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Traction on rail-ways
Traction on R a i L w a y s .
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,Oatl ./tttrltlon Compound. T o one part of lime water (a saturated solution of lime) add one part of olive oil, unite them well by thorough slitring or agitation, and they form a soapy compound of the consistence of cream. If too weak for the purpose, more oil may be added. This compound is said to be better than pure oil for the lubrication of small works. For cogs or teeth of wheels, whale or common oil may be taken in the proportion of one part to two of lime water. It assumes the consistence of thick paste, when a small quantity of carbonaceous matter, such as plumbago, or soot, may be added and well incorporated. For this compound a patent was taken out in England, by ~ . Partridge, in December, 1835. Lo~. Jour. Arts ~ndSciences. Lubricalion by Water. S i r , ~ I perceive in the report, of the Times, of the proceedings of the scientific meeting at Bristol, that Dr. Lardner suggests placing water-pots before the wheels of a train of railway carriages to reduce the friction. T h e fact of a train running lighter on a wet (lay is well known to every engine driver; and it occurred to me to avail myself of the water leaking from the boiler, or tender~ passing it, in the first instance, into the ash-pan, from which the excess drops in a small jet behind the engine wheels; thus the engine passes over the dry, and the tender and train over the wetted part of the rail. In the event of the boiler being so tight that the leakage would be insufficient, two small tubes, with regulat~ ing cocks, should pass from the tender~ or cistern, and discharge a small j e t on the rails as the train passes along. I shall feel obliged by your insertion of this letter in your earliest Number, in order to advance my title to the priority of this useful adaptation of what would be otherwise lost water. YouFs~ ~c. W . J . CURTIS. Lon.Mee,~{ag.
Progress o f Civil E n g i n e e r i n g . Traction on l~ail-wass. From an article in the Dublin Review, No. 1, (May, 1836) on "The Rail Road S~stem
in Ireland."
A modern R a i l w a y m a y be defined to be a perfect R o a d - - h a r d , dry, and level, presentin~ the least possible resistance from irregularities of surface or inclination. Vehicles p r o p e r l y contrived, and furnished with wheels and axles, peculiarly constructed to move along the iron t r a c k s with the least friction; and the untiring mechanical engine~ compressed into the smallest useful compass~ mounted on a carriag% supplied from a portable boiler~ with steam at a high pressur% and yoked in front of the frame to be moved~ give forth an irresistible power, t r a n s p o r t i n g passengers and merchandize with a speed and economy wholly unattainable by means of animal resources. T h e force necessary to move any given load on a horizontal line, is expressed by writers on mechanics in terms of the load itself. On a, Railway extremely well laid, and in good order~ with the bearing per i m e t e r of the wheels turned perfectly true; with the best fitted axles~ properly lubricated~ and the iron rails clean and dry, or quite wet, the friction is reduced to its lowest terms. By friction is to be understood the sum of the obstruction to the movement of the c a r r i a g e or train of
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_Progress of Civil Engineering.
carriages, arising from the resistance to the rolling p e r i p h e r y of the wheels as they move along the rails~ and tl~e friction at the axles from the insistent load. T h e amount of resistance is small~ and, supposing the rails Io be clean and in order~ need not~ by the general enquirer, be distinguished fi.om the sum total of the friction. E x p e r i m e n t has satisfactorily proved, that the friction is the same at all velocities. To overcome this frictions or~ in other words~ to overcome the vis inertix of the load, a certain power is requisit% varying somewhat, as will be presently shewn; but which power, on a Railway, is now usually taken to be about ~ 01 t h part of the load, whatever that may be, Now a ton consisting of 2240 lbs. the 5~gth p a r t thereof is 9 lbs. nearly; and it is the ordinary expression in Railway parlance~ to call the triction 9 lbs. to the ton. Some engineers prefer taking 10 tbs. to ~he ton, or ~ s t h part of the loads as the measure of the friction~ in all states of the weather, of the Railway and of the carriages. Otherscon~ sider that 8 tbs. or 5~\6th~ or even 7~ Ibs~ or ~-~z)-thp a r t of the load, to be a sufficient allowance. The above tbrm the extremes for practical purposes; but experiments have been made on c a r r i a g e s , with axles so I~ frl"C tmn, " constructed, and the Railway in such go0d order~ that tlie in one case, appeared to be as small as 2} lbs. to the ton, or --a--th hart 10001 t" of the load; and in some other instances, only 4 or 5 lbs. or ~rv()~h of the load. T h e s e are, however, only interesting as illustrative of what is possibI% under very peculiar circumstances; but like many experiments on models, would lead to false conclusions, and be deceptive, it sta~ed to be true in general practice. U n d e r all the states of road and weather, then, the exertion of a force (animal or mechanical) of 9 or 10 lbs. will move a ton upon a level Railway. Now an ordinary hors% travelling at the rate of about ~ miles an hour, and working 10 hours daily, exerts a force of about 128 lbs. This~ indeed, is a point rather unsettled a m o n g engineers, and a horse-power is usually taken higher; but it is a safe average for all horses. T h e m o m e n t a r y effort of a powerful London d r a y horse is perhaps four or five times what is above assumed~ while a weak, ill-fed animal~ used t h r o u g h a long journey~ would be scarcely equal to half the above effect. A n ordinary horse can tak% however, about 14 tons along a level Railway, at the rate of ~ miles an hour~ working all (lay; but the power of an animal to draw is diminished as he is driven more rapidly. A horse capable of travelling 1~ miles per hour, would only draw 3 tons on a level Railway at that velocity, and could not continue to do so any length of time. T h e application of animal power is therefore very limited, and it is to steam recourse has been had, to obtain high velocities. T h o u g h it is t¢'ue that the friction s and of course the power, requisite to move the dead weight~ is the same at all velocitie% yet the velocity itself is only obtained in the ratio with which the power to o v e r c o m e the friction of the load is supplied. In a locomotive steam engine, of the best modern construction, the velocity may he defined in a general way, to he regulated by the b o i l e r - p o w e r ~ t h a t is, the capability of the boiler to supply steam~ of effectively high pressure, with sufficient rapiditys so as to enable the pistons to make a greater number of strokes per minute, thereby t u r n i n g the wheels round a greater number of times~ and of course u r g i n g the machine to a h i g h e r speed. So the load which the same engine can draw, supposing it to have sufficient adhesion on the rails,
TraeHon on Rail-ways.
