1844.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



209 



LOSS OF POWER WITH DIFFERENT WEIGHTS OF TRAIN. — TaBLE VI. 



la this table those trains are selected from the experiments detailed in the 

 large table, (3,) which present the most uniform and valuable results. 



We now come to what we consider the practical part of the report ; 

 Mr, Stephen.son proceeds — 



Having now, I trust, cleirly explained the abject and results of the experiments insti- 

 tuted upon the Kingstowu and Dalkey Railway, I will proceed to draw a comparison 

 between tlie working of the atmospheric system, and of other descriptions of motive 

 power which liave long been in use, witli the view of showing their relative advantages or 

 disidvantages. For this purpose I have selected the stationary engines at Camden Town, 

 because they present a case which is similar to that at Kingstown; or, at all events, the 

 disparities are not such ai will materially interfere vvitli the comparison. Table No. VII. 

 represents the gradients and length of the Eustoii iucline, witli the weight of the rope 

 there used, the dimensions ol' the engines, and a description of the various trains tha t are 

 most commonly drawn uj* the incline; the total power given out by the stationary engines 

 13 then given, and divided into the power absorbed by the resistance of the engines, rope, 

 train, and atmosphere, separately, from which are deduced the proportioo of loss arising 

 from this application of the rope as a means of communicating motive power. 



TABLE No. VII. 



The constant upon which this table is faunded, au average gradient -j-^ ; length 

 worked by rope O'iH mile; weight of rope 7 tons; area of both cylinders of engine, 21104 

 square inches, and velocity of pistons 224 feet per minute. 



Statwnary Engines and Ropes. 



Before I proceed to institute any comparison between the results presented in this 

 Table, and those obtained by the experiments on the Atmospheric Railway, I am anxious 

 fully to explain the data upon which the former are based, and the more so, as all the re- 

 sults are calculated, with the exception of the power absorbed by the friction of the en- 

 gines, and of the rope. An indicator was applied to the Camden Town engines, to ascer- 

 taiu this amount, and from these result'* we arrive at the fact that about 53 h. p. is 

 required for working the engines and drawing the ro[ie alone, at a velocity of 20 miles per 

 hour. From experiments upon the friction of the engines and machinery on the Black- 

 wall Railway, where there is the opportunity of disconnecting the rope and drums, and 

 taking the proportions of the power on the two railways, I Jiave considered 13 h. p. of 

 this to be due to the friction of the engines and machinery, which leaves 45 h. p. for the 

 friction of the rope. 



The friction of the several trains taken at 101b. per ton, added to the gravity due to the 

 average gradient, is multiplied into the velocity previously mentioned of 20 miles per iiour, 

 and expressed in horses' power in the Table. The power absorbed by the resistance of 

 the atmosphere is calculated from the experiments of Lardner, previously referred to. 

 The total power given out by the engin^s is thus obtained, from which is deducted the 



power required to overcome the friction of the engines and machinery, for the purpose of 

 making a more correct comparison with ilie power expended on the Atmospheric Railway 

 at Kingstown, as in that case the power required for this purpose is also omitted. The 

 power required to work the rope in the cases specified amounts to a loss varying from H9 

 to 1" per cent, of the total, decreasing as the weight of the train is .mgmented. 



In proceeding to compare with these the results of the experiments on the Atmospheric 

 Railway, it is my object to select a case in etch, which shall present the closest analogy 

 in the amount of their resistance and velocity. The 4th train in Table No. VH., and the 

 Ibth in Table No. VI. correspond very closely in these particulars, the total resistance of 

 the former, including the friction, gravity, and resistance of atmosphere, being equal to 

 102 h. p., and of the latter 100 h. p., and the respective vdocities being 20 and 18 miles 

 per hour. The loss of pon'er from the working of the rope in the former case is equal to 

 ;jO per cent, of the tutal, while the loss rn the latter, arising from raising the vacuum, 

 leakaee, and imperfections of the apparatus, amounts to 74 per cent, of the total power. 

 In order, however, t > institute a correct comparison between these two cases, the total 

 power in the former must be increased in the proportion of the mean to the maximum 

 velocity, which in this Instance is ascertained, from experiments made, to add o" h. p. to 

 the total, and the comparison stands thus : the loss of power on the Euston incline 

 amounts to 45 per cent., while that on the Kin>;stown and Dalkey Hiiilway is 74 per cent. 

