1842.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



197 



to incur a positive known exi«nse, which will not entail future liability, 

 than by Jiminishing the expense in the first instance to run the risk of 

 undergoing future loss. Thus, for example, if a line of railway upon a slight 

 embankment should cross a road on the surface of a wet or marshy country, 

 it will be better to raise the ruad to a sufficient elevation to pass it over the 

 railway, though the height of the bridge and approaches be thereby greatly 

 increased, than by slightly lowering and passing it under the railway at a 

 greatly reduced expense, to render it liable to be continually laid under 

 water. And these are the kind of circumstances that require so much care 

 and consideration on the p.art of the engineer, to enable him to judge of the 

 comparative amount of cost and maintenance "f the different systems which 

 he can adopt, and to regulate his designs accordingly. Now we might go 

 on thus increasing railway gradients until they approached nearer and nearer 

 to those of a turnpike road, were it not for the difficulty of regulating the 

 descent of them with safety. On a turnpike-road, writers have suggested 

 that from 1 in 36 to 1 in 40 is the best slope, because horses may gallop 

 down without danger, and, at the same time, it is a good trotting road up- 

 wards. But on railways it is not sate to go down such inclinations as that. 

 Professor Barlow lays down that when the inclination is greater than 1 in 

 160 all advantage from gravity in the descent is lost, from the necessity of 

 applying the break, and he has formed tables to show the amount of loss 

 sustained in the ascent ; thus, he states, that going up one mile of I in 100 

 is equivalent (of course with a maximum load) to going 2J miles upon a level ; 

 but he will not allow that any corresponding advantage is gained in the 

 descent of tins, or any plane steeper than about 1 in 180. Now, if this be 

 the case, we must have a totally different set of elements in forming lines of 

 railway from what 1 have been laying down. But, as has been already 

 stated, this is not the case in practice, for trains can have, with perfect 

 safety, the full benefit of gravity on all descents up to I in 100, and the 

 engines seldom carry maximum loads. The same line of argument has been 

 pursued with respect to turnpike-roads, where, however, there are many cir- 

 cumstanc s in operation which do not occur on railways — such as the un- 

 steadiness of horses and coachmen, which influence the question ; but the 

 great point to be considered is whether it is most economical to lay out rail- 

 ways with respect to stationary or to locomotive power. On this subject M. 

 Navier very sensibly remarks, that great rapidity being the characteristic of 

 railways, it has been considered necessary to employ locomotive engines, 

 which system presents an important advantage in being able to increase 

 gradually the number of engines as the demands of commerce require it. 

 whereas, on the stationary system, it is necessary to provide at once for the 

 greatest amount of traffic that can ever occur. But in the event of this 

 increase, we have still the means of using light and frequent trains for trans- 

 porting a heavy traffic over a line of inferior gradients, and reducing the 

 charge of the interest of that capital to the public. But whatever be the 

 description of country which the engineer may meet with, he should first of 

 all make or procure detailed plans on the largest scale, and upon them lay 

 down a number of surface levels, and from them, as from a model, to find the 

 line of least expense and greatest accommodation. The magnificent Ordnance 

 Maps of Ireland, from their great scale and numerous surface levels, will 

 render the task of the engineer in that respect easy, should the long-deferred 

 introduction of railways into that country be ever carried. 



LECTURE V. — ON THE COMPARATIVE ADVANTAGES OF DIFFEBBNT RAILWAYS. 



The class will, no doubt, be inclined to think that I have dwelt too long 

 in the first four lectures of the present course, upon the principles of economy 

 in motive power, but I assure you, that if, in after years, any of you follow 

 up the profession, you will find the subject one of the most vital importance. 

 I shall this evening draw your attention to the different elements of compari- 

 son which should guide the engineer in forming a selection from different 

 proposed lines of railway, and shall take, as a text-book for that purpose, Mr. 

 M'Neil,s translation of M. Navier 's work On the Afeans of Comparing the 

 Respective Advantages of Different Lines of Railway — a work which I highly 

 recommend for your private study, on account of the clearness and accuracy 

 of the views it contains. M. Navier states " that the elements of compa- 

 rison of different lines of railway may be divided into two heads ; first, the 

 establishment of a very rapid mode of transport — a consideration which should 

 give a preference to the shortest lines, the velocity being supposed to be the 

 same in all ; second, the increase of wealth which may result from the esta- 

 blishment of a line of railway. The construction of a railway, like that ofa 

 common road or a canal, is favourable to the advancement of wealth ; in the 

 first place, because the actual expense of transport in this direction is dimi- 

 nished ; and, in the second place, because this diminution in the cost of 

 transport increases the value of the neighbouring properties, facilitates the 

 establishment of new works, and increases production ;" and the saving 

 effected is not merely a private advantage to those individuals who may be 

 directly benefitted by it, but is so much actual increase of the wealth of the 

 country at large. " The first of these effects— that is to say, the diminution 

 obtained on the actual cost of transport— is the cause of the second, so that 



this diminution is the principal circumstance, and that which should be prin- 

 cipally considered." Taking it as established, therefore, that diminution 

 in the cost of transport is the principal thing, we come to the result that the 

 cost of motive power, on which this is dependent, is the leading point to be 

 attended to in the formation of any line of railway. Indeed, M. Navier goes 

 so far as to say that this is almost the only circumstance to be attended to ; 

