1842.1 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



165 



of Titian — his battles of the Republic, painted in oil colours — were al' 

 destroyed in the burning of the Senate House. 



I have now enumerated many of the advantages which will result from the 

 introduction of fresco painting into England. I have considered, and, I trust, 

 to some extent proved, its claim, as the only style of painting adapted to our 

 architecture, from its light being suited to all times and places — its powers in 

 colour and effect being equal to the powers of water colour and oil painting 

 combined together — its durability, suited to the nature of our soil and climate, 

 and even our customs, including the accidents of fire ; and in conclusion I 

 will observe, that the cheapness with which it may he executed — certainly, 

 I should say, one-half the price of oil painting — will confirm and ensure all 

 these singular advantages. I have no doubt, therefore, we shall have English 

 painting extend from one end of the kingdom to the other, as a universal 

 language. In looking on the greatness of fresco, and its positive relation to 

 architecture, I would say that fresco painting is the true sister of architecture, 

 and oil painting only the sister-in-law. 



MR. VIGNOLES' LECTURES ON CIVIL ENGINEERING, AT THE 

 LONDON UNIVERSITY COLLEGE.* 



SECOND COPHSE — LECTURE I. — KAILWATS. 



Mr. Vignoles commenced by saying, that, in pursuance of the order slated 

 in his intreductory lecture, he would proceed to investigate the principles 

 upon which railways should be laid out under varying circumstances. In 

 calculating the power (of whatever description it may be) necessary to over- 

 come the resistance of a load to be moved on any railway or ro.'jd, it may be 

 dividedjinto two parts — viz. that necessary to overcome gravity, and that 

 required to meet friction. The former is. of course, common to, and equal 

 on, all descriptions of roads deviating from the horizontal line, and is in pro- 

 portion to the sine of the angle of inclination ; the latter is regulated by the 

 degree of perfection of the road, and of the vehicles moved upon it, and in- 

 cludes the resistance of all obstacles to the rolling surface, or periphery of thu- 

 wheel, in addition to the axle friction due to the load or weight placed upon 

 the carriage. It has been assumed, from experiments and observation, that 

 the average friction upon a railway is 9 lb. per ton, and that this continues 

 the same at all velocities ; but there is reason to believe that the latter part of 

 the assumption must be much qualified. The gravity due to the inclination 

 of the plane being added to, or subtracted from, the friction, as the plane 

 rises or falls, the sum, or difference, will give the total amount of power 

 necessai-y to overcome the resistance of the load. The power necessary to 

 overcome the gravity being expressed by the proportion which the rise of 

 the plane bears to the weight to be raised (say, for example, a ton), is found 

 by dividing 2240, the number of pounds in a ton, by the denominator of the 

 fraction which expresses the inclination of the plane ; thus, on a plane rising 

 one foot vertically in a horizontal distance of lOOOfeet, the fractional expres- 

 sion is Yiruo' ^^^ "'^ power (retarding or aiding the load), w ill be the thou- 

 sandth part of a ton, or 2i lb. It is evident that, as we arrive at steeper 

 inclinations, this power will at length become equal to that required to over- 

 come the friction ; thus, on an inclination of ^^, it will be 2^" = 9 lb. per 

 ton, and this being subtracted from the friction, on a railway which is com- 

 monly taken at that same amount of 9 lb. per ton, it results that no power 

 is required to move a load down such an inclination, or wherever the gravity 

 and friction are equal, and balance each other. The angle that such an in- 

 cHnation makes is called the angle of repose, but will, of course, vary with 

 the friction due to various descriptions of roads and vehicles. On steeper 

 inclines than such, not only is no power wanted, but there is a gravitating 

 power due to the descent of the plane, and so strongly does this act in steep 

 inclinations, that it is neces,sary to put on the break, to retard the velocity 

 which it occasions. It is found, however, when a train is allowed to descend 

 a steep plane without retardation, that, owing to the resistance of the air, it 

 will, after acquiring a certain velocity, cease to be further accelerated ; many 

 theoretical writers have fallen into error, by supposing it dangerous to allow 

 trains to descend inclinations steeper than the angle of repose without apply- 

 ing the break. On railways where there are inclined planes of -^, for 

 several miles together, the trains often commence the descent at the 'ra"te of 

 upwards of forty miles an hour, and the speed, instea 1 of being accelerated , 

 has been quickly reduced to little more than the thirty miles an hour, or to 

 such uniform velocity that a railway train will acquire on that inclination, 

 varying a little with the weight of carriages, or the length of the train ; such 

 being the case, it is evident that lines of railway for locomotive power, can 

 be safely laid ont with inclinations of 1 in 100, and even steeper. 



