys in which they run, or when brooks or burns burst forth and run during a certain period, when the surface of the reservoir attains a certain level, previously to which, the water rises in every depression till it reaches the height at which it can flow away; the converse of the effects which preceded their bursting may be seen as they cease to flow. When no water percolates the surface of the upper district, the flooding of the Colne by heavy rains, together with the sinking of the water into the chalk at the outcrop of the sand of the plastic clay formation, raises the level in that locality, and by checking the drainage retards the exhaustion of the reservoir. When this occurs during the replenishment, and from continued rain, the level near the river maintains an increased elevation, the water checked in its course towards its vent accumulates in a ratio increasing with its distance from it, a process of adjustment to be traced throughout the district during the replenishment, and conversely during the exhaustion of the reservoir. The geological condition of the lower portion of the district, together with the paucity of wells, make it difficult to ascertain the extent of the natural alternations of that part of the water level which underlies the London and plastic clays; the difficulty is increased by an unnatural depression caused by the exhaustion of water under London, which is said to increase yearly, and indicates that the rapidity of the demand exceeds that of the supply: the alternation at that point may be from 2 to 4 feet, and is coincident with the rising and falling of the levels in the upper district. If water be discharged from a shaft in the chalk by a power not capable of exhausting it entirely, the rapidity of the reduction of the level will gradually decrease until it is exactly balanced by that of the supply; when the exhaustion ceases, the level will rise in the inverted ratio of its reduction; if the level be measured in a line from the point of exhaustion, a similar reduction will be found, falling off at an angle decreasing with the distance from it. The aggregate discharge of water from under London produces a similar effect: daily measurements in one well, confirmed by some coincident measurements in another more than a mile distant, show that beginning on Monday, the level is gradually reduced during the week; the cessation of pumping on Sunday is marked by the rising of the level by Monday morning; if any great quantity of rain falls, a sudden rise or check in the periodical fall takes place; the resumption of any extensive or continued discharge of water may be traced; a general coincidence of rise and fall in different wells is apparent; holiday times, such as Christmas, Easter, and Whitsuntide, may be distinguished. Thus, the measurement of a chalk well in London would show the days of the week and the great festivals, by the daily variations; the seasons would be indicated by the average difference in the height of the level at different periods of the year; and the changes of the weather by the falling of rain, would also be shown. The chalk under London is of a much closer nature than that in the upper districts; it yields the water sparingly but steadily from orifices beneath those beds or bands of flint which are the most unbroken and the strongest, and from faults and cracks which are frequently met with. The constant and increasing demand not only depresses the level under London, but must accelerate the exhaustion of the reservoir above. When the water level near the Colne is suddenly raised by heavy rains, a simultaneous effect is produced on the chalk wells in London. This suggests the possibility of connecting a periodical defalcation of water observed in that stream, and the river Lea on Monday, at those seasons when the water is short, with the exhaustion of water under London. The courses of both these streams is somewhat similar with reference to that place, though they flow in opposite directions. There is some evidence in favour of this supposition, which may be established when more information is obtained, which will be best effected by keeping registers of the daily variations of wells in different localities, and determining the height at which the water stands with reference to Trinity high-water mark. Such information, if brought together, would well repay the labour bestowed on its collection. The author's views were illustrated by a number of sketches and enlarged diagrams of the geological formation of the district, &c. Dr. Buckland was desirous to bring the subject of Mr. Clutterbuck's paper before the Institution, because he was impressed with the value of a systematic series of observations upon a matter so intimately connected with engineering as the theory of the causes of the supply of water to springs and rivers, and the rise of water in Artesian wells. In his Bridgewater Treatise, pl. 68 and pl. 69, he had illustrated by diagrams the causes of the accumulation of a subterranean reservoir consisting of sheets of water diffused through strata of gravel, sand, and chalk within the basin of London, and of the rise of water in wells and small perforations through the London clay, under the influence of hydrostatic pressure. Mr. Clutterbuck's observations and experiments confirmed the general opinion, as to the existence of these subterraneous sheets of water in the chalk