1843.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



171 



rated ; he believed that as a simple comparison of the friction of the main 

 parts of two kinds of engines, the results arrived at in the paper might he 

 received as correct ; but there were several other questions which must he 

 considered, if it was intended to establish a general comparison between the 

 beam and the direct action engines ; this, however, he believed was not the 

 intention of the author. 



Mr. Murray contended that the second proposition in the paper, which 

 assumed that' " friction was independent of the area of the rubbing surface," 

 although supported by Coulomb and the early experimenters, bad been 

 proved^ by Vince and others to be incorrect ; it was natural to suppose that 

 in proportion to the hardness and smoothness of bodies, there would exist 

 a different ratio for the best proportion of surface to weight for every diffe- 

 rent body ; if a surface carrying a given weight was of less than the due area, 

 the surfaces would cut into each other, become rough, and thus increase the 

 friction ; on the other hand, if the surfaces were unduly enlarged, there must 

 be a loss from the additional amount of friction caused by the extended sur- 

 face. He conceived that the calculations in the paper must be affected by 

 the incorrectness of the data upon which they were based. The simple mode 

 of comparing the beam engine with the direct action engine appeared to be, 

 to suppose two engines of the same length of stroke and diameter of cylinder; 

 the proportions being good, it would be indifferent whether the power was 

 transmitted through a direct connecting rod or through side levers ; the 

 cylinders, air pump, arrangement of parallel motion, &c, being supposed to 

 be alike, the friction of these parts would be alike in all cases, and the com- 

 parison would be limited to the parts employed in transmitting the power 

 from the piston rod cross head to the crank pin ; both connecting rods have 

 the same number of bearings, which in both cases travel with friction over 

 nearly the same distances : it is allowed that the bearings of the shorter con- 

 necting rod have a larger amount of friction, and that from the greater angle 

 it assumes, more friction is thrown upon all the bearings of the parallel mo- 

 tion, on account of the greater force required to retain the piston in a vertical 

 position. To counterbalance the increased friction on these parts of the 

 direct acting engine, allowance must be made in the beam engine for the 

 friction of the beam centres and of the top and bottom necks of the side rods. 

 The friction being directly as the distance moved through, and the distance 

 in the side red ends being so very small, it follows that the amount of friction 

 must be very trifling. The distance travelled by the beam centres is greater, 

 but it is not of importance, as it is the angular distance due to the vibration 

 of the beam, measured on the circumference of the gudgeon. Under these 

 considerations Mr. Murray was disposed to give the preference (if any ex- 

 isted) to the side lever engine. In a pamphlet 4 published in 1840, by Mr. 

 John Seaward, it is stated that four-fifths of the whole friction of an engine 

 were absorbed by the packings of the piston and air-pump bucket, by the 

 slide valves and by the different packings or glands ; consequently one fifth 

 was due to the whole of the necks or bearings throughout the engine. Now 

 on considering the large proportion of this amount of the friction that is due 

 to the hearings of the main shafts, of the crank pin, and of the bottom end 

 of the connecting rod, and of all those other bearings common to both sorts 

 of engines, it must be evident that the total amount of the friction due to 

 those parts in which a difference between the engines exists, must be but a 

 small portion of this one-fifth. Taking one-tenth or ten per cent, of the 

 whole power of an engine, as the amount of power required to overcome the 

 friction of the engine itself, which was allowed to be ample, one- fifth of this 

 would be two per cent., and therefore the degree in which either engine could 

 surpass the other in the amount of friction, could only be, as already stated, 

 a small portion of this two per cent. In comparing the efficiency of these 

 engines, it would thus appear that neither could be said to possess advan- 

 tages over the other, as regards friction, in such a degree as to be appreciable 

 in practice, or to render the point of importance in a choice between the 

 engines ; and that if the one kind of engine had advantages over the other, 

 they must arise from other causes than difference in friction. Having taken 

 this view of the case with a supposed side lever engine, of the same length 

 of stroke and diameter of cylinder as the direct action engine, if manufac- 

 turers varied in a slight degree from this proportion, it was for the purpose 

 of obtaining a better proportion of stroke and diameter of cylinder, and con- 

 sequently a better engine than the one supposed to exist for the purpose of 

 making the observations. 



Mr. Vignoles looked upon the second propo'sition assumed by the author, 

 as being overthrown by the results of the experiments of Wood and others, 

 as to the ratio of friction to the area of rubbing surface ; and it was well 

 known practically, that the application of various unctuous substances ma- 

 terially altered the amount of the friction. A certain proportion was requi- 

 site between the area of the surface exposed to the friction and the pressure 

 upon it, to bring it within the general law. For practical purposes, he sub- 

 mitted that the law should be received with limitations. 



Mr. Gravatt said, that even allowing, for the sake of argument, that the 

 second proposition assumed by the author was incorrect, still as the paper 

 was only a theoretical examination of the comparative friction of those parts 

 of two kinds of engines, which were most subjected to strain, supposing them 

 both to be of similar power and dimensions, equally well proportioned and 

 constructed, and the same sort of lubrication of the bearings employed, he 



4 " Description of the engines on board the Gorgon and Cyclops steam 

 frigates, with remarks on the comparative advantages of long and short 

 connecting rods, and long and short stroke engines." By J. Seaward. Lon- 

 don, 1840. 



would contend that the circumstances being equal, equal results would he 

 obtained, and that the conclusions arrived at by the author should be re- 

 ceived as correct. 



