IS40.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL 



2*^3 



BBsistance oiiposed by the jji^essiire and friction. lu making comparisons 

 between tlie common water-works engine and tlie Cornisli, tliis was the 

 mode lie had adopted, and he ijeUeved it to be tl.e only fair one. He liad 

 pi-oved the aecnracy of the mercurial gauges by the measurement of the 

 column of water supported. The Cornish engine at Old Ford acts by raising 

 a weight of metal, which, upon its return, raises the water. This is the only 

 engine in Loudon of the kind, and to establish a comparison between it and 

 any other pumping engine, it is only requisite to ajiply a mercurial gauge as 

 just described to the pump of each, and whether the water is lifted dkect or 

 forced through any length of pipes, the resistance or load against wdiich the 

 steam acts will be shown. Previously to his Cornish engine being set to 

 work, the beam and plunger were balanced with the greatest accuracy, and 

 their preponderance ascertained before the steam piston and plunger were 

 packed. The weight afterwards added to the pump end was also carefidly 

 ascertained. The weight raised at each stroke of the engine is thus accu- 

 rately known. The number of strokes performed in a giyen time is regis- 

 tered by the counter. The coals are carefully weighed. By ordinary atten- 

 tion, the boilers are so managed with regard to the work to be done, that no 

 steam is allowed to blow away, whether the engine l)e maldng 3 or 9 strokes 

 per minute ; and in calculating the dnty done by the quantity of coal con- 

 sumed, no deduction is made for stoppages. Thus, a certain number of 

 strokes being made, a known weight has lieen raised to a given height a given 

 iiuml)er of times by the consumption of a known weight of coals. This 

 engine worked under the pressure of a column of water from 110 to IIG feet 

 in height, and the water was forced through 300 miles of pipe, varying from 

 42 inches to 3 inches in diameter. The load at the pump in the common 

 pumping engine is ascertained by the same means, and no error can exist in 

 determining the duty performed by each. 



Mr. Parkes observed, that the term duty did not seem to be quite under- 

 stood ; duty was not the weight of water raised 1 foot in height, but that 

 weight divided by a bushel or other measure or weight of coals also ; that 

 the time in which the water was raised did not enter into the computation of 

 duty, though it did into the determination of horse power. He would again 

 call attention to the fact, that coal was no measure of power or of the qnality 

 of an engine ; that one engine might be doing more duty than another, be- 

 cause it had better coal or better boilers ; and that the only standard of per- 

 fection between different engines was the relative consumption of water as 

 steam for equal effects. 



Feb. 11. — The President in the Chair. 



The following were balloted for and duly elected : — John Green, John 

 Hartley, as ilembers ; Joseph Woods, Frederick Rumble, as Graduates ; Oli- 

 ver Lang, John Grantham, Capt. George Smith, R.N., Lieut. E. N. Kendall, 

 E.N., as Associates. 



"A Description of the Coffre Dam at the site for the neto Houses of Par- 

 tiament." By Grant S. Dalnmple. 



The works described are those which necessarily precede the erection o' 

 the main building. They consist of the coffre dam, river wall, and the foun- 

 dations of the river front— according to the designs, and under the direction, 

 of the engineers (Messrs. Walker and Surges) and Mr. Barry, the architect ; 

 the whole being executed by Messrs. Lee, tlie contractors. 



The mud at the site of the works varied much in depth and in consistency, 

 but beneath it is a bed of red gravel and sharp sand, averaging 14 feet in 

 tliickness, laying over a stratum of stiff clay, into which the piles are driven 

 to a depth of 2 feet. To faciUtate the driving of the piles, a curved trench, 

 27 feet wide by 8 feet deep, was dredged in the line of the dam. The main 

 piles of Memel fir, 36 feet long by 1 foot square, were then driven, leaving 

 their tops 4 J feet above the Trinity high-water mark of ordinary spring tides. 

 The waling pieces were then attached, and the outer sheet piles of whole 

 timber, 30 feet long by 13 inches sqnare, sawn square on all sides, so as to 

 ensure the joints being close when driven and bolted to the waling. The 

 inner sheet piles of half timlier w-ere then driven to the same depth as tlie 

 others ; the space above them was made up with liorizontal pieces, bedded 

 down to them, and secured with bolts to the furring pieces inserted above 

 the waling at each gauge pile. The whole length of the dam was secured 

 by diagonal braces, extending back to the old river wall, agauist which they 

 were ainitted. The outer and inner rows of piles were secured together by 

 three rows of WTOuglit iron bolts, the lower being 2 J inches diameter, and 

 the two upjier rows 2 inches diameter. The whole of the piles being driven, 

 the space between was cleared out down to the day substratum, and then 

 filled up with stiff clay mixed with a portion of gravel ; a portion of the 

 excavated matter was then laid on both sides of the dam to protect the 

 piling from injui-y. 



The first pile was driven on the 1st of September, 1837, and the dam was 

 closed on the 24th of December, 1838. The extreme length of the coffre 

 dam along the river face is 920 feet, and the ends return at an angle until 

 tliey meet with and enter the old river wall, at a distance of about 200 feet 

 from the face of the dam. 