basin, and indicated a connexion between their distant parts, by the sympathy he had observed between the sudden floods at Watford and certain wells in London, the level of which had been carefully observed, and found to rise a few hours after the occurrence of the floods at Watford. In London, also, he had confirmed observations already made upon deep wells at considerable distances from one another, and found that any large quantity of water taken from one well reduced the level of those adjacent. It had been questioned whether the communication between wells of this kind took place solely through the medium of large cracks and fissures, or whether the entire masses of the permeable strata, beneath the level of the lowest springs which flowed from them, had all their pores and minutest interstices so entirely filled with water, that any abstraction of this fluid from one well was more or less rapidly replaced by a general flow towards it from every part of the water-logged stratum of sand, or gravel, or stone, in which it was excavated! on the latter hypothesis, during such a flow, the surrounding wells would be affected in the direct ratio of their proximity to that from which large quantities of water were taken. It had been found at Brentford, that, as the number of Artesian wells increased, the force and quantity of each became diminished; a similar effect followed in the case of adjacent wells in London; the inference he would draw, therefore, was, that a very extensive supply for the metropolis could not be obtained from deep wells of this kind, although a few wells might be supplied abundantly. The district called the London Basin is made up of a continuous seam of chalk, from 300 to 500 feet in thickness, which on the S.E. of the Colne is covered with beds of sand and gravel, alternating with plastic clay, and over all these, a thick covering of London clay whilst the country N. and N.W. of the Colne is for the most part composed of naked chalk. Beneath the whole chalk basin lies a sub-stratum of clay or gault which is impermeable by water, and upholds the reservoir in question. The valleys in this chalk are traversed by the rivers Ver, Gade, and Chess, whose chief perennial supply of water is from springs that issue out of the chalk; in one of these valleys Mr. Dickinson had proved by experiments made with Dalton's rain-gauge (which, being buried 3 feet beneath the surface, received only such water as descended more than that depth) that during about two-thirds of the year the rain which fell rarely sank 3 feet into the earth; but in November, December, January, and February it passed down into the subjacent chalk, in proportions which accorded so constantly with the greater or less amount of rain falling in these four wet months, that he had been accustomed to regulate the amount of orders undertaken to be executed in his paper-mills during the following spring and summer, by the indications on this rain-gauge, of the quantity of water that descended more than 3 feet in the preceding winter. The The Colne is often flooded by the effect of sudden rain which is retained upon the surface of the London clay; but that portion of its water which is derived from perennial springs is supplied from the overflowings of the natural reservoirs, or substerranean sheets of water which fill the interstices of the chalk, and also of the sand and gravel beds of the plastic clay formation. surface of this reservoir is marked by the outbreak of a succession of springs, at levels gradually rising as they are nearer to the upper regions of the chalk; and as the entire supply of this subterranean stock of water is derived from rain that falls on the surface of permeable strata within the London basin, the abstraction of water from any part of this reservoir would, Dr. Buckland conceived, diminish the quantity remaining to be discharged by springs into the rivers in the vicinity of such abstraction, by the total amount of water so transferred to any other than its natural channels. It was asserted that the surface of the water in this subterranean reservoir did not maintain a horizontal level, but that it rose nearly 300 feet in fourteen miles, between the town of Watford and the highest spring that issued from the neighbouring chalk hills. The molecular attraction of the particles of chalk through which this sheet of water is diffused, and the obstruction presented by friction to its descent through the numerous pores and minute crevices by which it has to pass in adjusting the line of its upper surface, might account for this deviation from the level line which fluids assume, if left to act freely in open spaces, or in large and continuous conduits; Mr. Clutterbuck's repeated observations upon wells along the line in question must be considered to have proved the existence of this inclined level. His observations were also very important, as to the floods at Watford raising in a few hours the level of the water in deep wells in London, and as to the effect of a steam-engine erected to pump water from a large experimental well near Watford, in lowering the water in smaller wells in that town and the country adjacent to it. Mr. Dickinson had made very accurate observations upon the absorption of water by the chalk, and was convinced of its being always in a wet state almost amounting to saturation; but few crevices and fissures exist in the chalk