4-2 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



of the plane, and making no deduction for friction, when it reaches 

 the bottom of the iilane, its velocity would be the same as that 

 attained by the falling body; now a body falls freely through 'JO 

 feet in two seconds and a half, at the end of two seconds and a half 

 il will have acquired a velocity of 80 feet ; but this velocity along 

 the inclined plane will have been acquired when the body has 

 reached the foot of the plane ; but in practice the resistance from 

 friction will be such as to reduce the velocity uniformly to a point 

 .somewhere about the mean, or lialf, which is proved by the experi- 

 ment, and the addition of weight can produce no efl'eet further than 

 to increase the momentum of the body by so much as the wciglit is 

 increased, but the velocity itself will be scarcely affected by the 

 change, for the same reason as a cannon shot or a bullet, if let fall 

 from the top of the Monument at the same moment, will both reach 

 the ground at the same time ; that this view of the case is correct, is 

 proved by the experiment down the Madeley plane, on the Grand 

 Junction Railway ; here, as in the former case, the carriages being 

 propelled down the inclined plane at a velocity of 30 miles per hour, 

 (it is only a fair experiment to jjrcsume the starling velocity in both 

 cases the same) and the carriages attained an u:iiform velocity of 30 

 feet per second, or 21 miles per hour, so that they were retarded 

 until they were brought to the velocity the inclination itself was 

 capable of generating without friction. 



Mr. Wood says, " The force exerted by 15C Ions down an inclina- 

 tion of 1 in 9() is equivalent to 3()-l lbs., and as this was the weight 

 of the train in the first experiments, it follows that such a coach 

 train, moving at 31 miles an hour, suffers a resistance of that amount, 

 which includes both friction and atmospheric resistance," or, what 

 is the same thing, tliat 364 lbs. represents the tractive force neces- 

 sary to propel such a train, at the rate of 31 miles an hour, upon a 

 level, including both friction and atmospheric resistance ;" 364 lbs. 

 raised 45 ft. per second is equal to tlie power of a 30-horse engine, 

 and to produce the same I'csnlts on a level, as shown by the experi- 

 ments, requires a locomotive, evaporating li)/'/ cubic feet of water 

 per hour, or, in other words, an engine of U)"'/ horse-power. This 

 fact proves, that the power of a locomotive to produce a high speed is 

 destroyed, or is most disadvantageously applied, and shows most 

 conclusively that the great loss of power is nottobeaccoimtcd for by 

 the atmospheric resistance, as proposed. 



As regards the observations respecting deflection, no notice seems 

 to have been taken of the comparative bearing surfaces of the stone 

 blocks, sleepers, iS;c. A stone sleeper is usually 4 ft. surface ; placed 

 at 3 ft. asunder will be 8 ft. bearing surface for the two rails, or a 

 yard in length. A transverse wooden sleeper is scarcely ever more 

 than 10 inches wide; if 6 ft. long, and 3 ft. asunder, the bearing sur- 

 face will be only .5 feet. A longitudinal timber is seldom wider than 

 13 inches, giving Gj ft. surface; this view of the ease at once ac- 

 counts for the superior solidity of the stone sleepers, for in fact the 

 question of solidity must always be brought down to a question of 

 surface, and that railway will be the most solid, other things being 

 equal, the rails of which have the widest base ; the mode, as admilted 

 by Mr. Wood, of fixing llie rails to the timbers is beyond all com- 

 parison safer than fixing thcni in chairs. A chair is seldom wider 

 than 4 inches, and an inch and a quarter thick at the point of lea.^l 

 section : then supposing them placed 3 ft. asunder. I '-, inch wdl be 

 distributed over a space of .3 ft., or a section of little more than one- 

 eighth thick of cast iron, is placed to bear all the concussion of the 

 engines and train, whereas, as in the case of Mr. Brunei's rail, everv 

 section of it is held down by a section of half an inch thick of wrought 

 iron, and the leverage of the rail reduced fully one-half less than 

 upon the London and Birmingham Railway. 



However additional smoothness of motion may be attained by the 

 removal of the piles and transoms, unless additional bearing sur- 

 face be supplied, or the line perpetually packed, the levels will be 

 lost by the sinking .of the timber, for it is quite absurd to expect that 

 any degree of consolidation can take place in a yielding and inelastic 

 soil. In my opinion, the only proper method to be adopted is, to 

 place the cross transoms closer together, and foi'in a sort of flooring 

 under the longitudinal timbers, thus throwing the load upon a wider 

 surface, and tliis would be equally desirable if the weight and stiff- 

 ness of the rail is increased. 



Mr. Wood, in his enumeration of the conditions to be taken into 

 accountto form a perfect carriage, has omitted to note the perfect 

 parallelism of the axles, a condition of more importance than any 

 other, for if this be correct, the carriage is certain to run well. 



