1842.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



383 



way of calculating the annual cost on lines of little intercourse, on which, 

 however small the traffic might turn out to be, yet a certain number of en- 

 gines must be kept to do any worlv at all. The commissioners, in following 

 out this inquiry, endeavoured to determine the proportion the cost of loco- 

 motive power bore to the total working cost of a railway. For the Liverpool 

 and Manchester line it was found that this proportion was only one-fourth 

 the gross annual charges on that line, including much town carriage of 

 goods collected and delivered ; but on the Dublin and Kingstown Railway 

 the proportion was, at that time, nearly one-half. It was observed Ly the 

 Professor, in a digression, that for the average of railways it was now deter- 

 mined to be about one-third. The commissioners finally assumed the cost of 

 locomotive power to be one-third of the total expense of working a line of 

 mixed traflic, and that to run a given number of trains per day, a certain 

 number of engines must be provided ; it was then calculated that £1750 

 a year would be the cost of each engine to work about from 25,000 to 30.000 

 miles annually, and then they computed the amount of gross receipts neces- 

 sary to cover those expenses and interest of capital. This was working back- 

 wards, to ascertain whether it is justifiable to make a railway at all in cer- 

 tain districts. The result of the commissioners' calculations were, that, sup- 

 posing there went only two trains daily throughout a given line, the average 

 load of each train ought to consist of either fifty tons of goods or eighty 

 passengers, or a mixed load of twenty-five tons of goods and forty passengers, 

 or in that proportion, in order to justify a line being made — the average 

 charge for passengers being assumed each IJrf. or for goods 2d. per ton per 

 mile, which, it may be observed, is scarcely th: half of the average rates of 

 charge on the principal English railways. Mr. Vignoles observed, in con- 

 clusion, that having shown that the cost of conveyance of passengers, mer- 

 chandise, minerals, &c., could be nicely calculated from the experience 

 gained, and could be brought to the definite mileage rates before mentioned, 

 he thought the proper raiiway charge should be, double the cost for working; 

 which, when the railways had been judiciously constructed, and without 

 extravagance, would sufficiently remunerate the undertakers, as such mode- 

 rate principle of charging would bring the most traffic. 



PROCEEDINGS OF SCIENTIFIC SOCIETIES. 



INSTITUTION OF CIVIL ENGINEERS. 



May 31. — The President in the Chair. 



On the cons/ruction of Model Maps, as a better mode than Sectioplam- 

 graphy for delineating the Drainage and Agricultural Improvements of a 

 Country, or projected lines of Railways, Canals, Sfc." By John Bailey 

 Denton, Assoc. lost. 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 ena- 

 bled 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 pecuharly 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. The 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 expense of making a model ot an estate 

 of compact form is stated to be from 2s. 6d. to 3s. 6d. per acre. 



" Observations on the Periodical Drainage and Replenishment of the Sub- 

 terraneous Reservoir in the Chalk Basin of London." By the Rev James 

 Clutterbuck. 



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. \V. 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 helow, it accumulates until it finds vent by several deep 

 Yalleys which incline southward, and carry off a large quantity of water by 

 the streams Ver, Gade, Belbourne, 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 on the water level, regulated by these vents, 

 dipping towards the south at an average inclination of nearly 300 feet ia 

 fourteen miles, may be represented by a line drawn from the upper district 

 at an angle, and terminating at the river Colne. 



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. A 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 repre- 

 sented 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 dis- 

 trict during the replenishment of the reservoir, which usually occurs be- 

 tween December and March inclusive, the water accumulates in a proportion 

 increasing with the distance from the river or vent, and falls off in a cor- 

 responding 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 

 Une 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 ex- 

 treme 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 consider- 

 able 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 con- 

 tinued 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 difl5cult to ascertain the extent of the 

 natural alternations of that part of the water level which underiies the 

 London and plastic clays ; the difficulty is increased by an unnatural depres- 

 sion caused by the exhaustion of water under London, which is said to in- 

 crease 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 wUl 

 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 re- 

 duction will be found, faUing 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 mea- 

 surements 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 the 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 



3 II 2 