of the district under notice; the rain therefore occupies a considerable time in overcoming the molecular attraction of the particles through which it passes. Wherever fissures exist at a certain depth below the chalk, they become channels which collect and facilitate the flow of water to maintain the springs; the accumulations of the winter rain sink slowly down in summer, and by a series of vents or springs furnish a supply for the rivers which run in the deepest valleys of the chalk district; a long cessation of rain lowers the level of the water in the rivers, at an interval of some months after the drought, and any extraordinary demand by pumping from the wells in the chalk, would lower the water in the wells around, even at a considerable distance. From experiments with the rain-gauge buried 3 feet below the surface, he found that but little rain penetrated to that depth until the months of November, December, January, and February-the total quantity per annum was shown to vary between 17 inches and 6 inches, which latter amount sufficed to fill the principal springs., He was induced to believe that if a large supply of water was drawn from the chalk it would eventually have a prejudicial effect in diminishing the water in the rivers of the district. Mr. Clutterbuck said that the sphere of his observations extended over a line of wells 20 miles in length, and in the whole of them there was the most perfect accordance between the alterations of level of the water and the indications of the rain-gauge, allowing the time necessary for the rain to sink into the chalk,-as also there was between the fall and replenishment of the wells at Watford and those in London, whence large quantities of water were obtained by pumping;-he could always tell by measuring the height of water in one well of the series, what would be that of any other well along 271 the line: he therefore was satisfied of the accuracy of the observations in his paper. Mr. Dickinson observed, that he could not satisfactorily account for the greater amount of variation in the wells at the higher part of the district, when compared with those of the lower part-the alternations of the former amounting frequently to 30 feet, while those of the latter were only 10 feet in the same time. Dr. Buckland believed this fact to arise from the hydrostatic pressure being less interfered with by friction and capillary attraction, in the lower part of the district, than in the upper part. Mr. Clutterbuck accounted for the alternations of level in the sand springs, being greater than in the chalk springs, by the relative degrees of opposition the water met with, from the friction in passing through the two kinds of strata. A member observed that the brewers of London could be supplied by the water companies at a cheaper rate than by pumping, but as a large quantity was used for refrigerating the wort, it was important to have the water at a low temperature, they therefore were obliged to pump it up at a great expense. The quantity raised at Messrs. Reid's well was about seven thousand seven hundred barrels of thirty-six gallons each per day, which was calculated to be a sufficient supply for five thousand families-there was already a decided diminution manifested in the supply from the sand springs, and an extension of these effects might be anticipated from the sinking of any large number of wells into the chalk. Dr. Buckland ascribed the difference of the supply of water in sand springs, and in those originating in chalk, to the relative extent of surface of the sandy and cretaceous strata in Hertfordshire, by which alone they receive their respective supplies of rainwater, the amount of sandy surface being to that of naked chalk about as one to twelve. The rain filters more rapidly through the sand, than through the chalk. In beds of hard and compact chalk at great depths, the water sometimes finds no passage except through occasional fissures, but where the chalk is soft, loose and fragmentary, it percolates rapidly. In the deep well now sinking near Southampton, through London and plastic clay into hard and solid chalk, it would probably be necessary to continue the boring or excavation down into some loose and more permeable stratum below the chalk, before any very large supply of water would be obtained. Mr. Palmer directed the attention of the meeting to the account of the wells in the London Basin, given in Conybeare and Phillips's Geology, (book 1, chap. iv. sect. 11.) It is there stated, that at Tottenham, which is about 70 feet above high-water mark, after boring through 123 feet of clay, and 2 feet of calcareous sandstone rock, the water rose to within a short distance of the surface in a few hours. At Epping, where the summit of the well is 340 feet above highwater mark, the extreme depth of the bore was 420 feet, but it was abandoned because no water was found; at the end of five months the water rose to within 26 feet of the surface, and it has so continued, at 314 feet above high-water mark. These recorded facts induced him to reIceive with much caution the statements in Mr. Clutterbuck's paper, especially since he doubted the ready flow of water through the chalk by which the sympathy between the various wells was demonstrated: he had found that chalk might be used as a good puddle for holding water, and therefore as it was certainly more compact when in situ than when it had been worked, unless the water flowed along the faults and the beds of flint, he could not understand how it passed so rapidly as had been stated. The chalk no doubt contained some water, but if it was saturated why did not the water in all the wells assume one uniform level instead of heights varying between 20 feet and 314 feet above high-water mark? NOTES AND NOTICES. Castor Oil Candles-Are manufactured in Philadelphia, and said by the American papers to be equal to wax, but not so cheap. The Boccius Light.