1841.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 383 



S\ipplementary paper, On the Momentum proposed by Mr. Joslah Paries, 

 as a measure of the Mechanical effect of Locomotive engines. By the Count 

 (le Pamboiir. 



In a former paper, inserted in the Civil Engineer and Architect's Journal, 

 for September last, we have proved that all the strictures presented by Mr. 

 Parkes, in his paper: On steam boilers and s/ram enymes, inserted in the 

 Transac/i'ins of the Institution of Civil Engineers, vol. ill., against some of 

 the experiments of our Treatise on Locomotive Engines, are entirely founded 

 upon errors of his own ; and, besides, that his momentum or intended 

 "standard" of the mechanical effect of locomotive engines, which he pro- 

 poses to substitute in place of every other research on the same subject, leads 

 him to conclusions and results altogether faulty. 



However, as in a letter inserted by Mr. Parlies in several periodicals 

 {Literary Gazette, September 18th, Mining Journal, ismc date. Civil Engi- 

 neer and .irchitect's Journal for October), he complains that in answering 

 his strictures, we have misrepresented his sentiments, we shall now add a 

 few more observations, to show that we have not misrepresented the senti- 

 ments of Mr. Parkes; and, besides, that it is not upon sentiments, but upon 

 facts, that we can establish clearly that the whole of the calculations and 

 tables of Mr. Parkes are erroneous, and, as every one of his conclusions and 

 strictures are founded upon tlie numbers obtained in his tables, tliat every 

 one of his conclusions and strictures are equally erroneous. 



For that purpose we shall resume, in the same order, all the articles of our 

 former paper, quoting more particularly the facts, or the expressions of Mr. 

 Parkes, upon which is grounded our refutation. 



1st. We have said that, to calculate the mean pressure of the steam in the 

 cylinder of each of the engines submitted by us to experiment, Mr. Parkes 

 uses the average velocity of the whole trip between Liverpool and Manches- 

 ter. This fact cannot be denied, and is made quite evident by looking at his 

 table viii. column 10, table xiii. col. 9, table xvi. col. 2, in which the veloci- 

 ties are headed, mean velocity of the engines jier hour, and are in fact the 

 average velocities of our experiments, given page 1 75 of the Treatise on Lo- 

 comotive Engines, 1st edition, and page 253, 2nd edition ; with the exception 

 only of the cases in which Mr. Parkes has increased the velocities, from a 

 pretended correction of his own, of which we shall speak in a moment. 



Now, in recurring to our former paper, same article, it will be seen that 

 such mode of calculating the pressure in the cylintlcr, from the average or 

 mean velocity of the whole trip, is altogether faulty : because it gives only 

 the pressure which would have taken place, if the whole trip bad been per- 

 formed at a uniform velocity. But the velocity varied considerably in the 

 different portions of the trip, according to the more or less inclination of the 

 part of road traversed by the engine, as may be seen in our detailed table of 

 those experiments (pages 225 to 234, 1st edition, and pages 389 to 394, 2!id 

 edition of the Treatise on Locomotive Engines). And in taking account, as 

 ouglit to be done, of the time during which each partial velocity has been con- 

 tinued, we have proved, in our former paper, that the real mean pressure in 

 the cylinder, is very different from the pressure given in Jlr. Parkes's calcula- 

 tion. We can, therefore, safely conclude that the pressures, and correspondent 

 volumes, of the steam in the cylinder, presented by ilr. Parkes as the results 

 of his computation, are altogether faulty. 