47
may be expressed to be regulated by 'the d i a m e t e r of the cylinders, the pressure of the steam, and the length of the stroke of the piston, from which elements are obtained a certain expression of value in lbs. called the cylinder-power, which, divided by 8, 9, or 10 lbs. as the friction may he assumed, gives the number of tons which the engine is capable of drawing. T h i s is by no means a scientific, and perhaps not a strictly correct description; but it will convey an a p p r o x i m a t e idea of the power and effect of the locomotive engine, which is all that is necessary on the present occasion. The most r e m a r k a b l e circumstance in the application of steam-power on railways, is the mode in which the steam, having done its duty in the cylinders of the eng'ine, is discharged up the chimney, and entering therein under a pressure still considerably h i g h e r than the atmospheric pressure, produces a m o m e n t a r y vacuum; this is followed by a rush of air from the flues or tubes of the boiler, thus creating a great draught from the furnace, and, by d r a w i n g the heated air in the increased velocity t h r o u g h the tubes~ generates steam in the boiler with proportionate rapidity. T h i s steam supplies the force to overcome the friction of the load with c o r r e s p o n d i n g velocity, and is again quickly discharged from the cylinders into the chimney to produce the preceding efi~ct in the increased speed. The absolute power of a locomotive engine is therefore measured by the velocity with which the engine moves~ and a machine which at 15 miles an hour may be called a twenty-horse engine, at 30 miles an hour becomes a forty-horse engine. M a n y singular and important consequences hence present themselves to the engineer; it would lead us too far astray from our general subject to attempt to analyze them; but the practical result is, to add to the other reasons for k e e p i n g railway lines as nearly horizontal as attainable, since the velocity~ and consequently the power of the engine, is greatly diminished when ascending acclivities, from ~everal causes, particularly from the effects of gravity, upon which we shall proceed to remark. The power necessary toovercome the friction that is to move a load, is stated in terms of the load; and so is the power requisite to overcome the effects of gravity, when the line deviates from the horizontal. T h e rise of any such plane is usually expressed by the proportion between the base and perpendicular of the right-angled triangle, of which the inclined plane forms the h)/pothenuse, being an inch, a fool, a yard, g~c. vertical, to so many inches, feei, yards, ~kc. horizontal. Thus, a plane which rises one foot, or any other lineal measure, in 250 feet, or any other number of lineal measures, is said to rise 1 in 250; and the expression of the power requisite to overcome the effects of gravity is being that fraction or proportion of the load; and if the load be one ton~ then the power to overcome the gravity due to a rise of 1 in 250, is nearly 91bs. T h e power requisite on a rise of 1 in ~24, is 10 lbs. per ton; and the power on a rise of 1 in 280, is 8 lbs.; and on a rise of 1 in 300, about 5k lbs.; and so, by dividing the number of pounds in a ton (2240) by the number which expresses the proportion of the base to the perpendicular, of any triangle such as above, being the denominator of the fraction a table may be formed e x h i b i t i n g the power per ton, requisite to overcome the power of gravity on all inclinations, to be added to the friction on ascending planes; and (to a certain extent only however) to be deducted from the friction on deeending planes. In d e s c r i b i n g the gradients of a rail-way~ it is usual to state the rise
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Progress of Civil Engineering.
p e r n d l e in feet, as well as t h e p r o p o r t i o n o f t h e r i s e o r p e r p e n d i c u l a r lift to t h e l e n g t h o r b a s e . I n o r d e r to i l l u s t r a t e m o r e c l e a r l y t h e g r e a t i n c r e a s e of p o w e r r e q u i r e d w h e n i n c l i n a t i o n s o c c u r , we h a v e t h r o w n i n t o a t a b u l a r f o r m t h e force or p o w e r r e q u i r e d to o v e r c o m e t h e frict i o n w h i c h is a c o n s t a n t q u a n t i t y at all v e l o c i t i e s a n d at all slope% a n d t h e force to o v e r c o m e t h e gravity~ w h i c h v a r i e s as t h e line o f t h e a n g l e of i n c l i n a t i o n ; --5--'~-- 7 12 I 16 l 21 50 66 106-"[ Force or powo Ft. per Ft. per Ft. perjFt, per]Ft, perlFt, per Ft. per Ft. per er per ton. ~w:n. Mile. Mile. I Mile. I Mile. / Mile' ] Mile. Mile. Mile, 1 1 / 1 / a / 1 i 1 1 1 I 1 I
lb; lbs. lb, I Ib--T--t lbs---T- lbs. l 3
I 5.1 I 6.8
9
lbs---T-/'lbs. I I /
21 ! 28 I 45
I f t h e f r i c t i o n b e t a k e n at 7~ o r 81bs. p e r ton, o r at 101bs. p e r t o % t h e s u b s t i t u t i o n of t h e s e n u m b e r s w o u l d r e s p e c t i v e l y d e c r e a s e or i n c r e a s e t h e a b o v e totals. ~ T h e i m p o r t a n c e of k e e p i n g r a i l w a y s as n e a r l y l e v e l as p o s s i b l e is self. e v i d e n t f r o m t h i s table. W i t h t h e m e d i u m f r i c t i o n , so s m a l l a rise as 1 in 1000 r e q u i r e s 25 p e r cent. a d d i t i o n a l p o w e r ; w i t h a r i s e of 21 feet p e r m i l e , t h e p o w e r m u s t be d o u b l e d ; a n d on a n e l e v a t i o n of I in 8% w h i c h w o u l d b e s c a r c e l y h e e d e d by t h e t r a v e l l e r o n a r o a d , t h e p o w e r m u s t b e fully q u a d r u p l e d . I t m a y be m e n t i o n e d h e r e , i n c i d e n t a l l y , t h a t t h i s i n c l i n a t i o n of 1 in 80 is c o n s i d e r e d t h e p r a c t i c a l l i m i t for l o c o m o xive e n g i n e s to w o r k u p o n ; a n d w h e n i m p e r a t i v e c i r c u m s t a n c e s c o m p e l t h e a d o p t i o n of s u c h a slop% i t s h o u l d be for a v e r y s h o r t d i s t a n c e . T i l e a v e r a g e f r i c t i o n on m o s t of o u r p r e s e n t t u r n p i k e r o a d s b e i n g ass u m e d at 561bs. to t h e ton, t h e p o w e r is n o t d o u b l e d u n t i l t h e rise bec o m e s 1 in 40~ w h i l e on a r a i l w a y w h o s e f r i c t i o n is 91bs. to t h e t o % t h e p o w e r is d o u b l e d w h e n t h e r i s e is 1 i n ~250. It is t h e r e f o r e a m e r e cor o l l a r y to o b s e r v e , t h a t t h e m o r e p e r f e c t t h e railway~ t h e m o r e i n j u r i o u s are inclined planes. I n d e s c e n d i n g i n c l i n e d p l a n e s the effect o f g r a v i t y is in f a v o u r of t h e load~ a n d is to be d e d u c t e d i u s t e a d of b e i n g a d d e d to t h e f r i c t i o n ; b u t t h e useful effect of gravity~ in t h i s r e s p e c t , on a d e s c e n t , does not e x t e n d b e y o n d t h e a m o u n t o f the f r i c t i o n ; a n d t h e a d v a n t a g e c a n n o t be said to a p p l y to p l a n e s e x c e e d i n g t h o s e on w h i c h t h e g r a v i t y j u s t b a l a n c e s t h e friction~ a n d w h e r e o % if n o f u r t h e r p o w e r w e r e a p p l i e d , t h e load w o u l d * The general result of M'Neil's experiments for measuring the force of traction, or the labour of horses in drawing carriages on different sorts of roads, is as follows: On a gravel road, . . . . . 1:47" lbs.~ ~ 65 ' On a broken stone smfface on all old flint road, • [ ~ ' ~o On ~ broken stone surface upon a rough pavement foundation, 46 ~ .s • F o ; " On a broken stone surface upon a bottoming of concrete formed o f ) , a o Varker's c e m e n t ann ~ra~el .