 in his own words, " we should even say that the rate of reduction which is 

 obtained upon the actual cost of transport, by the establishment of a new 

 communication, is almost the only circumstance which should be thought 

 of ; " but he goes on to say, very justly, " it is also necessary to consider the 

 quantity of goods which is c.iiTied, or which may be carried hereafter, in this 

 direction," for the very essence of the railway system is to increase its own 

 traffic ! " for it is evident that it may be less advantageous to the countr> to 

 produce a great economy in the cost of transport upon a line where there is 

 but little to carry, and more advantageous to produce a less economy upon a 

 line where a large quantity of merchandise is carried." These are the prin- 

 ciples which I have been endeavouring to impress upon your minds, and which, 

 from their importance, I cannot too often repeat. '• It is, therefore," says 

 M. Navier, " generally necessary to take into consideration, in the compa- 

 rison of different lines, the quantity of traffic which may be established on 

 each, and even the increase in the value of properties, and the development of 

 production to which the establishment of these lines may give rise respec- 

 tively, according to the nature of the countries which they traverse, ' I 

 would observe, as a passing remark, that the word developpemenl, in French, 

 generally refers to length ; thus the development of a line of railway will be 

 spoken of— meaning the length of that line — whilst, in English, the word 

 refers to an extension of superficies. M. Navier does not go minutely into the 

 examination of these last elements of the question, which rather belong to 

 statistics and political economy than to engineering, but confines himself to 

 the " consideration of the reduction which the establishment of a railway 

 can effect upon the actual cost of transport — a most important consideration 

 — to which, as already remarked, It is alwajs necessary to attend ; and this 

 will form, in every case, the principal element of the comparison between 

 different lines, and often leads to determinations purely geometrical or me- 

 chanical, and, consequently, exempt from arbitrary deductions." 



M. Navier then goes on to state, that " the cost of transport on a railway 

 as upon a road or canal, depends on two principal points, which it is necessary 

 to distinguish and consider separately ; the first of these is the expense of 

 constructing the railway, and the second is the expense of conveying the 

 goods on the railway, when it is constructed. The e.tpense of the construc- 

 tion of the railway is independent of the quantity of merchandise and of 

 passengers that will pass over it. The expense of trausport, properly speak- 

 ing, upon the railway supposed to be constructed, depends, on the contrary, 

 upon the quantity of merchandise or of passengers — that is to say, all other 

 things being equal, the expense will evidently he in proportion to the ton- 

 nage." Now, a few years back, the whole time of the House of Commons 

 was taken up with comparing the merits of rival lines of railway, for no 

 sooner was one line proposed than directly a rival line was started. It is 

 well known that, for the Brighton Railway, four different lines were pro- 

 posed — the discussion on the respective merits of which extended over a 

 considerable length of time. But it is a curious fact, that, in all these dis- 

 cussions, the principle which has been laid down this evening was never 

 once alluded to. Now, in the practical working of railways, the diminution 

 of e.xiiense of transport is generally quite independent of the quantity of 

 goods carried, for, after a line is constructed, the charges are generally 

 airanged with reference to rival lines, or to the competition which may exist 

 with the railway ; and the interest of the money laid out is scarcely thought 

 of, however much it may have entered into the a priori calculations. The 

 Paris and Versailles Railways may be mentioned ; two lines were started, 

 one on each side of the river— the Government did not like to treat either 

 party harshly, and passed both bills, and both lines are actually executed ; 

 and, from the great competition between them, the charges for transport of 

 goods and passengers will probably bear little or no relation to the interest of 

 the capital expended. There is, however, another element which renders the 

 calculation of a very complicated nature. The railways are different from 

 common roads or canals, over which, after they have been once constructed, 

 the public have been left to find their own way— considerations of public 

 safety render it necessary to incur great expenses in terminal and local sta- 

 tions, &c. ! and there are also secondary expenses, such as the annual cost 

 of repairs, police, and management, of which it may be said that they depend 

 partly on the interest of the cost of constructing, and partly on the amount 

 of tonnage carried. Now, from experience a general idea can be formed of 

 the expense of these items, but, before gomg into the details, I will return 

 to M. Navier, who says—" We may, therefore, admit, without falling into 

 any serious error, that the annual cost of transport on a railway is, in all 

 cases, formed of two parts— the one proportional to the expenses of the con- 

 struction of the way, and the other proportional to the amount of tonnage 

 carried ; and we should also observe, that the cost of transport of one ton of 

 merchandise cannot be specified, unless the number of tons which shall be 