The machine described to have been used to note the various vibra- 

 tions, in my judgment nmst have been very ill adapted for the pur- 

 pose ; it must have been too mercurial, too sensible ; had a heavy 

 pendulum been employed instead, it would have given far more 

 batihfaetory results. 



There is no doiil^t thai the proper mode to liuk carriages, 50 that 



there shall be no concussion, is by an inflexible link between each 

 carriage. Mr. Booth's patent draw-screws produces a good effect, 

 but the simple inflexible link as adopted by Mr. W. J. Cm-tis, on the 

 (ireenwieh Railway, is much more simple and very much better. 



The 7 feet guage, which has been so nuich reviled, is most un- 

 questionably the only gauge to carry out the plan which has been 

 recommended by every person who has studied safety in railway 

 travelling, and by no one more so than Mr. Brunei himself, to place 

 tlic carriage within the wheels. By tloing this, and allowing only one 

 inch clearance, a width of 6 ft. 6 in. is obtained, and lowering the 

 carriage to within 6 inches of the rail, a vertical height of / feet is 

 procured, giving an area 45 ft. G in. ; so that the Great Western car- 

 riages will be to the London and Birmingham as 45 ft. 6 in. to 53 ft. 

 and it is impossible, with the London and Birmingham carriages, to 

 make a similar improvement, without making them 8 or 12 inches 

 wider. 



One great advantage results to the public from the investigation 

 ^\hieh has taken place into the merits of this railway, proving the 

 very defective condition of the system of railways generally, ren- 

 dering it the imperative duly of railway companies to avail them- 

 selves of the suggestions and improvements of others, besides their 

 own people. If it has the effecl, thei'efore, of breaking down the 

 spirit of domination and exelusiveness at present existing, which 

 forbids the introduction of other methods than the crude and original 

 ideas of Stephenson and Co., such a conclusion is well obtained at 

 the expense and noise this in(iuiry has created, and must be regarded 

 with satisfaction by every well-wisher to the railway system, and by 

 none more so than by 



AN OLD ENGINEER. 



LETTER FROM WM. TURNBULL, Major U.S. Topographical 

 Engineers. 

 It is with considerable pleasure that we publish the following 

 letter received from a highly respectable and valuable member of the 

 profession residing in the United States. We are happy in enlisting 

 him as a correspondent to the pages of our Journal, and it will be a 

 gratification to ns to receive the oilier engravings of the Potomac 

 Aqueduct promised by the Major, in order that v-e may be able to 

 lay before our readers the progress of that \\ork. 



Washington City, Aug. 31, 1838. 

 Sir, — Several months ago, when a specimen number of your 

 valuable journal was exhibited in this eily, I became a sub- 

 scriber ; but, owing to the remissness of our booksellers, or the 

 want of a proper agent here, I did not receive it until within a few 

 days, when I received three cpiarterly numbers at once. 



I feel highly flattered that you should have thought a description 

 of the work (Potomac Aqueduct) imder my charge, worthy of a 

 ]ilaee in your joinnal, and avail myself of the opportunity of our 

 Charge d'Aflaires to Belgium, M. Virgil Maxey, who visits London 

 on his return to Brussels, to send you a copy of the drawings and 

 description, which have been added to since the first publication. 



There are still three or four more drawings, showing the condition 

 of the work at the end of the year 1837, and some changes, sug- 

 gested by our experience, made in the construction of the coffer- 

 dams, which have proved of great utility, and which should accom- 

 pany the description, but, unfortunately, they are yet in the hands of 

 the engraver. I shall have the pleasure to forward them by the next 

 opportunity that offers. 



The subject of coffer-dams is one of peculiar interest to me. I 

 remarked in the third number of your journal, a drawing and descrip- 

 tion of the eoftcr-dam to be used in the constniction of the terrace- 

 wall, &c. of the new Parliament-house, and hope that it will be in 

 your power to give some details of the operations of emptying, &c., 

 as that work progresses. 



On examining the plan, I observe a great many iron bolts, passing 

 through the puddling at different heights. I was once forced, by 

 the spreading of the outer row of piles,"to use bolts in a similar way, 

 at low-water mark ; and, as the puddling settled, a cavity was left 

 ruider each bolt, through which the water found its way, and was the 

 cause of very great inconvenience : the dam was filled with water 

 several times by means of them. 



I should be much pleased to know their efl'eet in the coffer-dam for 

 the new Parliament-house. 



With my best wishes for the success of your journal, which, I 

 think, bids fair to be of extensive utility. 



I have the honour to be, Sir, very respectfully, your obedient scr\anlj 

 WILLIAM TURNBULL, 



Major U. S. Topo. ilngiueers. 