It is of the utmost importance, in laying out a line, to consider the power 

 which is proposed to be employed, and the mode of obtaining it ; thus, if it be 



• We are indebted for these reports to our cotemporary the " Mining 



intended to lay out a horse railway, to carry coal from a colliery to a shipping 

 place, the line should be made always to descend, and so regulated, that the 

 number of full wagons that may be sent down be that number which may 

 be taken back empty. But horse-power being extremely limited, recourse 

 is had to steam, and the locomotive steam-engine has been applied to railway 

 travelling, as being better suited to the purpose than animal power. The 

 power of the locomotive engine may be defined, not so much by horse power, 

 or cylinder power, as by boiler power, or capability of rapidly supplying steam 

 to the cylinders, and sti'l more by adhesive power, or the weight insistent on 

 the driving v heels, so as to have purchase, as it were, to drag the load after 

 it, for the wheels will slide, more or less, and, under some circumstances, 

 will merply turn round on the rails, without progressing. Many lines appear 

 to have been laid out under the impression that the locomotive engines would 

 always have to carry a ma.iimum load, and. in accordance with tliis principle 

 and to enable them to do so. it was some short time since laid down as an 

 axiom, that no inclinations should exceed ^^, and that gradients should be 

 constantly uniform through the whole lengih of a line. Experience has 

 shown, however, that the practical cost of conveyance of ordinary trains 

 over lines greatly varying in their gradients, does nut materially differ, the 

 wear, and tear, and fuel, seldom being increr.sed so much as 10 per cent., and 

 the other expences and ci ntingences being the same, whatever the gradient 

 of the railway, the difference on the whole expence of working and mainte- 

 nance becomes very small indeed. In laying out a line, then, the traflic most 

 be considered quite as much in the distribution of it as in the totality ; for it 

 is evident that, to accommodate the public, the trains ought to go often, and 

 will, therefore, generally be light; and when we consider the great economy 

 in construction, and the little additional expense incurred in the after work- 

 ing, we may conclude that railways may be advantageously laid out with 

 much steeper inclinations than they have in general hitherto been, particu- 

 larly in the remoter districts, where the railway system has not yet been 

 extended. A powerful engine will draw an immense load on a level, whereas 

 it often has not more than twenty tons to draw — consequently, gravity ceases 

 to become an object ; and even should the traflic increase in course of time, 

 it will be better to send frequent and light trains than, in the original con- 

 struction, to incur heavy cost to graduate the road for heavy trains, w hich 

 are seldom to be carried. This principle must, of course, be confined within 

 certain limits ; thus, lines may be laid out with better gradients, where the 

 traffic is very great, an<l will justify the expense and inconvenience which 

 might result from an engine having always to go up a steep ascent. Rail- 

 ways in England have cost, on the average, £30,000 per mile, and the first 

 cost of locomotive power does not amount to oue-fifteeenth of that sum. The 

 interest on the capital is, therefore, very great, while that on the power is 

 small, as is also, comparatively speaking, the daily cost of transit due to the 

 power only. If these proportions were different, the latter being increased, 

 while the larger amount (the interest on the cost of the works) were dimi- 

 nished, the capital sunk in railways might have been reduced fully one-half, 

 with equal satisfaction and benefit to the public, for whose use they were 

 designed, and with greater profit to the shareholders. 



LECl'CRE n. R.A.1LW.1IS — LOCOMOTIVE POWER. 



Ln the last lecture it had been stated that the adhesive power of the loco- 

 motive engine depended upon the weight borne upon the driving-w heels. Tlie 

 greatest amount of adhesion of iron upon iron, according to the experiments 

 of the eminent engineer, Mr. George Rennie, as published in the Philosophical 

 Transactions, appears to be about one-sixth or one-seventh of the weight of 

 the insistent load. In the locomotive engine, where the bearing of the wheels 

 is upon smooth surfaces, the adhesion will, of course, be less ; and in weather 

 when rime or mist congeals upon the rails, it is very small indeed, sometimes 

 none at all. But in ordinary states of the rails, and of the atmosphere, one- 

 fifteenth may be taken as an average. The vicissitudes to which this power 

 is subject, will often account for the varying rates of railway travelling, and 

 it is only when the resistance of the load is less than the smallest amount of 

 adhesive power which the state of the weather or the rails will admit, that 

 the time of transit of a train over any given distance can be insured. Now, 

 the usual weight bearing upon the driving-wheels of an ordinary locomotive, 

 for passenger traffir, is about seven tons, or 15.680 lb.; one-fifteenth of this 

 will be 1042 lb., or, in round numbers, say 1000 lb , for the average available 

 adhesive power of such an engine for moving a load, and on the amount of 

 this alone will depend the weight which the locomotive engine can draw after 

 it. The other principal element which must be taken into account in the 

 locomotive engine — viz. the speed — will depend mainly upon the power of the 

 boiler to generate steam with sufficient rapiility. A boiler may have quite 

 sufficient power to muve (at avelocity of three miles an hour) a load of which 

 1000 lb. shall be the representative, but it must be of a far superior descrip- 

 tion, and far higher powers, to move the same load at a velocity of thirty 

 miles an hour ; and this subject does not appear to have been sufl^iciently 

 considered, though it is of such paramount importance thoroughly to under- 

 stand the nature of the moving power to be used, before going into the 

 subject of the gradients, or the principles of laying out the line. The amount 



