1842.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



385 



The rain filters more rapidly thro'.igh 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 con- 

 tinue 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 

 ro 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 high-water mark, the extreme depth of the bore was 420 feet, 

 but it was abandoned because no water was found ; at tlie 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 receive with much caution the state- 

 ments 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 sifu than when it bad 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 varving between 20 feet and 314 feet above high- 

 water mark ? 



Mr. Clutterbuck contended that the main points of bis statement were 

 borne out by Mr. Braithwaite's experience at Messrs. Keid's well. A clear 

 distinction must be drawn between the water derived from strata above the 

 clay and that from the chalk ; in some elevated spots near London, situated 

 like Hampstead, the clay is capped with gravel, which on being tapped, 

 yielded a supply of water ; at Stanmore the water from the gravel at the top 

 of the hill is u^ed ; and in a well sunk through the clay at the bottom of the 

 hill, the water stood at 140 feet below the surface, lie could not under- 

 stand why at Epping there should exist any variation from the usual observed 

 facts; the case deserved very careful examination, as it might arise from 

 some local cause. In the course of his observations upon the levels of the 

 wells in London, he found on one occasion that no depression occurred on 

 the Thursday which had hitherto always been the case ; he therefore sought 

 for the cause, and found that the Elstree reservoir had been opened on Wed- 

 nesday, June 1st, which satisfactorily accounted for what had occurred, as 

 from the diT state of the water-course not more than half the quantity of 

 water which passed from the reservoir, reached the river Colne, the rest sank 

 through swallow holes down into the chalk ; this showed the attention to 

 collateral circumstances, which was demanded in investigations of this kind. 



Mr. Frederick Traithwaite presented and explained a model of a well sunk 

 by him in the year 1841 at Messrs. lleid's brewery, in order to obtain water 

 from the chalk, which had become indispensable, in consequence of the 

 decrease of the supply of water from the sand spring. 



On examining the lower part of the well, whicii had collapsed in 1814, he 

 found that the dimensions of the cast-iron cylinder to be introduced, must be 

 limited to 5 ft. 3 in. by 3 ft. 2 in. ; it was commenced at the depth of 87 ft. 

 from the surface, and carried down 135 feet, to within 1 ft. 6 in. of the face 

 of the first bed of flints in the chalk. 



Being desirous of retaining all the water from the sand spring, he inserted 

 an internal cylinder which was sunk into the chalk at a depth of 138 feet 

 from the surface, thus eflfectually shutting out the sand spring from that of 

 the chalk, but permitting the former to flow to its accustomed level in the 

 space between the two cylinders; and to make this supply available in case 

 of need, cocks were inserted in the internal cylinders at convenient depths. 



He then proceeded with the excavation in the chalk, increasing the dimen- 

 sions at every foot in depth, until at 178 feet from the surface, the diameter 

 was 16 feet 6 inches ; the excavation was continued at that diameter to a 

 depth of 202 feet from the surface. 



In the progress of the work, water was found under the second, sixth, 

 eighth, and tenth beds of flints, and the total supply at this period was two 

 thousand barrels or seventy-two thousand gallons per day of twenty-four 

 hours. 



At 19G ft. from the surface the first tunnel was driven 91 ft. N. W. in the 

 direction of another well, which only increased the supply 400 barrels or 

 14,400 gallons in 24 hours. 



The eighth bed of flints, at 154 ft. from the surface yielding the largest 

 quantity of water, (300 barrels or 10,800 gallons per day,) he drove a second 

 tunnel 6 ft. high by 5 ft. wide, for 16 ft. E. to \V. and then N. and S. for 

 108 ft., by which he obtained an increase of 1500 barrels or 54,000 gallons, 

 per day. 