.
.
.
~ 46
I ~
On an excellent smooth, well-lald pavement, . 33 J ~ .~" And upon a road recently coverecl with a thick layer of broken stones the traction was found as much as 240 lbs. The absolute amount of friction only, of ordinary carriages, is probably not more than 25 lbs., all above that is resistance, more or less, according to the .~tate of the road and weather, and the size and form of the fellers of the wheels.
Traction on Railwags.
49
remain at rest. T h e angle of inclination on which the friction is exactly equivalent, to the gravity, has been hence sometimes called the angle of repose. W h e n the gravity due to the inclination of the plane exceeds the friction, the load will be impelled downwards with a velocity proportionate to the angle of descent. W i t h i n the last twelvemonth a novel doctrine has been broached, founded on some of the precedin~ premises, on which it is necessary to say a very few words. It has been stated, that on two railroads, each one hundred miles in length, the one being perfectly horizontal throughout the whole distance, and the other rising for half the distance, at the rate of 1 in 25% and failing at the same rate for the other half, however such inclinations may be distributed over the line, these two railroads may be worked by the same mechanical power. Nothing can be more absurd or deceptive than to entertain such a fallacy;--like some other mere abstract mechanical propositions, it is toe tally false in practice. More especially is it to be deprecated as applicable to railways worked by locomotive steam-engines,which machines are not constructed (at least at present) to convert their high speed into additional power, with a slower motion, while ascending inclined planes; for~ as has been already observed, their power depends upon the maintenance of their velocity, and it is upon inclined planes the engines lose their speed, and consequently their power, at the very time it is most wanted, and particularly, as in the case in question, on planes of 1 in 250, when their power is required to be doubled. W h a t m i g h t he true theoretically, in this ease c~,n never be obtained practically. T h e theory supposes, that at any moment the additional power requisite, being the double of that required on a level line, can be supplied and given out on the ascent; and that on the descent the whole of the power is saved and economised. A n u m b e r of practical difficulties at once a r i s e ~ s u c h as the slipping of the wheels in unfavourable weather, the diminution of the positive amount of adhesion at all times, the additional wear and tear of the engines, strained to the utmost exertion of their power~ and the extra injury done to the railroad on the inclines, which is even greater on the descent than on the ascent. A m o m e n t ' s reflection will shew that on the descent, the steam, although not given out at the moment~ must necessarily be kept up in the boiler, to be ready for the next piece of level road, or for a start after a stopping, 8~c., and that in the meantime it is blowing off at the safety valve. In order to keep up the velocit?/,which is the great element in railway traveling, tlae load throughout the line, undulating t in 250, must be only one half of what could be carried on the l e v e l , ~ o r a second engine must be ready to help on the ascents, while the first engine must necessarily continue with the train while descending, and nothin.~ is saved in practice but a small quantity of fuel. And if the rise of 1 in 25o were continued in one slope of 50 miles, the equally continuous descent on the other side, though presentin~ an apparent economy of power, would Fequire a third engine to help the return cargo upwards, or the second engine must travel downwards after the train, to be ready to assist the r e t u r n i n g load. So that in practice a double set of engines must be employed, although in theor9 the actual mechanical power is the same upon a level line and on a line risin~ and falling at the rate of 1 in 250. T h e preceding theory having gained ground from the respectable auVOL. X l X . ~ l o . 1.--Jx~uaI~Y~ 1857. 5
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Progress of Civil Engineering°
t h o r i t l e s who have p r o m u l g a t e d it in more than one H i g h Court of Judicature, and in publications of a scientific character~ it has become duty to point out its fallacies~ and to b r i n g the public to distinguish between the abztract amount of mere mechanical fore% and the positive necessity of keeping up the means of supplying additional power when wanted, without the possibility of any real economy, when the actt~al giving out of p o w e r is not required. A n o t h e r m a t e r i a l element in the consideration of locomotive power~ is the load which an engine can draw after it~ not as calculated from the cylinder power of the machine, but from its own weight insistent upon the rails. T h i s has been called the adhesive power nf the engine. T h e amount of this adhesion was long unknown to engineers; and the early history of locomotive engines shews that various contrivances were made and patents taken out~ to effect a greater amount o f adhesion than was supposed to exist. It is now well ascertained, that the amount of adheo sic% that is, the capability of an engine to d r a g a load after it on a railway~ is d e t e r m i n e d greatly by the state of the weather. T h e adhesion of one iron bar sliding on another, is usually estimated at one-seventh of the weight of the bar moved. In a locomotive engin% the adhesion is o r d i n a r i l y allowed to be one-fifteenth of its weight; though, under favourabte circumstances, it is often as much as one-twelfth, or even onetenth~ while it is sometimes so small as a twentieth~ or even a fortieth° T h e adhesion is also diminished in p r o p o r t i o n to the rise of the plane° A s experience has been gained in the practical working of railways, it has been found advisable on many accounts, a m o n g which to acquire adhesion is not the least, that the locomotive engines should be m a d e m u c h heavier than originally constructed. T h r e e , four~ five, and six tons constituted the original limits, which have been successively extended: A n ordinary locomotive engine for level lines, is now never m a d e of less weight than ten tons. As the railways deviate from the horizontal~ a heavier engine to transport a p r o p e r load at a high speed~ becomes necessary; and engines of twelve tons weight may henceforth be considered as likely to become in general use. W e shall~ therefore~ explain the amount of adhesion of such an engine. T h e adhesion, that is, the grip, bite~ or hold~ which the wheels Of a locomotive engine have upon the rail~ has already been stated to be on an average the one-fifteenth p a r t of the weight of the engine. But the whole weight of the engine is only applicable to overcome the loads when the wheels are coupled together; and this is not usually the case, except for assistant engines on inclined planes, and for engines moving at a c o m p a r a t i v e l y slow rate. In those locomotives adapted for high velocities, the fore and hind wheels are not coupled~ and it is only the w e i g h t insistent on the d r i v i n g wheels, that is, the wheels directly acted upon from the cylinders by the: connecting rods, which affords the adhesion. In a twelve ton engine, the w e i g h t on the driving wheel is about two-thirds of the whole weight, say eight tons; and it is one-ill= teenth part of this weight, or, in round numbers, about 12001bs., which~ under the average circumstances of weather, and the state of the rails, is the adhesive power, of such an e n g i n e , ~ t h i s being divided by the friction, viz. 9lb. to the ton, gives about 133 tons as the load which can be d r a w n on a hnrizontal: railway, without the wheels slippir~.% T h e ratio of diminution of adhesion is as the sine of the angle of inclination. On f.rosty mornings~ when the atmosphere is humid~ and the rails covered
T r a c t i o n or~ R a i l w a y s .