--A new light opposite Northumberland House, in the Strand (called the Boccius light, after the name of its inventor), was exhibited for the first time on Wednesday evening, and fully answered the expectations which had been formed of it by the scientific and practical gentlemen who had previously had opportunities of inspecting its qualities. It is supported upon six pillars of wood, joined at the top in the shape of a Bourbon crown, and irradiates the entire space between the Post-office and Cockspur-street, the Strand beyond Craven-street, and as far as St. Martin's Church on the north. Nelson's Pillar, with its scaffolding, in Trafalgar-square, appeared as if standing out in broad moonlight, and the gaslights surrounding the statue at Charing cross were extinguished, as useless, except on the shadow side towards Whitehall. The establishing of this brilliant lamp on a site where the throng of foot-passengers and carriages is so dense and incessant from the intersection of four such great, streets will be of considerable advantage on dark winter nights, particularly to persons having business at the Post-office, as the smallest print or writing can there be distinctly read with ease. The light has a most imposing ef fect; it is very large, and though peculiarly white and soft, and free from all quivering and unpleasant effect on the eye from its intensity, it is so exceedingly powerful that it is impossible to look at it even for a second of time. It is understood that Mr. Boccius's invention is equally applicable to burners of the smallest as well as of the largest size; and that this increased brilliancy of light is obtained with a great economy of gas, but at what expense has not, we believe, been stated. For the purpose of public illumination the effulgence of this lamp must be acknowledged greatly to excel all others yet produced.-Observer. [The specification of this most extravagantly-lauded invention will be found in our 994th Number, and by referring to that, the reader will most probably be a good deal puzzled to discern the why and wherefore it should be The so much better (as alleged) than others. gas is supplied from a number of concentric rings, perforated with a vast number of small holes on their upper surfaces, but this is precisely the plan adopted by Mr. Gurney in what he calls the Bude Light. Instead, however, of one chimney, as usual, the Boccius Light has two chimneys, one within the other; and so far, certainly, there is novelty: but novelty of a strange sort, whereas it has been generally considered advisable that the chimney of a lamp should cast as little shadow as possible, the second chimney of the Boccius lamp is made of solid metal, and casts a darker and deeper shadow than any we ever saw. Our present impression of this new wonder of the day is that what is good in it is not new, and what is new is not good.-ED. M. M.] Steam Voyage through France to the Mediterranean. The following extract from a Leghorn letter or the 10th August appears in the Times :-"Yesterday three steamers arrived here. They came from England, and made their voyage through France, for they first ascended the Seine, and then passed by the way of the canals into the Mediterranean. This is the first voyage of the kind that ever was made. These steamers are small iron boats made for the Papal Government, and destined as tugs for the Tiber, to tow merchant ships up the river. They sailed again yesterday evening for their destination." Meteoric Stone.-Dr. J. Magill (of Cookstown) has communicated an accountof a phenomenon that occurred in Harrowgate on the 5th inst., from which it appears that at five o'clock, p.m., during a heavy squall, accompanied by vivid flashes of lightning, from the south-east, some persons at work in draining the common in High Harrowgate, heard a hising sound in the air, and almost at the same moment observed a dark object falling at a short distance from them, which, on examination, proved to be a large aerolite, orjmeteoric stone, similar to those which fell a few years since near Cardiff. On examining it the following morning, in company with Messrs. Thompson, J. M'Caw, and J. Montgomery, they found it had the same appearance as the basalt of the Giant's Causeway, with this extraordinary difference, that it is interspersed with small particles of silver or flint, and what geologists term album Grecum, or white Greek stone. The men who first saw it state that "it was warm to the touch," but the Doctor doubts that such was the case. It weighs about half a ton.—Mining Journal. INTENDING PATENTEES may be supplied gratis with Instructions, by application (postpaid) to Messrs. J. C. Robertson and Co., 166, Fleet-street, by whom is kept the only COMPLETE REGISTRY OF PATENTS EXTANT form 1617 to the present time). LONDON: Edited, Printed, and Published by J. C. Robertson, at the Mechanics' Magazine Office, |