314 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[OCTOBEK. 



sure me lliat tlie tlipory is correct." We here see a laudable djsire to 

 take every precaution to ensure success — tlie theory is studied, a model 

 is made, Vu''i o( the size of tiie bridge, yet somehow theory, commnon 

 sense, and experiment all fail, and the blame is laid on tl>e contractor; 

 In my opinion there was another weighty reason. The time of its 

 occurrence is singular enough. 



Mr. Dri'dge asserted that "the Menai chains weigh 1,935 tons," 

 and lie still affirms that on his plan only T.'yth of the weight of iron 

 would be required to construct a bridge of equal strength. I should 

 like to know by what means Mr. Dredge has arrived at this result. If 

 there be such virtue in the mere inclination of the suspending rods 

 and the variation of the thickness of the chain?, 1 am very naturally 

 surprised that such an eminently practical man as Telford never 

 thought of that modification. As Mr. Dredge does not understand the 

 dilTerence between underminirg an erroneous theory and accomplish- 

 ing an impossibility, 1 do not see the force of his "ergo." 



Mr. Dredge might as well have told us at once, that a weight of one 

 pound, placed on a table, would produce a pressure of two pounds, 

 half of it acting in each direction, for action and re-action are equal 

 and opposite. In the "Penny CyclopEedia" is a simple and correct 

 illustration of the meaning of tension; "when a weight is supported 

 by a siring, the tension of the string is the weiglit suspended by it." 



It will be unnecessary for me to write any more on this subject 

 unless Mr. Dredge abandons his authorised theory altogether, or re- 

 moves my objections. I also feel it to be equally vain and useless to 

 attempt to argue with one who countenances such absurdities, shews 

 his ignorance cf one of the commonest of terms, and lays claim to be 

 considered a mathematician. 



It is, however, desirable for Mr. Dredge to state distinctly what is 

 given and what is to be found by theory, and also what theory it was 

 that the Indian engineer studied. 



I hope enougli has been said, backed by the subsequent failure of 

 theory and practice in India, to induce those in authority to insist on 

 a satisfactory mathematical theory being given, and approved of by 

 a competent judge. If the plan be good, there will be no need to fear 

 the ordeal, and if not, it is for the good of all to abstain from using it. 



ATMOSPHERIC RAILWAYS. 



ABSTRACT OF THE EVIDENCE BEFORE THE COMMITTEE OF THE HOUSE 

 COMMONS. 



CContinued from page 28i.J 



[We again earnestly invite our readers* attention to tile analysis of tliis invaiuabie mass 

 of evidence of wliictl ive have caretuliy endeavoured to give a complete abstract; we are 

 well salislied tliat it will repay the tiouble of perusal,] 



Level Crossings. — Explanation of witness's contrivance for allowing roads 

 to cross an atmospheric railway upon a level ; its self-acting principle de- 

 scribed — (Samtida.) 



" A cover is placed over the tube, which cover is raised by the vacuum 

 formed in the tube, working on the lower side of a piston ; the cylinder de- 

 scends by the removal of the pressure from below it, and in descending raises 

 the cover, which had been previously lying flat on the pipe, and that forms 

 a barrier to prevent carts passing till after the train has passed ; when the 

 train has passed, that tube Ijeiiig refilled with air at the atmospheric density, 

 equalizes the pressure on both sides of the piston, and the cover, by its own 

 weight falls. — When the cover is raised it forms a barrier, so that carts can- 

 not come upon tlie railway at the time the train is passing ; and at the same 

 time it gives an intimation that the train is approaching, though it is out of 

 sight. There would be no difficulty in connecting this cover with an actual 

 barrier outside the line. Mr. Brunei's idea, upon seeing this, was to modify 

 it to that extent to make the cover, instead of dipping partially only over the 

 tube, a continuous barrier over the entire width of the road. — Supposing 

 there were a cart passing, it might so happen that you might catch the cart 

 between the two wheels ? That would scarcely happen, because the heavy 

 number.s of the vacuum are formed very slowly, and the cart would have 

 plenty of time to pass over during that time. There would he no difficulty 

 n making the barrier the height of a horse. And those barriers might be in 

 the form of an ordinary gate." 



Lines of Rails : — 1. Generally. — 2. Sufficiency of a single Line of Rails on 

 the Atmospheric Plan. — 3. Impossibility of working an Atmospheric Line 

 iirilh a single Tube. — 4. Opinion that a single Line is as applicable to the Lo- 

 comotive System as to the Atmospheric. 



1. Reasons for witness taking provision, in the schemes in which he is en- 

 gaged as engineer, for laying down a double line of rads — (Vignoles.) 



" Have you any otjection to state v,\\y you have taken proxisions in those 

 schemes in which you are now engaged as engineer for laying down a double 

 line of rails, anticipating, as you have staled you do, that the atmospheric 

 system will he applied to some of those lines ? — I have not the least ohjec- 

 lion to state the reason. The reason is, that a great number of the directors 

 and persons connected with those railways have not that confidence in the 



atmospheric system which I have ; in fact, I may say that I am somewhat in 

 advance of the companies and the public generally upon that point. 