5I
with rime, there is scarcely any adhesion, ,particularly on inclines, and the engines are unable to get on, the wheels turn round without advancing, and the steam copiously supplied at the m o m e n t of the first check, is soon blown off, and, however great the cylinder power, the train is totally stopped. I f the wheels of a twelve ton engine are coupled, the whole weight will be available in the computation of the adhesive p o w e r s and the load would be 200 tons. I t will be supposed, that a certain proportion becomes requisite in the construction of a locomotive engine, between the power of adhesion and the cylinder power, which it is only necessary to allude to her% as we have already unconsciously entered into a longer p r e p a r a t o r y description than first intended, having~ indeed, scarcely left ourselves the opportunity of adding a few p a r a g r a p h s on railway curves. The leading distinction in the construction of the wheels of c a r r i a g e s adapted for m o v i n g on railways, and the wheels of road vehicles, is, that the former are fastened to the axletre% which revolves with them, turning in friction boxes of a peculiar kind; whereas, in ordinary carria~es, the axle remains fast, and the wheels revolve thereon: E x p e r i e n c e has taught this to be absolutely necessary for r a i l w a y wheels, especially at high velocities. In order to retain the wheels upon the raised rail, or iron track~ whereon they roll~ the tire is furnished with a projection called the flanch; now universally placed on the inner side of the wheel, and about three quarters of an inch deep. In laying out lines of railway~ curves should be avoided as much as possible; but when this cannot be effected altogether, recourse m u s t be had to means of obviating the effect of the centrifugal force, and of the additional friction of the flanch of the wheel upon the rail, otherwise arising from the circumstance of the wheel being fast upon the axle. The former is counteracted by simply elevating the outer rail or convex side of the railway track according to a simple formula well known to engineers: the radius of the curves taken to the centre of gravity of the load, and the m a x i m u m velocity of the train f o r m i n g the principal elements therein, in connexion with the breadth of the t r a c k : the latter is remedied by allowing some little additional play in the gauge of the wheels, beyond what would be necessary if there were no curves. W h a t is called the cone of the wheel is not applied on account of the curves, but to throw the flanch of the wheel from c o m i n g into contact with the button or edge of the rail generally, t h r o u g h o u t any portion of the road. The perimeter, or bearin~ surface, or tread, of the wheel, being in fact the frustrum of a cone, and the difference of the diameter on the side of the wheel where the fianch is placed, and on the other side, that is, between its whole breadth of about four inches, is about one-eighth of an inch. A n d it is best, if practicabl% to lay the rails so that their surfaces be not perfectly horizontal~ but parallel to the inclination or cone on the wheels, the tread being thereby uniform upon the broad top of the rail, and not partial, as is too often the case, b r e a k i n g down the p r o jecting button or upper web of the rail. T h e exactness with which railway curves are laid out, and the perfect manner in which they become tangential to each other and to the s t r a i g h t parts of the road, form one of the principal cares of the engineer; simple practical rules exist for this purpose, hut they are not often attended to. T h e increased loads and velocities on railways~ requiring engines o f
52
_Progress of Civil Engineering,
greater power and weight, has made it necessary to increase the strength of the iron bars very materially. T h e rails on the Stockton and Darlington line were at first only 28 lbs. to the yard; on the Liverpool and Manchester railway they were 35 lbs. to the yard. On the Dublin and Kingstown road they were 45 lbs. to the yard; and most of the recent railways are constructed with rails of 60 lbs. to the yard, and even 75 lbs. has been tried; but in these last two cases, the bearings or distances between the points of support have been increased from 3 feet to 4. and 5 feet respectively. It would lead into too long and too detailed a paper to attempt here to enter into any discussion as to the mode of laying down a railway, after the necessary excavations and e m b a n k m e n t s are made, and the bridges and other constructions built to restore the existing communications by land and water, so as to isolate the railway as effectually as if it were a river or canal; but we may mention, in general terms, that the more perfect and effectual the system ol drainage, the more efficiently will the road be kept in order, and too much attention cannot be beo stowed on this point. It may also be mentioned as tile opinion of several engineers of much practical experience, that all the previous attempts to make a non-elastic railway have been productive of unprofitable resuits. A railway laid on massive blocks of stone, and secured as completely as art can effect, certainly presents the least resistance to the mere motion of the load; but the successive passage of heavy trains of carriages, at great velocities, and impelled by powerful locomotive engine% soon dislocates the best laid railway; and as it is a continual contest between the i m p i n g i n g force and the resisting road~ a positive amount of wear and tear arises to the engines and carriages, of a much greater extent than may be supposed. The resistance of the non-elastic blocks causes a disorganization of the moving machinery, and thence arises the double destruction of the railway and of the trains moving upon it. It appears also, that the motion of a train of carriages, when passing o,¢er the portions of a railway laid on wood, is much easier to the passengers, and causes less jar on the road, and to the machinery and vehicles; and although a certain positive additional amount of steam power may be required when the railway is somewhat elastic, this is much more than compensated by the saving in the wear and tear. I n pursuance of this idea, experiments have been made, by which it appears that beams or baulks of timber laid longitudinally, and connected occasionally by transverse pieces, to keep the road in gauge, are most likely to be much used for railways, the iron rails being fastened thereon. At the present high price of iron, and in places even where stone is not dear, this mode will be found very economical. T h e barg may be rolled in a particular form; so as to avoid the necessity of using chairs or pedestals to support the rail, which would be laid lengthwise on the wood beams, and having thus a continued support, the bar itself may be made lighter. Rails of 36 to 40 lbs. per yard, would be sufficiently heavy, tht~s affixed. Such railways would require a much smaller expense to keep them in repair, and the softness of the movement thereon, as experience has shewn, would greatly diminish the de~ struction of carriages~ now occasioned by the continual jars on a nonelastic road.