Mr. Pole observed, that the objections brought forward were important, as 

 they referred principally to the fundamental laws of friction. He would first 

 give some explanation respecting the communication itself. The investi- 

 gation was commenced at the request of his late friend Mr. Samuel Seaward ; 

 it was originally intended to have especial reference to the Gorgon engine, 

 but had subsequently been extended to others. The paper, necessarily con- 

 taining much mathematical reasoning, could only be read in abstract, and 

 might, therefore, have been partially misunderstood, both as to its objects 

 and results. The object was, not to enter into a discussion of the whole 

 question of the respective merits or defects of beam and direct action engines, 

 but simply to ascertain the value of the one objection named. 



The whole friction of an engine at work with its load upon it, might be 

 divided into two distinct parts. 1st. The friction due to the engine itself, or 

 such as would be produced by the working of the engine, if unloaded. 

 2nd. The additional friction caused by the strain consequent upon the load ; 

 for it must be evident that when the engine had its work upon it, the friction 

 upon the bearings through which the strain passed, must be increased, and 

 additional friction produced, beyond that which would exist when the engine 

 was working without a load. The latter of these alone required to be cal- 

 culated, and to this mathematical analysis was more peculiarly adapted. The 

 friction of the engine unloaded, might he ascertained by the indicator, as 

 described by Mr. Field; but as he had remarked, there was no practical 

 method of finding what was the additional friction when the load was applied ; 

 indeed, it would be as difficult to find the latter by experiment as the former 

 by theory. 



He then explained the manner in which the amount of friction upon each 

 bearing had been calculated, and engines of different constructions compared 

 with each other. He had adopted precisely the plan suggested by Mr. Mur- 

 ray, namely, by taking engines of the same length of stroke and diameter of 

 cylinder, supposing them to be equally well proportioned and constructed, 

 and in equally good condition. But instead of assuming, as Mr. Murray bad 

 done, that there was somewhat more or less friction on any particular bearing, 

 his object had been to ascertain what was its actual value. If it were im- 

 possible to measure the pressures and spaces moved through, an approxi- 

 mation might be received ; but since these quantities were ascertainable, it 

 was more satisfactory to obtain results deduced from them. The conclusions 

 drawn from the paper accorded, however, with Mr. Murray's, viz. that 

 " neither construction could be said to possess advantages over the other, in 

 such a degree as to be appreciable in practice, so as to render the point of 

 importance in a choice between them." The difference between Mr. Mur- 

 ray's process and that in the paper, was, that what the former only assumed, 

 the latter endeavoured to prove. 



Mr. John Seaward's pamphlet on the Gorgon engine had been referred to. 

 The conclusions he there drew were more favourable to the direct action 

 engine, but were derived, like Mr. Murray's, merely from approximate con- 

 sideration, rather than from strict investigation. Mr. Seaward confessed, 

 that the friction caused by the strain was difficult to be calculated, and had 

 therefore contented himself with assuming, that those gudgeons through 

 which the strain passed, had three times as much friction as was due to the 

 others. He also assumed that the friction was proportional to the area of 

 the rubbing surface, a principle which no experiments had ever shown. On 

 these grounds, it was contended that Mr. Seaward's results were open to 

 objection. 



Mr. Pole then proceeded to notice the objections urged against the funda- 

 mental laws of friction which be had stated, and to give authorities for them. 

 The first of these had not been questioned since the days of Vince, by whom 

 it was proved ; it might therefore be considered as established. "With regard 

 to the second aud third, it must be noticed that they depended, in some 

 measure, upon each other, for it could be proved that if the third was true, 

 the second must be true also. The principal experiments which had been 

 made upon the friction of solids, were those by Amontons, in 1699 ; Cou- 

 lomb, in 1779; Vince, in 1784; Wood, in 1818; Rennie, in 1828; and 

 Morin, in 1831, 32, and 33. Amontons was the first who devoted any con- 

 siderable attention to the subject, and be found that friction was not aug- 

 mented by an increase of surface, but only by an increase of pressure. ' Cou- 

 lomb's researches were more elaborate, the experiments were on a large scale, 

 and were submitted to a great variety of trials ; they fully proved that the 

 friction was proportional to the pressure, and that the extent of surface did 

 not affect it." These results were further confirmed by the experiments of 

 De la Hire, Ximenes, Boistard, Rondelet, and others. Mr. George Rennie's 

 experiments were very valuable, as having been conducted on a large scale, 

 and with much care ; they were also of a comparatively recent date. The 

 results were conclusive on the point in question, for he found that when the 

 surfaces were to each other as C-22 : 1, the friction remained the same, 7 and 

 one of the general conclusions be deduced was, " that the amount of friction 

 was as the pressure directly, without regard to surface, time, or velo 

 The last and most extensive series of experiments were those by M. Morin ; 

 they were conducted at Metz, by order of the French government, and ex- 



s Vide Phil. Trans., 182'). [,. 145. 



» Mem. des Savans Strangers, 1781. Vide also Ency. Brit. New Edit., 

 Art. Mechanics. 

 i Phil. Trans. 1829, p. lot). " Ibid. p. 170. 



23 