" The line I have more particularly in view is the line between Blackburn 

 and Bolton. The traffic upon that line is very great indeed, and it has to 

 pass over a summit of nearly 600 feet in the course of seven miles. The 

 gradients I have laid down are 1 in 70, and I can get nothing better; and 

 even with those gradients of 1 in 70, I have an enormous tunnel, and several 

 viaducts of very great height: but still the traffic is such as to justify the 

 construction of a line, and the Board of Trade have approved of the' fine. 

 The question has not been raised how that line is to be worked, but I have 

 no doubt that when the atmospheric system comes to he tried and proved, 

 (and it requires, in order to convince the public mind, to be tried somewhere 

 on a sufficiently large scale), the directors of that company will he prepared 

 to listen to my suggestion for a single atmospheric line, instead of a double 

 locomotive line. If the directors of that company had, in the first instance, 

 adopted a single atmospheric line, a considerable expense might have been 

 saved. The length of the line is 13 miles; and I am quite certain that in 

 that distance I might have saved 50,000/. in earthworks, and so forth. You 

 would not have considered it necessary to have a gradient of 1 in 70, if the 

 atmospheric system had been adopteil ? — No, I should have sut)stituted gra- 

 dients of 1 in 40, and 1 in 50 ; but, at the same time, the peculiar character 

 of the country is such, that the deep chasms on the side of the mountain 

 cannot be overcome, even with a gradient of 1 in 40, or 1 in 50. But you 

 could not have overcome the difficuUies of the country, even with a gradient 

 of 1 in 40 ? — No. If 1 had had a tunnel for a single line only, of course it 

 would have been much cheaper ; the great saving viould have been in lower- 

 ing the viailuct, and shortening the tunnel, and in the general character of 

 the earthworks being somewhat smaller; and 1 consider that about 50,000/. 

 would have been saved in earthworks. Is the expense of earthworks en- 

 hanced by the difficulty of making an embankment at the summit sufficiently 

 strong to carry two lines of rails ? — No, it is increased, but not in proportion 

 to the height. I must also mention that there is another point peculiar to 

 this line. The countiy through which we pass is full of manufactories with 

 ravines of water. Wherever we cross those ravines we have an opportunity 

 of making dams to hold up the water ; it is in working a line like this that 

 economy would be obtained, from the great traffic that there would be upon 

 it ; working by the atmospheric system over these gradients would be a great 

 deal cheaper than working by locomotive engines. — You would be able to 

 keep the stationary engines in constant work ? — Yes ; or we might keep a 

 smaller description of engines, and work our air-pumps by means of reser- 

 voirs." 



2. At present the atmospheric principle might not answer so well with a 

 single line upon a great trunk railway ; more experience is needed before that 

 is tried— (KeW.) 



The single line of the South Devon Railway will be sufficient for its traffic, 

 even if it shoidd be as great as that of the London and Birmingham. — 

 On the inclined planes on the South Devon line there will be double lines of 

 rails, as the descending trains may run down without a tube; this will give 

 great facilities for meeting trains to pass each other — {Brunei.) 



Manner in which witness could carry out his suggestion for a single atmo- 

 spheric line between London and Portsmouth ; it would be perfectly ade- 

 quate for all the traffic of that district — (Ciibitt.) 



" Between London and Portsmouth there is to be a single line if they ob- 

 tain their Act. I think it will be adequate for all the business of that dis- 

 trict. The means of carrying it out are by having what I call a double sta- 

 tion, at intervals of six or eight miles, or whatever upon experience may be 

 deemed most convenient, but about that distance, where the trains could 

 meet and take in passengers, and hook on wagons and goods, and transact 

 their business there in a few minutes, and then proceed on again ; then the 

 whole would work regularly, the stoppages there taking place at the same 

 time, and the trains starting at the same time." 



3. Upon the most mature consideration witness is perfectly satisfied that 

 working a line with a single pipe is physically impossible; reasons for enter- 

 taining this opinion — {Stephenson.) 



" As an abstract question, supposing the electric telegraph to be applied 

 to, say, the London and Birmingham line throughout, 1 can see no more rea- 

 son, looking at the regularity of the trains and the comparative certainty of 

 operation with the locomotive engines, why 1 should not, upon a piece of 

 paper, devise a plan and system of operations by which trains might move 

 with locomotive engines, on a single line of railway, with an electric telegraph, 

 between here and 13irmingham, as easily as upon a line constructed upon the 

 atmospheric system ; I can see no ditference. But in the case of a traffic 

 like that, sometimes the trains passing from Euston-square within a quarter 

 of an hour of each other, and the average times of the trains being about an 

 hour after each other, 1 should never recommend the use of a single line, nor 

 should I think it feasible or practicable to work traffic like the London and 

 Birmingham traffic upon a single line. Ever since the question was broached 

 about working a line with a single pipe, I have maturely considered it, and 

 most anxiously, with a view of coming to a correct conclusion upon it ; and 

 I am perfectly satisfied, after 20 years' experience, working a lailway daily, 

 that the thing is physically impossible. Will you state your reasons for en- 

 tertaining that opinion .'—The nnndier of intersections would lie so great, 

 and the irregularities arising upon lines are numerous. The application of 

 the atmospheric system implies the utmost conceivable regularity in the ve- 

 locity from end to end of the line, in order that the meetings of the trains 