2nd. Me have shown a first error, which Mr. Parkes introduces, as a funda- 

 mental basis, in all his calculations, and which has nothing to do with his 

 sentiments. But he does not stop there. We have said that, moreover, he 

 increases almost all the velocities nearly i ; and to be assured of this, it again 

 suffices to compare, in his paper, table viii. col. 10, table xiii. col. 9, table 

 xvi. col. 2, with our own table ]iage 175, 1st edition, and page 253, 2nd edi- 

 tion, of the Treatise on Locomotive Engines. It will be found that the velo- 

 city of Vulcan, in experiment VI. i table viii. of Mr. Parkes), is increased from 

 22'99 to 26'90 miles per hour, that of I'esta, in experiment V, from 27'23 to 

 31'60 miles per hour, that of .Mas, in experiment III, from 15-.j3 to IS'15 

 miles per hour, that of 4tlas in experiment IV, from 20-59 to 24-07 miles 

 per hour, that of Leeds, in experiment VIII, from 21-99 to 26-/0 miles per 

 hour, that of Fury, in experiment IX, from 18-63 to 21-79 miles per hour, 

 and that of Fury, in experiment X, from 21-99 to 2300 miles per hour. So 

 that, out often experiments extracted from our work, seven have been made 

 entirely false by this alleged correction to the observed velocities ; and this 

 is worse than if the whole of them had been falsitied in the same manner, as 

 it would, at least, have left the same proportion between the results. Mr. 

 Parkes makes the same addition to the observed velocities, and therefore in- 

 troduces the same error, in calculating the experiments of .Mr. E. Woods, 

 with the Ilecia, since we find (page 112) : 



" Mean velocity during the trip 29-4 7 miles per hour. 



" Differetice for gradients 1-46 ,, 



" Mean velocity on a level 30-93. 



Mr. Parkes falls into this error, because, in speaking of fuel, it is said, in our 

 Treatise on Locomotive Engines (jia^Q 324, 1st edition, and page 311,2nd 

 edition), that when the engines ascend without help one of the two inclined 

 planes of the Liverpool and Manchester Railway, tlie surplus of work, thence 

 resulting for them, equals, on an average, the conveying of their load to about 

 ^ more distance ; that is to say that the engine will, in that case, consume 

 as mwQhfnel as if it had conveyed an equal load to a distance greater by ^, 

 on a level. And the critic thence logically concludes (page 86) that the ve- 

 locity must be by so much increased, without perceiving that this correction 

 refers only to the work done, and, as a consequence, to the corresponding 



consumption of fuel, but not to the velocity, which would suppose, not only 

 that the load has been conveyed to ^ more distance, but, besides, that it has 

 been conveyed there in the same time. 



Respecting this mistake, we have also proved that the error of Mr. Parkes 

 has the double consequence of increasing the pretended effect produced, and 

 lowering the pretended pressure of the steam in the cylinder ; so that the 

 proportion between the power applied and the effect produced is made doubly 

 erroneous, and introduced so in his tables. 



All this is certainly undeniable, and rests upon tables and facts only, not 

 upon sentiments, and when we say that the whole of the calculations and 

 tables of Mr. Parkes are grounded upon those mistakes, it cannot be denied 

 either, in looking only at table viii. col. 10, table ix. col. 19, table xiii. col. 9, 

 table xiv. col. 3, table xvi. col. 2. It will be there seen that everg other 

 column is depending upon the alleged velocity of the engines. Therefore, we 

 are right when we conclude that the volume and pressure of the steam con- 

 sumed by the engines (table ix. col. 26, 29), the horse power produced per 

 cubic foot of water vaporized, or the quantity of water and coke employed to 

 produce one horse power (table x. col. 44, 45, 49, &:c.), the momenta gene- 

 rated per second (table xiii. col. 11, 12, table xiv. col. 9, 10, 11), and finally 

 all the consequences derived from the comparison of the results obtained in 

 those tables, about the alleged inaccuracy of the experiments, or the respec- 

 tive effects of loconmtive and fixed engines, arc in everj- way erroneous. 



To show, by a particular example, the fallacy of the results to whicli Mr. 

 Parkes has been led by this wholesale and faulty way of calculating, with a 

 wrongly averaged and greatly exaggerated velocity, without taking account 

 of the gravity, or of any of the other resistances really encountered by the 

 engines, we refer to the two experiments of Fury, of which Mr. Parkes says 

 (page 128), " a reference to the Fury (previously adverted to as giving ano- 

 malous results) exhibits that engine as having performed more work at 23 

 than at 215 miles per hour, by the ratio of 24 to 19 ; it is therefore with 

 certainty we may conclude one or both of those experiments to be erroneous." 