Having ascertained by boring, that a further supply of water could be ob- 

 tained at 20 ft. below, he continued the excavation 22 ft. deeper by 7 ft. di- 

 ameter, when be found water flowing from two horizontal fissures in the 

 chalk without flints ; at that depth he drove 2 tunnels, one N. W. connected 



with the first tunnel 91 ft. long, by which he obtained an increase of 3100 

 barrels or 121,600 gallons per day, the second tunnel in a S. E. direction 

 was driven for 24 ft., when he obtained a further increase of 800 barrels or 

 28,800 gallons per day. 



The total quantity of water thus obtained from the chalk, was 7700 

 barrels or 277,200 gallons per day of 24 hours, or 192 gallons per minute, 

 forming at the same time a reservoir in the chalk which could contain 

 100,800 gallon. 



lie stated the total expense to be under £7000 including the hire and 

 repair of temporary pumps, and the cost of two new sets of permanent 

 pumps. 



June 7. — The President in the Chair. 



" An Account oftlte Alieralians to Tullow Bridge." By Charles Forth. 



The old bridge at Tullow, over the river Slaney, was very dangerous from 

 its steepness, its narrow roadway (only 18 feet wide) and the awkward ap- 

 proaches to it ; alterations were therefore determined upon, for which the 

 author submitted a plan and also superintended the execution of it. The 

 floods forbade any diminution of the water-way, and it would have been in- 

 convenient to have raised the approaches on the low banks on either side, 

 flat arches of the following proportions were therefore decided upon. 



The inclination of the roadway was thus reduced from one in seven to one 

 in forty, wliile at the same time by adding to the abutments on the up-steam 

 side, the width of the roadway was increased from 17 feet to 23 feet, and by 

 completing a portion at a time, the thoroughfare over the bridge was not at 

 any time stopped. For the sake of economy, the work was done in un- 

 dressed rubble granite with an ashlar face, taking care that the stones abutted 

 well against each other, and on removing the centres, no settlement of any 

 importance took place, and the traffic of loaded cars weighing 35 cwt. each, 

 was carried on without any danger, within a week from the time the arches 

 were keyed. The expense of the alteration was only .€485, and it has stood 

 well although it has been subject to some heavy floods. 



A detailed drawing of the bridge, before and after the alterations, accom- 

 panied the paper, and Mr. Vignoles sent with it an enlarged plan, section, 

 and elevation for the purpose of more fully illustrating what he considered a 

 successful work. 



" On the Introduction of Letter-Press Printing for numbering and 

 dating the Notes of the Bank of England." By Thomas Oldham, Assoc. 

 Inst. C. E. 



The author commences by noticing the numbering press invented by Mr. 

 Bramah, and adopted in the Bank of England in the year 1809, by which 

 the expense and uncertainty of finishing annually a large number of bank 

 notes, with the pen, was materially diminished, and forgery was rendered 

 more difficult, although the machine was so far incomplete, that it produced 

 only units, the tens and hundreds requiring to be brought forward by hand. 



In that year (1809) the late Mr. John Oldham, (the father of the author,) 

 offered unsuccessfully to the Bank of Newry, a machine similar in principle 

 to that of Mr. Bramah, but with the additional power of efl'ecting numerical 

 progression, from one to one hundred thousand by its own operation. In 

 1813, these machines were adopted at the Bank of Ireland, and one of them 

 was subsequently attached to each press for printing the body of the notes, 

 in order to register and check the number of notes passing through the 

 press. 



In the year 1819, Mr. Bryan Donkin invented a counting machine, which 

 is described in vol. 37 of the Transactions of the Society of .Vrts ; it is called 

 " a machine applicable wherever it may be desirable to keep an account of 

 the number of revolutions or strokes, which may be made by the wheels or 

 levers of any other machine, in a given time or space ; as for instance, the 

 number of revolutions made by a mill wheel, or of the strokes of a steam- 

 engine beam in a given time, or the number of revolutions made by the 

 wheel of a carriage or perambulator on passing over a certain space." This 

 machine, like all the others used for a similar purpose, depended upon the 

 relative motion of a series of ratchet wheels with projecting rims, having 



