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THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



Febbuaby, 



piers, two of which consist of a single row, and two of a douhle row of piling, 

 forming three spans of fifty feet each, and having about eight feet headway 

 under them at high water. The floating harge, or dumby, on which the pas- 

 sengers land, is one hundred feet long and twenty.five feet wide, rising and 

 falling with the tide, in grooves at each end, formed by piles and protected by 

 dolphins. Tlie connection between the damby and the pier is by a moveable 

 stage eight feet wide and fifty feet long, secured to the pier head, at one end 

 by a binge joint, and the other end similarly connected to a flight of steps on 

 wheels, which moves on a tramway fixed to the deck of the barge. The 

 principal portion of the timber used in its construction was fir; but the whole, 

 whether of fir or oak, was impregnated by Payne's process — those portions 

 below high-water mark being further protected by a coating of Stockholm 

 tar. Tbe whole of the cast and wrought iron work was galvanised. 



The Corporation of London had observed the necessity for an improved 

 landing place, so early as 1841, Imt it was not until a fatal accident occurred 

 in 1844, that any decided steps were taken in the matter: then Messrs. 

 Walker and Burges received instructions to prepare a design, which was 

 approved, and the pier was commenced in March 1845, and completed in 

 October of the same year, under the superintendence of Mr. Hewett, M. Inst. 

 C.E. The total cost 'was about 4,000/. 



The next paper read was a "Description of a Timber Bridge, erected 

 over the River Ouse, on the line of the Lynn and Ely Railway." By Mr. J. 

 S. Valentine, M. Inst. C.E. 



The total length of this bridge was four hundred and fifty feet, divided 

 into eleven hays, ten of thirty feet span each, and one over the river of one 

 hundred and twenty feet span on the square, and one hundred and twenty- 

 one feet six inches on tbe skew. This river-opening consisted of three 

 laminated timber bows, resting upon stone piers, the material for which was 

 procured from the New Leeds Quarries. The dimensions of the bows were, 

 length of chord, one hundred and twenty-one feet six inches ; versed vine, 

 fourteen feet two inches ; and their depth, three feet eight inches ; the width 

 of the outer bows was two feet two inches, that of the centre bow two feet 

 nine inches. They were formed of fifteen layers of three inch deals, abutting 

 upon a cast-iron plate, bolted to the tie-beams, which consisted of two whole 

 timbers scarfed and bolted together. Each tie-beam was suspended from the 

 bows by thirteen wrought-iron rods, two inches in diameter, and between 

 these diagonal struts were fitted. Transverse joists, notched on to the 

 tie-beams, extended across the whole width of the bridge, and on these the 

 rail bearers were laid, the intervening spaces being filled with three inch 

 deals, laid longitudinally. 



The works were commenced in the autumn of 184C, and completed in 

 October 1847; the total cost of the superstructure being about 3,744?. 

 When tested, by placing three locomotive engines on each line of rails, the 

 total deflection was only three-eighths of an inch. 



Jan. 22. — The paper read was "On the Periodical ^Alternations and Pro- 

 gressive Permanent Depression of the Chalk Water Level under London." 

 By the Rev. J. C. Clutterbuck. 



The author began by defining the Chalk Water level to be, "the height lo 

 which the water rises at any point or continuous series of points m the 

 chalk, or from the chalk in perforations, through the London and plastic 

 clays, above the chalk." The term 'Artesioid' was used to describe those 

 wells sunk through the London and plastic clays, in which the water rose 

 from the chalk, or the sands of the plastic clay formation, above the level of 

 those strata, though it might not rise to, or overflow the surface of the 

 ground. 



Reference was made to papers read before the Institution in 1842 and 

 1843, in which it was sliown that the chalk water level was described by an 

 inclined line drawn from the highest level at which the water accumulated 

 in the chalk, to the lowest proximate vent, or outfall : a general rule, which 

 was found to hold good, not only where the water was found by sinking into 

 a permeable stratum, but where, as in the London Basin, the water rose from 

 a permeable stratum, through perforations in any impermeable stratum 

 above it. 



The example treated of in the paper, was described by a line inclining at 

 an average of about 13 feet in a mile, from the outcrop of the London and 

 plastic clays, to mean tide level in the Thames, below London Bridge. 



The height to which water rose in the Paris Basin, from the lower green 

 sand, was adduced in confirmation of that rule. Before tbe artesian well 

 at Crenelle was bored, M. Arago calculated, that the water would rise above 

 the level of tbe soil at Paris, as it rose above that level at Elbeuf, near Rouen. 

 The height at which the water was found in the lower green sand, near 

 Troyes, being 100 metres above Paris, and 131 metres above the sea, tbe 

 author found that a line drawn from that point, to the level of the sea at 

 Havre (where the green sand cropped out), passed over Paris and Elbeuf at 

 the elevation to which tbe water actually rose in both places. A calculation 

 based on the same principle (taking the level of the water in tbe lower 

 green sand, at Leighton Buzzard, at 280 feet above the sea), showed that if 

 the chalk and gault were bored through in London, the water from the 

 green sand would rise 150 feet above Trinity high-water mark. 