45
,Oatl ./tttrltlon Compound. T o one part of lime water (a saturated solution of lime) add one part of olive oil, unite them well by thorough slitring or agitation, and they form a soapy compound of the consistence of cream. If too weak for the purpose, more oil may be added. This compound is said to be better than pure oil for the lubrication of small works. For cogs or teeth of wheels, whale or common oil may be taken in the proportion of one part to two of lime water. It assumes the consistence of thick paste, when a small quantity of carbonaceous matter, such as plumbago, or soot, may be added and well incorporated. For this compound a patent was taken out in England, by ~ . Partridge, in December, 1835. Lo~. Jour. Arts ~ndSciences. Lubricalion by Water. S i r , ~ I perceive in the report, of the Times, of the proceedings of the scientific meeting at Bristol, that Dr. Lardner suggests placing water-pots before the wheels of a train of railway carriages to reduce the friction. T h e fact of a train running lighter on a wet (lay is well known to every engine driver; and it occurred to me to avail myself of the water leaking from the boiler, or tender~ passing it, in the first instance, into the ash-pan, from which the excess drops in a small jet behind the engine wheels; thus the engine passes over the dry, and the tender and train over the wetted part of the rail. In the event of the boiler being so tight that the leakage would be insufficient, two small tubes, with regulat~ ing cocks, should pass from the tender~ or cistern, and discharge a small j e t on the rails as the train passes along. I shall feel obliged by your insertion of this letter in your earliest Number, in order to advance my title to the priority of this useful adaptation of what would be otherwise lost water. YouFs~ ~c. W . J . CURTIS. Lon.Mee,~{ag.
Progress o f Civil E n g i n e e r i n g . Traction on l~ail-wass. From an article in the Dublin Review, No. 1, (May, 1836) on "The Rail Road S~stem
in Ireland."
A modern R a i l w a y m a y be defined to be a perfect R o a d - - h a r d , dry, and level, presentin~ the least possible resistance from irregularities of surface or inclination. Vehicles p r o p e r l y contrived, and furnished with wheels and axles, peculiarly constructed to move along the iron t r a c k s with the least friction; and the untiring mechanical engine~ compressed into the smallest useful compass~ mounted on a carriag% supplied from a portable boiler~ with steam at a high pressur% and yoked in front of the frame to be moved~ give forth an irresistible power, t r a n s p o r t i n g passengers and merchandize with a speed and economy wholly unattainable by means of animal resources. T h e force necessary to move any given load on a horizontal line, is expressed by writers on mechanics in terms of the load itself. On a, Railway extremely well laid, and in good order~ with the bearing per i m e t e r of the wheels turned perfectly true; with the best fitted axles~ properly lubricated~ and the iron rails clean and dry, or quite wet, the friction is reduced to its lowest terms. By friction is to be understood the sum of the obstruction to the movement of the c a r r i a g e or train of
46
_Progress of Civil Engineering.
carriages, arising from the resistance to the rolling p e r i p h e r y of the wheels as they move along the rails~ and tl~e friction at the axles from the insistent load. T h e amount of resistance is small~ and, supposing the rails Io be clean and in order~ need not~ by the general enquirer, be distinguished fi.om the sum total of the friction. E x p e r i m e n t has satisfactorily proved, that the friction is the same at all velocities. To overcome this frictions or~ in other words~ to overcome the vis inertix of the load, a certain power is requisit% varying somewhat, as will be presently shewn; but which power, on a Railway, is now usually taken to be about ~ 01 t h part of the load, whatever that may be, Now a ton consisting of 2240 lbs. the 5~gth p a r t thereof is 9 lbs. nearly; and it is the ordinary expression in Railway parlance~ to call the triction 9 lbs. to the ton. Some engineers prefer taking 10 tbs. to ~he ton, or ~ s t h part of the loads as the measure of the friction~ in all states of the weather, of the Railway and of the carriages. Otherscon~ sider that 8 tbs. or 5~\6th~ or even 7~ Ibs~ or ~-~z)-thp a r t of the load, to be a sufficient allowance. The above tbrm the extremes for practical purposes; but experiments have been made on c a r r i a g e s , with axles so I~ frl"C tmn, " constructed, and the Railway in such go0d order~ that tlie in one case, appeared to be as small as 2} lbs. to the ton, or --a--th hart 10001 t" of the load; and in some other instances, only 4 or 5 lbs. or ~rv()~h of the load. T h e s e are, however, only interesting as illustrative of what is possibI% under very peculiar circumstances; but like many experiments on models, would lead to false conclusions, and be deceptive, it sta~ed to be true in general practice. U n d e r all the states of road and weather, then, the exertion of a force (animal or mechanical) of 9 or 10 lbs. will move a ton upon a level Railway. Now an ordinary hors% travelling at the rate of about ~ miles an hour, and working 10 hours daily, exerts a force of about 128 lbs. This~ indeed, is a point rather unsettled a m o n g engineers, and a horse-power is usually taken higher; but it is a safe average for all horses. T h e m o m e n t a r y effort of a powerful London d r a y horse is perhaps four or five times what is above assumed~ while a weak, ill-fed animal~ used t h r o u g h a long journey~ would be scarcely equal to half the above effect. A n ordinary horse can tak% however, about 14 tons along a level Railway, at the rate of ~ miles an hour~ working all (lay; but the power of an animal to draw is diminished as he is driven more rapidly. A horse capable of travelling 1~ miles per hour, would only draw 3 tons on a level Railway at that velocity, and could not continue to do so any length of time. T h e application of animal power is therefore very limited, and it is to steam recourse has been had, to obtain high velocities. T h o u g h it is t¢'ue that the friction s and of course the power, requisite to move the dead weight~ is the same at all velocitie% yet the velocity itself is only obtained in the ratio with which the power to o v e r c o m e the friction of the load is supplied. In a locomotive steam engine, of the best modern construction, the velocity may he defined in a general way, to he regulated by the b o i l e r - p o w e r ~ t h a t is, the capability of the boiler to supply steam~ of effectively high pressure, with sufficient rapiditys so as to enable the pistons to make a greater number of strokes per minute, thereby t u r n i n g the wheels round a greater number of times~ and of course u r g i n g the machine to a h i g h e r speed. So the load which the same engine can draw, supposing it to have sufficient adhesion on the rails,
TraeHon on Rail-ways.