The excavations for the foundation of the river wall were got out in lengths 

 of 50 feet, levelled to receive the footing courses, which were laid on a bed 

 of concrete of a thickness varying from 1 foot at the north end to between 

 5 and 6 feet in the centre and south corner, where the substratum was loose 

 and spongy. The concrete was composed of C measures of gravel and sand 

 to 1 of ground lime from the lower stratum of the chalk formation. Along 



the face of the wall was driven a row of elm sheet piles, from 8 to 12 feet 

 long by 8 inches thick, square sawed, so as to drive close, spiked to an oak 

 wale, and the whole secured to the front by 1-inch wrought iron bolts, placed 

 at distances of 4 feet apart, stretching back 6 feet into the wall, and fixed by 

 cast iron washers bedded between the footing courses. The two bottom or 

 footing courses of the wall are 11 feet wide, of York landing, 6 inches thick ; 

 on these are two courses of Bramley-fall stone, each 1 foot 3 inches thick, 

 from which rises the stone facing of the wall, of Aberdeen and Cornish 

 granite, in courses vaiying in thickness from 2 feet 2 inches at the bottom 

 to 1 foot 7 inches at the top. The front is built to a curve of 100 feet 

 radius, and is backed with brickwork, maldng the total thickness of the wall 

 7 feet G inches at the bottom, and 5 feet at the top. Counterforts, projecting 

 3 feet 4A inches by 3 feet 9 inches wide, occur at intervals of 20 feet along 

 the whole length. At a distance of 28 feet 9 inches from the back of the 

 river wall is the foundation of the front wall of the main body of the bnild- 

 ing, the space between the two walls being filicd up with concrete, composed 

 of 10 parts of gravel to 1 part of ground lime. The total length of the river 

 wall, at the present level of 2 feet 3 inches above the Trinity standard of 

 high-water mark, is 876 feet 6 inches. The wings at each end, projecting 

 2 feet 3 inches before the face of the centre part, are 101 feet 6 inches long 

 each, leaving a clear teiTace walk, G73 feet 6 inclies long by 32 feet wide, 

 between the mugs and fronting the river. The height of the wall from the 

 bottom of the footing courses is 2.3 feet 9 inches. 



The excavation for the wall was commenced on the 1st of January, 1839, 

 and the building of it was commenced in March of the same year. The 

 amount of tiie estimate for the dam and waU was £74,373. 



" Oil Browne's Patent Hydraulic Level." By A. T. Hemming. 



This instrument, designed for ascertaining the relative heights of points 

 not visible from each other, consists of le;igths of water-tight flexible tubing, 

 attached to eadi other by brass joints, and having glass vessels at each end. 

 The vessels and tubing being nearly filled with water, the level of the water, 

 as seen in these vessels at two points whose relative heights are to be com- 

 pared, will serve to indicate their positions, whatever may be tlie inflexions 

 of tlie tubing betwixt the two vessels. Graduated rods are ]>laced perpen- 

 dicularly at the points of observation, and the lower vessel is raised, and the 

 higher lowered, until the level of the fluid therein intersects the graduation 

 of the rods. It is conceived that this level may be peculiarly useful in mines 

 and excavations, and in fixing complicated machinery. 



Light for Light-houses. 



Captain Basil Hall briefly explained his views as to obtaining for light- 

 houses all the advantages of a fixed Ught by means of refracting lenses in- 

 revolution. 



Tlie difference between a fixed and a revolving light is much in favour of 

 the revolving light, as the light can be concentrated and great brilliancy ob- 

 tained on any particular point at each succeeding flash ; — by a fixed light 

 being meant one in which the light is visible on every side ; and by a revolv- 

 ing light, one in which the light appears in periodical flashes. Fresnel's fixed 

 hght has only one-sixth the brilliancy of his revolving light. Fresnel's system 

 consists in having a large central lamp with four concentric wicks, surrounded 

 by eight lenses, each three feet diameter. The light is thus concentrated 

 and thrown off in eight pencils, which, as they strike the eye successively, 

 have very brilliant eftect, and are visible at a great distance. 



Captain Basil Hall's inquiries have been directed to ascertain whether the 

 well-known superior brilliancy of a revolving light could not bs obtained for 

 a fixed or continuous light ; that is, for one equally visilde in all directions 

 at the same moment. His idea was, that by giving a certain velocity of re- 

 volution to a series of lenses round a fixed light, as in Fresnel's arrangement, 

 a continuity of illuminating powei-, equal almost in brilliancy to that of a 

 slowlv revolving light, might be produced. This, he expected, would prove 

 true, provided no intensity were then lost. He had erected some apparatus 

 at the Towel', and determined the effect by experiment. The apparatus con- 

 sisted of a fixed central light with a scries of eight lenses, 1 foot diameter 

 and 3 feet focal distance, so arranged as to revolve at any velocity up to 60 

 revolutions per minute. The light from the central lamp being concentrated 

 by refraction through the eight lenses into eight pencils, having a divergence 

 of aliout 8° each, illuminated not quite 50° of the horizon when at rest ; but 

 when this same svstem of lenses was put into rapid motion, every degree of 

 the 360' of the horizon became illumined, and to spectators placed all round 

 the horizon, the light would ajipear continuous and equally brUliant in every 

 direction. The oiilv question would be, whether or not this continuous hght 

 is essenfiallv less intense than the light seen through the lenses at intervals 

 wdien in slow motion. The fact is, that two chsfinct efl'ects are produced in 

 this experiment— a phvsical eft'ect in diminishing the brilUancy of the light 

 exactly in proportion to the I'afio of the dark portion of the horizon compared 

 to that of the enlightened portion, viz. as 310^ to 50" ; and a physiological 

 effect (suegested bv Professor Wheatstone), l>y which the sensibility of the 

 retina mi"ht be so'excited liy a succession of bright flashes, that not only a 

 continuity of light might be 'produced, but a light not much, if at all, inferior 

 in intensity to th,at caused by the lenses at rest. When first set in motion, 

 the effect is that of a series of brilliant but tremblmg flashes ; as the system 

 of lenses is accelerated in velocity, the steadiness of the light increases with 

 scarcely any apparent diminution of brilliancy. At 44 revolutions per minute 

 absolute continuity is produced, and at 60 revolutions neariy the steadiness 

 of a fixed light, yfhen viewed from the distance of half a mile, the effect is 



