1839.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



385 



in the diagram ; and in every case a uniform velocity was obtained, — tliis 

 \elocity diminishing witli tlie sleeiniess of the phice. 



Wiieii these first exjierimeiits hecame kno\\'ii, one of the olijcctions lirought 

 against them was., tliat a train of four coaclies was so light, tliat a moderate 

 atmosplieric resistance ^i'oiild retard it; and that as, in tlie practical worli- 

 ing of railways, such trains were never used, the results obtained liad no 

 practical utility ; and tliat with hca\T trains, such as tliose actually used on 

 railways, no such results wmdd ensue. This olijeclion, among others, was 

 ailvanced in a Report piililislied hy Mr. lirmiel, the engineer of the Great 

 Western Railway. In order lo meet this ohjeetion, trains of greater magni- 

 tude were subsequently tried, and the same results ensued — a uniform 

 M-locily being attained in every case in which the train could be started 

 from tlie top of the iilaiic with a sufficiently high sjieed. In the following 

 T.able I, is exhibited tlie ine.an results of a vast number of experiments tried 

 with trains of four, six, and eight coaches. In the third column, the letter 

 expresses generally the state of the wind — F fair, A adverse, C moderately 

 calm, and CO a dead calm ; the fourth column gives the gradient down 

 which the motion took place' ; and in the last column is expressed, in miles 

 jier hour, the uniform velocities which the train attained, and which it pre- 

 served through a lengtli of the plane sufficiently considerable to show that 

 it would not have received any further increase. 



Table I. 



The last experiment with a train of eiglit coaches, weighing nearly forty 

 tons, shows that, in a dead calm, the resistance of that train at Z\\ miles 

 on liour amounted to the eif/hti/-iiinlli part of its weii/til ; w/iereas the com- 

 mon estimate of tlie resistance of snch a train at tliat s^jei'd has been hitherto 

 ahaxit the 2a0th part of its weiyht .' This fact alone, were it unconnected 

 with any others, would sufficiently illustrate the enormous extent of eiTor 

 which has prevailed hitherto in such estimations in railway practice. The 

 tbiril experiment with eight carriages was made with a side wind, the effect 

 of which is abundantly innnifested by the speed expressed in the last column. 

 While the same train, moving with a fair mud down the Madeley plane, 

 had a resistance equal to the 177tli of its weight, at 26 miles an hour, its 

 resistance with a side wind was of greater amount at 17.7 miles an hour. 

 The relative effects of a fair and adverse wind, are likew ise exhibited in the 

 third and fourth experiments with six coaches, down the Whiston plane. 

 The velocity, which gives a resistance equal to the 9Gth part of the load, 

 was 34 J miles an hour with a fair wind, and only 27J with an adverse 

 wind. 



WHien the first ex|)erimenfs indicating these results became puliUc, various 

 objections were urged against them by Mr. Brunei ; and altliough it was 

 not considered by Ur. Lardner, or by any of the other persons engaged in 

 this inquiry, that such objections were entitled to any serious attention, yet 

 it was thought ailvisablo to make experiments which would show whether 

 or not they had any foundation in truth. One of these objections was 

 the following: that the circnmslances under which such experiments were 

 performed, were not really, though they were aiiparcntly, similar to those 

 of an ordinary train in motion; that the carriages were here sent with the 

 square end foremost, to meet and receive the full resistance due to their 

 snrface, which is totally different from the case in which the engine pre- 

 cedes them. The engine in front, it was stated, would act as a sort of 

 rut-air or bow, and thus destroy or diminish the resistance produced by the 

 flat front of the carriages moving foremost. In oriler to ascertain the full 

 value of this objection. Dr. Lardner took an engine, ' The Fury,' with her 

 tender, and obtained two coaches, weighted so as to be nearly equal in 

 weight to the engine and tender. The connecting rods and working-gear 

 of the engine were detached from the driviiu; wheels, so that the engine 

 should be subject to no other friction save that which a coach is subject to. 

 The Fury and its tender, and these two coaches, thus prepared, were placed 

 successively at the summit of the Sutton plane, falling ^j'g towards IManches- 

 ter, and the Liverpool and .Manchester Railway: and they were allowed to 



descend by gravity. The circumstances of their descent were found to be, 

 in all respects, alike, jiassing corresponding stakes at very nearly the same 

 time, and very nearly the same speed. The full particulars of this, and other 

 exiieriments, wdl be published: but, in the meanwhile, the principal results 

 of this experiment are exhibited in Table 41 : — 



Table II. 



It ajipears, therefore, that the difference in the whole distance run by the 

 coaches, and by the engine and tender, amounted lo only 133 yards, in a 

 distance little short of three miles ; and that there was only three seconds 

 difference in the time. The maximum speed attained was nearly the same ; 

 •and the time of descending the inclined plane only differed by five seconds. 

 This difference, such as it was, was in favour of the coaches with their flat 

 front. In fact, the ditrcrences of the numbers in the successive columns of 

 the above table, are only such as would take place in the same experiment 

 tried twice successively with the same coaches. 



As a second test, the engine and tender was now placed in front of four 

 coaches, so as to form a regular train, and it was allowed to descend the 

 jilane in the same manner. The engine and tender was then removed, and 

 replaced by two coaches of equal weight, and the train of six coaches was 

 then allowed to descend the plane in the same way. The residt of the ex- 

 periment is exhibited in Table III. 



Table III. 



It is needless to enlarge upon these results. The plain and inevitable in- 

 ference is, and that inference would be further corroborated by what he had 

 still to explain, — that the form of the front, whether flat or sharp, has no 

 observalde effect on the resistance ; and that whether the engine and tender 

 be in front, or two carriages of the same weight as the engine and tender, the 

 motion of the train, and the resistance to its motion, will be exactly the same. 



The form of a boat, or lieak, having been given to some of the engines 

 on the Great Western Railway, apparently with a view to diminish the effect 

 of the atmospheric resistance. Dr. Lardner determined to ascertain how far 

 such a form would produce any practical efl'ect. He accordingly constructed 

 a head or beak, to place before the first carriage of a train. Two boards 

 were constructed equal in height to the body of the caniage, and being 

 attached to each corner, were united in fixnit at an angle, the vertex of the 

 angle being five feet six inclies before the flat front of the carnage, and the 

 base of the angle being six feet six inches, corresponding with the width of 

 the carriage. This apparatus would have the efi'cct of a cut -air. It was 

 first tried with a single coach, which, having it attached in front, was moved 

 as before down the Sutton plane, and the circumstances of the motion 

 having been onserved and recorded, the beak was removed, and the coach 

 again moved do\\n with the flat end exposed to the air. The result was as 

 follows : — 



Table IV. 



2 I 2 