47
may be expressed to be regulated by 'the d i a m e t e r of the cylinders, the pressure of the steam, and the length of the stroke of the piston, from which elements are obtained a certain expression of value in lbs. called the cylinder-power, which, divided by 8, 9, or 10 lbs. as the friction may he assumed, gives the number of tons which the engine is capable of drawing. T h i s is by no means a scientific, and perhaps not a strictly correct description; but it will convey an a p p r o x i m a t e idea of the power and effect of the locomotive engine, which is all that is necessary on the present occasion. The most r e m a r k a b l e circumstance in the application of steam-power on railways, is the mode in which the steam, having done its duty in the cylinders of the eng'ine, is discharged up the chimney, and entering therein under a pressure still considerably h i g h e r than the atmospheric pressure, produces a m o m e n t a r y vacuum; this is followed by a rush of air from the flues or tubes of the boiler, thus creating a great draught from the furnace, and, by d r a w i n g the heated air in the increased velocity t h r o u g h the tubes~ generates steam in the boiler with proportionate rapidity. T h i s steam supplies the force to overcome the friction of the load with c o r r e s p o n d i n g velocity, and is again quickly discharged from the cylinders into the chimney to produce the preceding efi~ct in the increased speed. The absolute power of a locomotive engine is therefore measured by the velocity with which the engine moves~ and a machine which at 15 miles an hour may be called a twenty-horse engine, at 30 miles an hour becomes a forty-horse engine. M a n y singular and important consequences hence present themselves to the engineer; it would lead us too far astray from our general subject to attempt to analyze them; but the practical result is, to add to the other reasons for k e e p i n g railway lines as nearly horizontal as attainable, since the velocity~ and consequently the power of the engine, is greatly diminished when ascending acclivities, from ~everal causes, particularly from the effects of gravity, upon which we shall proceed to remark. The power necessary toovercome the friction that is to move a load, is stated in terms of the load; and so is the power requisite to overcome the effects of gravity, when the line deviates from the horizontal. T h e rise of any such plane is usually expressed by the proportion between the base and perpendicular of the right-angled triangle, of which the inclined plane forms the h)/pothenuse, being an inch, a fool, a yard, g~c. vertical, to so many inches, feei, yards, ~kc. horizontal. Thus, a plane which rises one foot, or any other lineal measure, in 250 feet, or any other number of lineal measures, is said to rise 1 in 250; and the expression of the power requisite to overcome the effects of gravity is being that fraction or proportion of the load; and if the load be one ton~ then the power to overcome the gravity due to a rise of 1 in 250, is nearly 91bs. T h e power requisite on a rise of 1 in ~24, is 10 lbs. per ton; and the power on a rise of 1 in 280, is 8 lbs.; and on a rise of 1 in 300, about 5k lbs.; and so, by dividing the number of pounds in a ton (2240) by the number which expresses the proportion of the base to the perpendicular, of any triangle such as above, being the denominator of the fraction a table may be formed e x h i b i t i n g the power per ton, requisite to overcome the power of gravity on all inclinations, to be added to the friction on ascending planes; and (to a certain extent only however) to be deducted from the friction on deeending planes. In d e s c r i b i n g the gradients of a rail-way~ it is usual to state the rise
48
Progress of Civil Engineering.
p e r n d l e in feet, as well as t h e p r o p o r t i o n o f t h e r i s e o r p e r p e n d i c u l a r lift to t h e l e n g t h o r b a s e . I n o r d e r to i l l u s t r a t e m o r e c l e a r l y t h e g r e a t i n c r e a s e of p o w e r r e q u i r e d w h e n i n c l i n a t i o n s o c c u r , we h a v e t h r o w n i n t o a t a b u l a r f o r m t h e force or p o w e r r e q u i r e d to o v e r c o m e t h e frict i o n w h i c h is a c o n s t a n t q u a n t i t y at all v e l o c i t i e s a n d at all slope% a n d t h e force to o v e r c o m e t h e gravity~ w h i c h v a r i e s as t h e line o f t h e a n g l e of i n c l i n a t i o n ; --5--'~-- 7 12 I 16 l 21 50 66 106-"[ Force or powo Ft. per Ft. per Ft. perjFt, per]Ft, perlFt, per Ft. per Ft. per er per ton. ~w:n. Mile. Mile. I Mile. I Mile. / Mile' ] Mile. Mile. Mile, 1 1 / 1 / a / 1 i 1 1 1 I 1 I
lb; lbs. lb, I Ib--T--t lbs---T- lbs. l 3
I 5.1 I 6.8
9
lbs---T-/'lbs. I I /
21 ! 28 I 45
I f t h e f r i c t i o n b e t a k e n at 7~ o r 81bs. p e r ton, o r at 101bs. p e r t o % t h e s u b s t i t u t i o n of t h e s e n u m b e r s w o u l d r e s p e c t i v e l y d e c r e a s e or i n c r e a s e t h e a b o v e totals. ~ T h e i m p o r t a n c e of k e e p i n g r a i l w a y s as n e a r l y l e v e l as p o s s i b l e is self. e v i d e n t f r o m t h i s table. W i t h t h e m e d i u m f r i c t i o n , so s m a l l a rise as 1 in 1000 r e q u i r e s 25 p e r cent. a d d i t i o n a l p o w e r ; w i t h a r i s e of 21 feet p e r m i l e , t h e p o w e r m u s t be d o u b l e d ; a n d on a n e l e v a t i o n of I in 8% w h i c h w o u l d b e s c a r c e l y h e e d e d by t h e t r a v e l l e r o n a r o a d , t h e p o w e r m u s t b e fully q u a d r u p l e d . I t m a y be m e n t i o n e d h e r e , i n c i d e n t a l l y , t h a t t h i s i n c l i n a t i o n of 1 in 80 is c o n s i d e r e d t h e p r a c t i c a l l i m i t for l o c o m o xive e n g i n e s to w o r k u p o n ; a n d w h e n i m p e r a t i v e c i r c u m s t a n c e s c o m p e l t h e a d o p t i o n of s u c h a slop% i t s h o u l d be for a v e r y s h o r t d i s t a n c e . T i l e a v e r a g e f r i c t i o n on m o s t of o u r p r e s e n t t u r n p i k e r o a d s b e i n g ass u m e d at 561bs. to t h e ton, t h e p o w e r is n o t d o u b l e d u n t i l t h e rise bec o m e s 1 in 40~ w h i l e on a r a i l w a y w h o s e f r i c t i o n is 91bs. to t h e t o % t h e p o w e r is d o u b l e d w h e n t h e r i s e is 1 i n ~250. It is t h e r e f o r e a m e r e cor o l l a r y to o b s e r v e , t h a t t h e m o r e p e r f e c t t h e railway~ t h e m o r e i n j u r i o u s are inclined planes. I n d e s c e n d i n g i n c l i n e d p l a n e s the effect o f g r a v i t y is in f a v o u r of t h e load~ a n d is to be d e d u c t e d i u s t e a d of b e i n g a d d e d to t h e f r i c t i o n ; b u t t h e useful effect of gravity~ in t h i s r e s p e c t , on a d e s c e n t , does not e x t e n d b e y o n d t h e a m o u n t o f the f r i c t i o n ; a n d t h e a d v a n t a g e c a n n o t be said to a p p l y to p l a n e s e x c e e d i n g t h o s e on w h i c h t h e g r a v i t y j u s t b a l a n c e s t h e friction~ a n d w h e r e o % if n o f u r t h e r p o w e r w e r e a p p l i e d , t h e load w o u l d * The general result of M'Neil's experiments for measuring the force of traction, or the labour of horses in drawing carriages on different sorts of roads, is as follows: On a gravel road, . . . . . 1:47" lbs.~ ~ 65 ' On a broken stone smfface on all old flint road, • [ ~ ' ~o On ~ broken stone surface upon a rough pavement foundation, 46 ~ .s • F o ; " On a broken stone surface upon a bottoming of concrete formed o f ) , a o Varker's c e m e n t ann ~ra~el .