Passing from the natural to the actual condition of the chalk water level, 

 under London, there was a general permanent depression of from 50 to 

 60 feet helow Trinity bigb-water mark. Measurements of a well in London, 

 is which the level was seldom disturbed, showed periodical alternations, 



coincident with tbe exhaustion and replenishment of the chalk stratum by 

 natural causes, to tbe amount of 4 ft. 6 in., and a permanent depression of 

 1 ft. 6 in. per annum, or 12 feet in eight years. 



Again, referring to former calculations, it was shown that the margin of 

 this depression was extending in a greater ratio towards the North than to 

 the South, or S.E. Since 1843, the level was permanently depressed at 

 Hampstead-road, 10 feet; Camden Town, 19 feet ; Kilburn, 20 feet; and 

 Cricklewood, 10 feet. The limit of the depression being, in 1843, between 

 the latter places. 



Allusion was then made to the influx of water at the point where the 

 Thames passed over the outcrop of the sands of the plastic clay formation, 

 and the chalk, as a point to be determined by geological inquiry, and con- 

 nected with observations as to the action of the tides on the level, and the 

 chemical quality of the water, in that neighbourhood. 



The general conclusion drawn from all these facts was, that the rapidity 

 of exhaustion from Artesian wells under London, greatly exceeded the 

 rapidity of supply ; that the amount of defalcation was marked, and could 

 be measured by the extension of a progressive permanent depression, proving 

 that the supply of water from the chalk stratum became each year more 

 precarious, and less to be depended upon, even should there be no addition 

 to the Artesioid wells in and around the metropolis. 



In the discussion which ensued, it was shown that only such a supply of 

 water percolated annually through the chalk stratum, as could be accounted 

 for by the discharge from the rivers of the upper district. The results 

 yielded by Daltou's Rain Gauge, as used by Mr. John Dickinson, were 

 adduced in proof of this position. 



The chemical analysis of water from wells sunk into the chalk, showed 

 the probability of an influx of the tidal water of the Thames, to replenish 

 the vacuum caused by the immense extent of pumping from the London 

 wells. 



On the other hand it was contended, that from the great extent of surface 

 whence the chalk derived its supply, there might be such a surplus store of 

 water, as would warrant any amount of pumping, for the domestic supply 

 for the metropolis. 



ROYAL SCOTTISH SOCIETY OF ARTS 



Dec. 10, 1849.— Thomas Grainger, Esq., C.E., President, in the Chair. 

 The following communications were made: — 



1. The President delivered an address on the desirableness of obtaining 

 communications relative to the Construction and Details of Engineering and 

 other PubUc M'orks, accompanied by the necessary Models and Drawings. 



2. "\otice of a Chromatic Stereoscope." By Sir David Brewster, 

 K.H., r.R.S , V.P.R.S.E. 



The instrument consists of one lens 2* inches in diameter or upwards, 

 through the roargin of which each eye looks at an object having two colours 

 of different refrangibility. The effect of this is to cause the two parts of 

 the object thus dift'erently coloured, to appear at different distances from the 

 eye, just as in tbe Lenticular Stereoscope, the two parts of an object that 

 are nearest to one another in the double picture rise in relief, and give the 

 vision of distance as of a solid figure. The instrument may consist of two 

 semilenses, convex or concave, or of two prisms with their refracting angles 

 placed either towards or from one another; and the effect is greatly increased 

 if the lenses or prisms have high dispensive powers, such as flint glass or oil 

 of cassia. 



NOTSS OF THE MONTH. 



RAILWAYS OPENED IN THE YEAR 1849. 



The aggregate length of English railways opened for traffic in the year 

 1849 was 750 miles; of Scotch railways 731 miles, and of Irish railways 

 111 miles — making the aggregate length of railways opened in the United 

 Kingdom during the past year 937 miles, being 270 miles less in extent than 

 those opened during the year 1848. 

 The English lines were— 



Chester and Holyhead, Mold branch, 13J miles. 



East Anglian, 24 miles. 



East Lancashire, 45 miles. 



Eastern Counties and Norfolk, 15 miles. 



Eastern Union, including the Stour Valley line, 43 miles. 



Furness, 171 miles. 



Great Northern, 33 miles. 



Great Western extensions, 30 miles. 



Laitcashire and Yorkshire branches, 12 miles. 



Leeds and Thirsk, 30 miles. 



London and Blackwall, 1 J mile. 



London and North-Western (Huddersfield and Manchester, and Leeds and 

 Dewsbury), 44 miles. 



London and South-Mestern branches, 22| miles. 



Manchester, Buxton, Matlock, and Midland, 12 miles. 



