1841.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



307 



Thus this new peremptory condition wliicli tlie experiments ought 

 to satisfy is as unfounded as the former ones; and, in fact, Jlr. Parkes 

 contradicts it, himself, a little further on (pages 157, loS), so that we 

 might have referred liis first argument to his second, for refutation. 

 But, besides the foregoing observations it must be borne in mind that 

 the velocities employed by Mr. Parkes, for locomotive engines, being 

 nearly all considerably augmented, as has been explained above, he 

 must necessarily arrive (pages So, ST, S9, 92, and tables x., xiii., xiv., 

 xvi.), at exaggerated results, for the effects wliich he supposes to have 

 been produced by those engines; and therefore his comparison be- 

 tween locomotive and stationary engines, is altogether founded upon 

 false calculations. 



It is remarkable, finally, that in applying the preceding considera- 

 tions to all the experiments published on locomotive engines, by difte- 

 rent engineers, namely, Messrs. R. Stephenson, N. Wood, E. Woods, 

 and Dr. Lardner (pages 102, 117, 118, 159), Mr. Parkes finds that the 

 conditions to which he proposes to subject those experiments are not 

 verified in them. Such a result ought to have put him on his guard 

 against the validity of his own arguments ; but the want of knowledge 

 in the principles of Mechanics and of habit in mathematical reasoning 

 (the author tells us that he is more accustomed to handle the hammer 

 than the pen), causes him to heap errors on errors, combining and 

 complicating them unawares, till he arrives at a point where he does 

 not produce a single result that is not erroneous. 



There is a matter of surprise in the numberless errors contained in 

 the paper of Mr. Parkes, and of which, for the sake of brevity, we 

 have noticed merely the principal ones, reserving the rest for another 

 opportunity if necessary. But on inquiring what was the end he had 

 proposed to himself, what was to be definitive consequence of his 

 labour, one is yet much more surprised. 



His object is to propose a new measure of the effect of locomotive 

 engines; and this new measure is what he calls the "momentum" 

 generated, that is to sav, " the product of the mass, in tons, of the 

 engines, tender and train, multiplied into its velocity, in feet per 

 second." This standard is to "represent the repective mechanical 

 effect produced per second by each engine" (page 12S). 



Now, the true mechanical produce includes the whole of the 

 resistances and frictions really overcome by the engines; that is to 

 say, the friction of the carriages, the friction of the engines, the gravity 

 of the mass on the different inclines traversed, the atmospheric pres- 

 sure, the pressure due to the blast-pipe, the resistance of the air, &c. ; 

 and in multiplying the sum of all these resistances, by the velocity of 

 the motion, we shall have the mechanical ef!'ect produced. But, if 

 among all those divers resistances, we take account only of the friction 

 of the carriage, and the engine, omitting all the rest, and if we suppose, 

 for an instant, that friction to be 6 lb. per ton, as well for the engine 

 as for any other carriage, we shall have the effect produced, in multi- 

 plying tlie weight of tlie train, tender and engine included, first by G 

 lb., and afterwards by the velocity of the motion. Now, it is evident 

 that in calculating thus, we shall have exactly the same number given 

 by the computation of Mr. Parkes, excepting that all of them shall be 

 multiplied by 6. Therefore, the new measure proposed comes merely 

 to this, that the effect of the engines will be calculated by the friction 

 of the carriages only, and that of the engine considered as a mere 

 wagon, and the results divided by 6. 



But, as this pretended "standard" comprehends only a portion of 

 the resistances really overcome; as it does not include the gravity of 

 the train, which may, according to circumstances, offer a resistance 

 exceedingly great, or null, or even act in favour of the motioii; as it 

 does not include the counter-pressure due to the blast-pipe, which 

 varies according to the velocity, the rate of vaporization and the size 

 of blast-pipe; as it does not include the total friction of the engine, 

 but only the friction of its wheels, as a single wagon ; as, above all, it 

 does not include the resistance of the air, which, from experiments of 

 •which Mr. Parkes is "utterly ignorant" (page 12-1), varies according 

 to the bulk of the train and the square of the velocity, so that the 

 quantity neglected, on that account, in the calculation may, at times, 

 be quite trifling, and at other times, exceed the momentum of Mr. 

 Parkes itself; as in fact this pretended new measure is nothing more 

 or less than the common useful effect of the engine, as given in many 

 works and particularly in our T/ieory of the Steam Engine, and Trea- 

 tise on Locomotive Engines, with these differences only that in Mr. 

 Parkes's calculation, it includes also the weight of the engine, and that 

 it is erroneously computed, inasmuch as, in multiplying the weight of 

 the train, in tons, by the velocity, the calculation is made as if the 

 whole weight were raised up in the air by the engines, instead of being 

 dragged or rolled along the rails; as, finally, this pretended standard, 

 instead of being constant, varies with the velocity, just as well as 

 what Mr. Parkes calls the commercial and mtfid effects, so that it is 

 not more easy to know the one than the others, or that the rule of Mr. 