.
.
.
~ 46
I ~
On an excellent smooth, well-lald pavement, . 33 J ~ .~" And upon a road recently coverecl with a thick layer of broken stones the traction was found as much as 240 lbs. The absolute amount of friction only, of ordinary carriages, is probably not more than 25 lbs., all above that is resistance, more or less, according to the .~tate of the road and weather, and the size and form of the fellers of the wheels.
Traction on Railwags.
49
remain at rest. T h e angle of inclination on which the friction is exactly equivalent, to the gravity, has been hence sometimes called the angle of repose. W h e n the gravity due to the inclination of the plane exceeds the friction, the load will be impelled downwards with a velocity proportionate to the angle of descent. W i t h i n the last twelvemonth a novel doctrine has been broached, founded on some of the precedin~ premises, on which it is necessary to say a very few words. It has been stated, that on two railroads, each one hundred miles in length, the one being perfectly horizontal throughout the whole distance, and the other rising for half the distance, at the rate of 1 in 25% and failing at the same rate for the other half, however such inclinations may be distributed over the line, these two railroads may be worked by the same mechanical power. Nothing can be more absurd or deceptive than to entertain such a fallacy;--like some other mere abstract mechanical propositions, it is toe tally false in practice. More especially is it to be deprecated as applicable to railways worked by locomotive steam-engines,which machines are not constructed (at least at present) to convert their high speed into additional power, with a slower motion, while ascending inclined planes; for~ as has been already observed, their power depends upon the maintenance of their velocity, and it is upon inclined planes the engines lose their speed, and consequently their power, at the very time it is most wanted, and particularly, as in the case in question, on planes of 1 in 250, when their power is required to be doubled. W h a t m i g h t he true theoretically, in this ease c~,n never be obtained practically. T h e theory supposes, that at any moment the additional power requisite, being the double of that required on a level line, can be supplied and given out on the ascent; and that on the descent the whole of the power is saved and economised. A n u m b e r of practical difficulties at once a r i s e ~ s u c h as the slipping of the wheels in unfavourable weather, the diminution of the positive amount of adhesion at all times, the additional wear and tear of the engines, strained to the utmost exertion of their power~ and the extra injury done to the railroad on the inclines, which is even greater on the descent than on the ascent. A m o m e n t ' s reflection will shew that on the descent, the steam, although not given out at the moment~ must necessarily be kept up in the boiler, to be ready for the next piece of level road, or for a start after a stopping, 8~c., and that in the meantime it is blowing off at the safety valve. In order to keep up the velocit?/,which is the great element in railway traveling, tlae load throughout the line, undulating t in 250, must be only one half of what could be carried on the l e v e l , ~ o r a second engine must be ready to help on the ascents, while the first engine must necessarily continue with the train while descending, and nothin.~ is saved in practice but a small quantity of fuel. And if the rise of 1 in 25o were continued in one slope of 50 miles, the equally continuous descent on the other side, though presentin~ an apparent economy of power, would Fequire a third engine to help the return cargo upwards, or the second engine must travel downwards after the train, to be ready to assist the r e t u r n i n g load. So that in practice a double set of engines must be employed, although in theor9 the actual mechanical power is the same upon a level line and on a line risin~ and falling at the rate of 1 in 250. T h e preceding theory having gained ground from the respectable auVOL. X l X . ~ l o . 1.--Jx~uaI~Y~ 1857. 5
50
Progress of Civil Engineering°
t h o r i t l e s who have p r o m u l g a t e d it in more than one H i g h Court of Judicature, and in publications of a scientific character~ it has become duty to point out its fallacies~ and to b r i n g the public to distinguish between the abztract amount of mere mechanical fore% and the positive necessity of keeping up the means of supplying additional power when wanted, without the possibility of any real economy, when the actt~al giving out of p o w e r is not required. A n o t h e r m a t e r i a l element in the consideration of locomotive power~ is the load which an engine can draw after it~ not as calculated from the cylinder power of the machine, but from its own weight insistent upon the rails. T h i s has been called the adhesive power nf the engine. T h e amount of this adhesion was long unknown to engineers; and the early history of locomotive engines shews that various contrivances were made and patents taken out~ to effect a greater amount o f adhesion than was supposed to exist. It is now well ascertained, that the amount of adheo sic% that is, the capability of an engine to d r a g a load after it on a railway~ is d e t e r m i n e d greatly by the state of the weather. T h e adhesion of one iron bar sliding on another, is usually estimated at one-seventh of the weight of the bar moved. In a locomotive engin% the adhesion is o r d i n a r i l y allowed to be one-fifteenth of its weight; though, under favourabte circumstances, it is often as much as one-twelfth, or even onetenth~ while it is sometimes so small as a twentieth~ or even a fortieth° T h e adhesion is also diminished in p r o p o r t i o n to the rise of the plane° A s experience has been gained in the practical working of railways, it has been found advisable on many accounts, a m o n g which to acquire adhesion is not the least, that the locomotive engines should be m a d e m u c h heavier than originally constructed. T h r e e , four~ five, and six tons constituted the original limits, which have been successively extended: A n ordinary locomotive engine for level lines, is now never m a d e of less weight than ten tons. As the railways deviate from the horizontal~ a heavier engine to transport a p r o p e r load at a high speed~ becomes necessary; and engines of twelve tons weight may henceforth be considered as likely to become in general use. W e shall~ therefore~ explain the amount of adhesion of such an engine. T h e adhesion, that is, the grip, bite~ or hold~ which the wheels Of a locomotive engine have upon the rail~ has already been stated to be on an average the one-fifteenth p a r t of the weight of the engine. But the whole weight of the engine is only applicable to overcome the loads when the wheels are coupled together; and this is not usually the case, except for assistant engines on inclined planes, and for engines moving at a c o m p a r a t i v e l y slow rate. In those locomotives adapted for high velocities, the fore and hind wheels are not coupled~ and it is only the w e i g h t insistent on the d r i v i n g wheels, that is, the wheels directly acted upon from the cylinders by the: connecting rods, which affords the adhesion. In a twelve ton engine, the w e i g h t on the driving wheel is about two-thirds of the whole weight, say eight tons; and it is one-ill= teenth part of this weight, or, in round numbers, about 12001bs., which~ under the average circumstances of weather, and the state of the rails, is the adhesive power, of such an e n g i n e , ~ t h i s being divided by the friction, viz. 9lb. to the ton, gives about 133 tons as the load which can be d r a w n on a hnrizontal: railway, without the wheels slippir~.% T h e ratio of diminution of adhesion is as the sine of the angle of inclination. On f.rosty mornings~ when the atmosphere is humid~ and the rails covered
T r a c t i o n or~ R a i l w a y s .