 We have shown that this consequence presented by the critic with such cer- 

 tainty, proceeds only from bis having neglected to consider that one of the 

 experiments was made from Manchester to Liverpool, and the other, on the 

 contrary, from Liverpool to Mancbester. But, on account of the general ris- 

 ing of the road from Manchester towards Liverpool, the gravity opposes more 

 resistance in that direction than in the other. So that, .ilthough the load of 

 the engine was lighter in the first trip, stiU there was more work required of 

 the engine, to convey that load to the other end of the line. In fact, in 

 making the calculation as it ought to be, that is to say in taking account of 

 the gravity overlooked by Mr. Parkes. it is found that, in the trip made from 

 Manchester to Liverpool, the work done liy the engine amounted to convey- 

 ing 1964 tons to one mile, or 65-5 tons to 30 miles, on a level, and in the 

 other trip, to 1837 tons to one uule, or 60-6 tons to 30 miles, on a level. 

 Therefore the engine ought to have employed more time in performing the 

 first trip than the second, which, concurrently with the other errors of com- 

 putatioi\ of Mr. Parkes, had led him to conclude with " certainty" these ex- 

 periments to be erroneous. 



3rd. Mr. Parkes (pages 82, 83) says, " the pressure deduced from the sum 

 of the resistances, given in column 29, for M. de Pambour's experiments I. to 

 X, is composed, 1st of the friction of the engine without load, which includes 

 the resistance opposed to it as a carriage, in comuion with the train; 2ndly, 

 of the additional friction brought upon the engine by the load; 3rdly, of the 

 resistance of the load at 8 lb. per ton. According to the author, these three 

 items include all the resistance overcome by the steam, excepting that occa- 

 sioned by the blast, in excess over the atmosphere. The amount of the latter 

 shotdd, therefore, be ascertainable by comparing the whole force exerted by 

 the steam on the piston, with the force assigned as requisite to overcome the 

 aforesaid tliree, out of the four component parts of the total resistance. The 

 difference between these pressures should represent the precise amount of the 

 counter elasricity of the steam in the blast-pipe." So, it is clear, as we have 

 said in our former paper, that Mr. Parkes calculates the pressure owing to 

 the blixst-pipe, merely by taking the difference between the valuation of the 

 divers resistances and his own result of the pressure of the steam in the cylin- 

 dei-. Now, we have already proved that this last result, obtained by .Mr. 

 Parkes as representing the pressure in the cylinder, is altogether erroneous. 

 Tlierefore his supputation of the pressure in the blast-pipe must equally be 

 60. But, besides, it is evident that such a mode of proceeding, by merely 

 taking the difference between two assumed quantities, to establish the value 

 of a third unknown, coidd never give, for this one, a value siitficiently certain 

 to make it the test of experiments ani facts; since every thing neglected in 

 the calculation, like water lost by priming, resistance of the air. gravity, &c. 

 would necessarily pass to the account of the pressure due to the blast-pipe, 

 and falsify it. Consequently, if, by tins calculation, Mr. Parkes is led to very 

 inaccurate results, he ought not to be astonished, and we are not certainly. 



4th. Mr. Parkes (pages 98, 99), in speaking of our two experiments made 

 with the engine Leeds, says : " the author also has informed us that in the 

 two experiments, the pressure in the l)oiler was precisely the same, and the 

 regulator opened to the same degree. The power applied in the two cases 

 was, consequentlv, preciselv equal, and equal weights of water as steam passed 

 through the evlinders in equal times ; whence it rcstdts that the effects should 

 have been sim'ilar. The expenditure of power was, however, greater by more 

 than a third in the second than in the first case, to produce like effects, for 

 we see that the effective horse power required 85-43 lb. of water as steam in 

 the second and only 60-94 lb. in the first." And (page 100), " if, as asserted, 



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