Parkes, which we are going to quote, refers to the one just as well a^ 

 to the others; fur all those reasons, then, we see that the aforesaid 

 measure is not new, that it does not measure the mechanical effects of 

 the engines, and finally that it is nothing more or less than the common 

 useful ettect (weight of engine included), calculated in considering the 

 whole train raised up in the air and the engine as a mere wagon. 



After having thus found upon reasoning the accuracy of his new 

 measure of the mechanical elfect of the engines, Mr. Parkes proceeds 

 to show the "powers of this method of analysis" (page 131). Col- 

 lecting all the erroneous results which he has obtained in his tables, 

 and admitting then, as accurate, the experiments of the Treatise on 

 Locomotive Engines, which he thought of demonstrating false before, 

 Mr. Parkes forms a table in which tie sets in view, on one side, the 

 vaporization effected by the engine, and on the other side the useful 

 effect produced, giving it only the name of momentum when it includes 

 the weight of the engine besides that of the wagons, Then comparing 

 the vaporization to the eft'ect produced, and taking an average, not 

 upon his own experiments, since he has made none, but upon all tha 

 experiments which he has collected from the divers works published 

 on the subject, he presents (page 130), as the result of his labours, the 

 following conclusion, which he proposes to substitute in place of every 

 other kind of research on locomotive engines. 



When the velocity of a locomotive engine is augmented in the pro- 

 portion of 1-52 to 1, the vaporization necessary to produce the same 

 effects varies in the following proportions : 



To produce an equal momentum (an equal useful effect, weight of 

 wagons and engine included), in the proportion of 1-42 to 1, or in a 

 proportion something less than that of the velocities ; to produce an 

 equal commercial gross effect (an equal useful effect, including the 

 weight of the wagons), in the proportion of 2-43 to 1, or nearly as the 

 square of the velocities; to produce the same (iSf/uZ effect (the same 

 useful elfect, net weight), in the proportion of 3-11 to 1, or nearly as 

 the cubes of the velocities. 



This is the definitive result which Mr. Parkes has attained, and the 

 help of which seems to him to render it needless henceforward to seek 

 to determine either the friction of the wagons, or that of the engines, 

 or the resistance of the air, or any thing in fact that may influence the 

 effects produced ; researches which appear to him to offer insurmount- 

 able difficulties. Possessed of the niholesale result of Mr. Parkes, no- 

 thing more will be needed. Does any one wish, for instance, to know 

 what load a given engine will draw at 25 miles per hour, on a given 

 inclination ? to know what velocity it will assume with a load of 60 

 tons ? to know what is the maximum of useful effect that it is capable 

 of producing ? to know what proportions must be given to it, in order 

 to obtain desired effects? Why, having recourse to Mr. Parkes's re- 

 sult, the solution of all these questions is self-evident! 



It is evident, on the contrary, that Mr. Parkes's result, even were it 

 exact instead of being founded on erroneous calculation, could lead to 

 but one thing, namely, to find the useful effect produced by an engine 

 at the velocity of 30 miles per hour, when the same effect, in quite 

 similar circumstances, is known at the velocity of 20 miles. But, 

 even then, making use of so rough an approximation, in which all is 

 thrown in the lump : friction of the wagons, friction of the engine, re- 

 sistance of the air, resistance owing to the blast-pipe, &c., the result 

 could never be depended on. Assuredly, calculations like these do 

 not tend to the progress of science ; they would rather lead it back to 

 its first rudiments. For this reason we persist in our belief that the 

 only means of calculating locomotive engines, is to endeavour to deter- 

 mine, as exactly as possible, each of the resislances which oppose their 

 motion, and by taking an account of the value of those forces in the 

 calculation, we may then in every case attain a valuation really founded 

 in principle, of the eHects of every kind that are to be expected from 

 them. 



MR. RANKIN'S WOOD PAVEMENT. 

 (Mridged from the Polytechnic Journal.) 



This new wood pavement is the invention of Mr. Rankin, and 

 manufactured by Messrs. Esdailes and Margrave at their City saw- 

 mills. We will first proceed to describe the process of its manufac- 

 ture from the beginning. A square-sided piece of timber, of a proper 

 length, is provided, each side being four inches across. By the ap- 

 plication of the steam machinery at the saw-mills, two equilateral 

 grooves are rapidly cut along the whole length of the piece. As soon 

 as this operation is performed, the piece is turned completely over, 

 and on the side immediately opposite to that previously grooved, two 

 tongues are cut, in like manner, along its whole length. 



2 T 2 



