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THE CIVIL KNGINI'ER AND ARCHITECTS JOURNAL. 



[September, 



peiiments were made ou tlie Grand Junction inclines ; and the result of the 

 whole shows the existence of an opposing power, created at it were by the 

 speed itself, far exceeding that liitlierto suspected. 



A train of eight carriages weigliing lOi tons was started down the Madely 

 incline 1 in 17", at speeds varying from 23 to 20 miles per hour; the mean 

 speed attained was 2.')J miles per hour. Tlie motion of the train became 

 uniform, so that the coefficients of gravity and resistance were eipial. The 

 mean resistance of the train was 12.\ tb. per ton. A train of four carriages 

 was started down the incline at 10 miles per honr, half way down the jilane 

 the velocity was reduced to .30 miles per hour, and at the foot, it was only 

 2.5 miles per honr. Four other carriages were started at a velocity of 32-7 

 miles per hour, they were retarded to 227 miles per hour, and proceeded 

 with this uniform velocity to the foot of the incline. The results obtained 

 in these experiments with the trains of eight carriages are of great practical 

 importance, this being the nearest api)roach to the average passenger trains. 

 30 miles per hour is a fair average speed, and the resistance at the speed is 

 about 1.') th. per ton, or almost double the value of the friction only. The 

 friction may be diminished by proper attention to the fittings and the perfect 

 lubrication of the axles, but its reduction is of secondary importance in the 

 economic working of passenger traijis, which, from their high velocity, must 

 necessarily bring into play large and independent sources of resistance. The 

 resistance to trains at different speeds being ascertained, the Committee di- 

 rected their attention to the effect of external configuration on the resistance. 

 A pointed body, as a prow, was fixed successively to the front and 

 end of a train, but the diflerences obseived were extremely slight, and such 

 only as would have occurred with the same experiment repeated twice over; 

 the pointed figure, whether before or behind, exercised no appreciable in- 

 fluence ou the rate of the train's motion, or on the resistance of which that 

 motion is the index. Experiments were also instituted, to ascertain whether 

 the carriages being sent with their square enils forward, instead of being pre- 

 ceded by an engine and tender, would affect the results, but here also there 

 were no greater differences than njigbt be expected in an experiment repeated 

 twice over; and it may be fairly concluded, that the form of the front has 

 no observable effect, and that whether the engine and tender be in front, or 

 two carriages of etiual weight, the resistance will be the same. The inter- 

 mediate spaces between the carriages were closed in, by stretching strong 

 canvas from carriage to carriage, thus converting the wiiole train into one 

 unbroken mass. The results were in favour of the train without canvas, but 

 the difyorences are extremely slight ; it is certain that no additional resistance 

 is occasione<l by leaving ojjcn spaces between the carriages, confining the 

 intervals to the dimensions allowed in practice. 



The Committee having ascertained that the excess of resistance, after de- 

 ducting friction, required for its estimation something besides the elements 

 of the dimensions and form of frontage, and of continuity of surface, it be- 

 comes imjiortant to inquire, what is the element exei ting so powerful an in- 

 fluence ? Their former Rejiort contains the results of experiments with wagons 

 on the Madely incline loaded to six tons each, and furnished with boarded 

 fronts and sides moveable at pleasure; the diflerences in the results attained, 

 were then referred to the increased frontage alone. But the experiments 

 detailed in the present Report liaving been made, it became probable that the 

 increased resistance was in a great measure dependent on the general volume 

 of air displaced ; and the Committee recommend experiments to be directed, 

 to ascertain the effect on the resistance of diminishing and increasing the 

 bulk of trains, the weight remaining the same. 



Experiments were also made with the view of determining the amount of 

 moving power expended in working a line, and for this purpose, the character 

 of the hne, in respect of its inclines, the weight and bulk of the train, and 

 the speed at which tlie load is required to be conveyed, must be considered. 

 The first of these alone is constant, de)iending on the nature of the acclivities 

 and declivities. As an abstract question of dynanics, the power expended 

 (the resistances being supjiosed constant, whatever the speed) is the same for 

 a train travelling between two points on the same level, whether the road he 

 be level or undulating, a dne allowance being made for the difference of dis- 

 tance traversed. On the level li?ie of railway, the speed of travelhng would 

 be uniform, but on the undulating line it would vary. And the real question 

 is, will the increased velocity on the declivities compensate for time lost on 

 the acclivities? Will the average rate of speed over the whole line he difie- 

 rent .' In order to obtain some definite result on the point, it was determined 

 to_ send a train from Liverpool to Uirniingham and back, a distance of lltO 

 miles. Great care was taken in conducting this experiment, and the results 

 are tabulated in great detail ; and the following remarkable inference may be 

 drawn, that a train of 12 carriages di.awn by the same engine can be convev- 

 cd over a railway whose gradients range within the specified limits, in the 

 same time as it could over a perfectly level railway of the same length. In 

 ordinary practice, an engine of the dimensions tried (the Ilecla) would re- 

 ceive assistance up the Sutton, Whiston, and Warrington inclines (1 in 8!t. 

 90, and 80), but this was not the case in flic experimental trip, and the train 

 encountered acclivities and declivities not contemplated in the appUcation of 

 this theory. It may therefore be inferred that the oi)inion entertained was 

 correct, or that trains whose weights bear an ascertainable relation to the 

 nature of the inclines they have to traverse, may be made to tr.averse those 

 inclines at an average sjieed equal to what the power of the engine can effect 

 on a level, and that an ordinary train would travel over the Grand Junction 

 Railway (the steeper inclines of I in fO being excepted) in as short a time as 

 if the line had been absolutely level. 