5I
with rime, there is scarcely any adhesion, ,particularly on inclines, and the engines are unable to get on, the wheels turn round without advancing, and the steam copiously supplied at the m o m e n t of the first check, is soon blown off, and, however great the cylinder power, the train is totally stopped. I f the wheels of a twelve ton engine are coupled, the whole weight will be available in the computation of the adhesive p o w e r s and the load would be 200 tons. I t will be supposed, that a certain proportion becomes requisite in the construction of a locomotive engine, between the power of adhesion and the cylinder power, which it is only necessary to allude to her% as we have already unconsciously entered into a longer p r e p a r a t o r y description than first intended, having~ indeed, scarcely left ourselves the opportunity of adding a few p a r a g r a p h s on railway curves. The leading distinction in the construction of the wheels of c a r r i a g e s adapted for m o v i n g on railways, and the wheels of road vehicles, is, that the former are fastened to the axletre% which revolves with them, turning in friction boxes of a peculiar kind; whereas, in ordinary carria~es, the axle remains fast, and the wheels revolve thereon: E x p e r i e n c e has taught this to be absolutely necessary for r a i l w a y wheels, especially at high velocities. In order to retain the wheels upon the raised rail, or iron track~ whereon they roll~ the tire is furnished with a projection called the flanch; now universally placed on the inner side of the wheel, and about three quarters of an inch deep. In laying out lines of railway~ curves should be avoided as much as possible; but when this cannot be effected altogether, recourse m u s t be had to means of obviating the effect of the centrifugal force, and of the additional friction of the flanch of the wheel upon the rail, otherwise arising from the circumstance of the wheel being fast upon the axle. The former is counteracted by simply elevating the outer rail or convex side of the railway track according to a simple formula well known to engineers: the radius of the curves taken to the centre of gravity of the load, and the m a x i m u m velocity of the train f o r m i n g the principal elements therein, in connexion with the breadth of the t r a c k : the latter is remedied by allowing some little additional play in the gauge of the wheels, beyond what would be necessary if there were no curves. W h a t is called the cone of the wheel is not applied on account of the curves, but to throw the flanch of the wheel from c o m i n g into contact with the button or edge of the rail generally, t h r o u g h o u t any portion of the road. The perimeter, or bearin~ surface, or tread, of the wheel, being in fact the frustrum of a cone, and the difference of the diameter on the side of the wheel where the fianch is placed, and on the other side, that is, between its whole breadth of about four inches, is about one-eighth of an inch. A n d it is best, if practicabl% to lay the rails so that their surfaces be not perfectly horizontal~ but parallel to the inclination or cone on the wheels, the tread being thereby uniform upon the broad top of the rail, and not partial, as is too often the case, b r e a k i n g down the p r o jecting button or upper web of the rail. T h e exactness with which railway curves are laid out, and the perfect manner in which they become tangential to each other and to the s t r a i g h t parts of the road, form one of the principal cares of the engineer; simple practical rules exist for this purpose, hut they are not often attended to. T h e increased loads and velocities on railways~ requiring engines o f
52
_Progress of Civil Engineering,
greater power and weight, has made it necessary to increase the strength of the iron bars very materially. T h e rails on the Stockton and Darlington line were at first only 28 lbs. to the yard; on the Liverpool and Manchester railway they were 35 lbs. to the yard. On the Dublin and Kingstown road they were 45 lbs. to the yard; and most of the recent railways are constructed with rails of 60 lbs. to the yard, and even 75 lbs. has been tried; but in these last two cases, the bearings or distances between the points of support have been increased from 3 feet to 4. and 5 feet respectively. It would lead into too long and too detailed a paper to attempt here to enter into any discussion as to the mode of laying down a railway, after the necessary excavations and e m b a n k m e n t s are made, and the bridges and other constructions built to restore the existing communications by land and water, so as to isolate the railway as effectually as if it were a river or canal; but we may mention, in general terms, that the more perfect and effectual the system ol drainage, the more efficiently will the road be kept in order, and too much attention cannot be beo stowed on this point. It may also be mentioned as tile opinion of several engineers of much practical experience, that all the previous attempts to make a non-elastic railway have been productive of unprofitable resuits. A railway laid on massive blocks of stone, and secured as completely as art can effect, certainly presents the least resistance to the mere motion of the load; but the successive passage of heavy trains of carriages, at great velocities, and impelled by powerful locomotive engine% soon dislocates the best laid railway; and as it is a continual contest between the i m p i n g i n g force and the resisting road~ a positive amount of wear and tear arises to the engines and carriages, of a much greater extent than may be supposed. The resistance of the non-elastic blocks causes a disorganization of the moving machinery, and thence arises the double destruction of the railway and of the trains moving upon it. It appears also, that the motion of a train of carriages, when passing o,¢er the portions of a railway laid on wood, is much easier to the passengers, and causes less jar on the road, and to the machinery and vehicles; and although a certain positive additional amount of steam power may be required when the railway is somewhat elastic, this is much more than compensated by the saving in the wear and tear. I n pursuance of this idea, experiments have been made, by which it appears that beams or baulks of timber laid longitudinally, and connected occasionally by transverse pieces, to keep the road in gauge, are most likely to be much used for railways, the iron rails being fastened thereon. At the present high price of iron, and in places even where stone is not dear, this mode will be found very economical. T h e barg may be rolled in a particular form; so as to avoid the necessity of using chairs or pedestals to support the rail, which would be laid lengthwise on the wood beams, and having thus a continued support, the bar itself may be made lighter. Rails of 36 to 40 lbs. per yard, would be sufficiently heavy, tht~s affixed. Such railways would require a much smaller expense to keep them in repair, and the softness of the movement thereon, as experience has shewn, would greatly diminish the de~ struction of carriages~ now occasioned by the continual jars on a nonelastic road.