 This result is obtained with a train which represents the average working of the Euston 

 inchne ; it is therefore evident that iu this particular instance the rope is very consider- 

 ably more economical than the atmnspheric system. If we assume other weights of train, 

 we siiall perceive, that as they become lighter the proportion of loss by the atmospheric 

 apparatus will be diminished on account of the reduction in the effect o"* leakage accom- 

 panying the reduction in pressure, but the proportion of loss by the rope will be increased 

 as the power required to work the rope itself is the same with a light as with a heavy 

 train ; while on the other hand, with heavier trains the proportion of loss by the rope will 

 be diminished, and that by the atmospheric system greatly augmented, from the increased 

 effect of the leakage, and the additional power required to raise the vacuum to a greater 

 height. 



This comparison may be carried further by examining the quantity of fuel consumed per 

 day on these two lines; and this I am enabled to accomplish trom the observation of a fort- 

 night's working of the Euston incline, and from an experiment on the Kingstown and Dalkey 

 Railway, in which the number of trains, the exact weight of each, and the c->nsumptioa of 

 fuel, was ascertained during an entire day. The result of the Ibrmer was, that 1.'^ trains 

 avera£;ing 44 tons each, the mean resistance of which amounted to ISltOlb., were drawn up 

 the incline of 0*91 mile length, at a mean velocity of about 17 miles per hour, in one day of 

 io hours, with a consumption of iiO cwt. of coal; and the result of the latter was that tea 

 trains averaging 44 tons each, the mean resistance of which amounted to 129.) lb., were 

 drawn up the incline of 1"22 mile length, at a mean ve'ocity of about 14 miles per hoar, 

 in one day of eight hours, with a consumption of 29 cwt. of coal. The consumption of 

 cojI per mile ot the trains in these two cases amounts to 284 lb. on the Euston incline, 

 and 2*3t) lb. at Kingstown ; and dividing these by their respective amounts of irietion and 

 gravity, we obtain the comparative consumption per lb. oi tractive force as '18 lb. in the 

 former case, and '21 lb. in the latter. 



The result of this c^omparison corresponds very closely with the previous compaiison 

 of h. p. and the slight inconsistency is accounted for by the circumstance that I have 

 not taken into consideration the times the fires were alight, the different construction of 

 the engines, &c. But these I have purposely omitted, as it was not my object to 

 enter into a comparison of {letails, but only to illuatrate generally the main features of 

 the working of the two systems > and this cannot fail to be interesting, inasmuch as it is an 

 instance which allows of a fair parallel being drawn between the two systems of motive 

 power, the amount of work performed in the two cases being nearly alike, and the trains 

 in each being drawn only in one direction, descending in the other direction by the force 

 of gravity. If, however, we take some of the trains which are drawn up the Euston" 

 incline, amounting to fully 100 tons weight, we shall find that the total resistance exceeds 

 the caoacity of the tube which is employed at Kingstown namely, 16 inches diameter; 

 for supposing the pressure to be equal to 22 inches height of the barometer, or 1 libs, 

 per square inch, the train just named upon the gradient of 1 in 75, which is near the 

 upper end of the Euston incline, and continues for about one-third of its length, ivould 

 otfer a resistance, at a velocity of 17 miles per hour, of about 4500 lb., and would there- 

 fore require a tube of 23 inches uiameter. 



Such an increase of tube, it must be observed, immediately implied a great reduction of 

 velocity with the atmospheric system, or an increased size of air pump, involving a cor- 

 responding increase of power, because the ratio between the areas of the air pump and 

 vacuum tube is affected j and it has been clearly shown that, working at a high vacuum in 

 a small tube, or increasing the size of the tube and lowering the vacuum, if tiie same 

 amount of power be employed, involves equally the sacrifice of velocity. Here we per- 

 ceive a decided proof, that what is termed good gradients is not a matter of indifference 

 to the atmospheric system, and that we shall not be justified in attribunng to it the p^wer 

 of economising the construction of railways to any considerable extent by avoidiiig th^ 

 necessity of levelling the face of the country. 



By the comparisons we have entered into, we see, that in the case of the Euston inc'ire, 

 a rope is considerably more economical as a means of conveying motive power than a 

 vacuum tube; but if the incline were increased to a length of 3 or 4 miles, this would 

 become rery questionable, as ttie loss of power from the friction of the rope iucreases 

 exactly in the proportion of the length ; but in the atmospheric system the loss from the 

 leakage does not increase so rapidly, as a large portion of it arises from the air pnmp and 

 tube piston, and is the same with all lengths of tube. This it was my intention to have 

 illustrated by referring to the circumstances of the Blackwall Railway, which is a case 

 deemed by the inventors of the atmospheric system peculiarly advantageous for its aj^ili- 