Mr. Brunei remarked on the inapplicability of results obtained from trains 

 running down inclines to the ordinary working of trains on railways. Many 

 of the residts given ifi the Report differ exceedingly from the results of his 

 experience in the woiking of the Great Western Railway. The cause of this 

 discrepancy arose from the manner in which the resistances were obtained. 

 In the train of caniages running down an incline, each carriage is slightly 

 pressed upon by the next behind, so that the whole train is in the condition 

 of a train that is pushed ; and it is well known that the resistance of a train 

 pushed from behind is much greater than of the same train pulled from be- 

 fore, as the carriages are thrown out of square. — Alhenifum. 



" Remarka on the Connexion vliicli exists between Improvements in Pit- 

 work and llie Duty of Steam-etiginen in Cornwall." By Mr. Enys. 



After adverting to the admission of the truth of progressive increase of 

 duty, it was shown that considerable changes have been made in the course 

 of seventy years, in the methods by which water is lifted out of tlie mines in 

 Cornwall ; and that in comparing the duty of earlier periods, an allowance 

 of the difference of the Imperial and Winchester bushel of coal ought to be 

 made. The distinction between horse-power and duty, pointed out by Mr. 

 Parkes, was alluded to; one excludes, the other includes, the friction of the 

 pitwork ; and the remarks attached to each in Lean's report, show the ne- 

 cessity of adverting to the different conditions of the pitwork, in an attempt 

 to estimate with accuracy the reliitive merit of different engines separate 

 from the pitwork. In an endeavour, some time ago, to trace the causes of 

 the great variation of the duty, a small amount of expansion was observed in 

 engines remarkable for a low duty, and the reasons assigned were, either 

 weak pitwork — flat rods — heavy load per square inch on the piston, and old 

 boilers — and often the joint action of the above causes. The strength of 

 the pitwork, or of ihe boilers, in different cases, seems to become the limit 

 of expansion in the engines. In reference to deficiency of water from pumps, 

 in proportion to the calculated quantities, on which duty is founded, two 

 causes have operated in inducing a strong belief that it is less than at any 

 former period : 1. Greater attention to the pitwork by the managers of the 

 mines, under whose care it is placed, to the exclusion of the engineers of the 

 steam-engine by which it is worked; 2. The extended use of the plunger 

 pump — the latter instantly showing the slightest defect of the packing, and 

 allowing of an easy remedy ; while the bucket pump, on the contrary, does 

 not show the defects in the packing; and the operation of tightening it is 

 attended with great difficulty, so much so, as often to cause the repairing to 

 be delayed to the last moment that the jiunip will lift water. The first 

 cause, though it has a tendency to decrease duty in proportion to imjiroved 

 water delivery, has in a still greater degree the tendency to reduce the fric- 

 tion of the pitwork on a given load ; yet it is not easy to assign the exact 

 values. Oil the whole, a reduction of total resistances probably occurs in 

 shafts of equal depth. On the other h.ind, the great increased depth of 

 many shafts obviously produces a greater proportional friction on a given 

 load. Under these circumstances, it becomes the fairer method to select the 

 duty of engines working the deepest shafts, for a comparison w ith the duty 

 of the earlier periods, when engines were worked so differently as regards 

 the steam. Mr. J. W. Henwood (Wlieal Towan) estimates the deficiency of 

 water delivery at 7 or S per cent. ; Mr. T. Wicksteed (E. Holmbush) 10 per 

 cent, water from three lifts measured and weighed ; Mr. Enys (Eldon's en- 

 gine, United Mines), -1 per cent., measured four strokes of the engine from 

 one plunger lift, i'he absence of attention in earher times can only be as- 

 sumed from tlie known habits of the miner, and the absurd stories prevalent 

 of particular instances of neglect. Another great, but altuost inappreciable 

 change, has occurred within the last ten or fifteen years, in the increase of 

 weight in the rods for a given load ; but the circumstance of the greater 

 weight of such rods again allowed of the reciprocal action of a still greater 

 amount of expansion in Watt's engines ; and in the heavy pitwork, the accu- 

 mulated force stored up .it the commencement was restored at the end of the 

 stroke ; the only loss in duty arises from an increase of the friction of the 

 necessary balance weight ; because, while a direct gain is obvious, the same 

 mean power, by a greater amount of expansion, is obtained from a smaller 

 quantity of water expended as steam. The present form of rod, with lifts 

 alternately, where the shaft admits of this method, was probably dne to Wat, 

 or Murdoch. Smeaton, at the Ch.icewater .\tmospheric Engine, in 1775t 

 seems to have effected the introduction of one rod for a portion of the shaft, 

 and dispensed with the older practice of tying up to the arch of the beam a 

 separate lod for each lift. The plunger pump seems to have effected another 

 change of some importance, in the velocity with which the larger portion of 

 water is raised. The engines are usually made to go, out of doors, at rather 

 more than half the velocity of the in-door stroke, the piston moving in-door, 

 from 240 to 200 feet, and out of doors from 14t to 156 feet per minute; 

 the velocity of the plunger, or bucket, is usu.ally four-fifths of these amounts, 

 or 110 to i20 feet per minute. Still a jiortion of the water, from one-third 

 to one-sixth, is laised at three-fourths of the higher velocity ; and receutly 

 larger valves have been placed below the plunger than above, with a view of 

 equalizing the resistance of the water on passing the valves. A few experi- 

 ments of trying an engine in-doors at a very low velocity have been made, 

 wliich may jierhaps be extended, to determine the increase of pressure due 

 to different velocities of water in the pumps. The column of mercury, how- 

 ever, only becomes the measure of the total resistances of all kinds, which 

 are subsequently, as far as practicable, to be separated, and values assigned 

 to each as nearlv as our means of observation admit. In commencing mo- 



