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THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[May, 



tended over a period of three years (1831, 1832, and 1833), no expense or 

 trouble having been spared to render them conclusive and satisfactory. ,J The 

 results were given by Professor Moseley, in his new work on the mechanical 

 principles of engineering. , „ They proved that "the friction of any two sur- 

 faces was directly proportioned to the force with which they were pressed 

 perpendicularly together,," and that " the amount of friction was, in even- 

 case, wholly independent of the extent of the surfaces of contact." 1 ' The 

 before mentioned experiments all agreed, that the friction was proportional 

 to the pressure, and was independent of the extent of surface. In opposition, 

 however, to these, stood the experiments of Professor Vince, of Cambridge, 12 

 which led him to the conclusion that the friction increased in a less ratio 

 than the pressure, and that it was not altogether independent of the area of 

 surface. These experiments were probably conducted with care and accu- 

 racy j but it was also probable that equal precision had been used in those 

 which proved the contrary ; and if this was allowed, the majority of coincid- 

 ing experiments might, as in all other cases, be safely received in preference 

 to one dissentient. But if the particulars of Professor Vince's experiments 

 were examined, many circumstances appeared which would render them less 

 worthy of regard than others. It was not shown that he experimented upon 

 metals, but that he used pieces of wood, either hare or covered with paper, 

 and the experiments were on a small scale, the moving bodies being at the 

 utmost a few ounces weight ; while Coulomb, Renuie, and Morin, had ex- 

 tended their trials to all kinds of materials, and had used considerable 

 weights. Professor Vince himself, although satisfied with the method of 

 conducting his experiments, did not seem equally so with their results, as 

 regarded the influence of surface and pressure, for he had remarked, " that 

 no general rule could be established to determine it, even for the same 

 hody." 



Quotations were then given from Gregory, Brewster, and others, corrobo- 

 rating this view of the inconclusive and unsatisfactory nature of Vince's ex- 

 periments. The law of the influence of pressure and surface upon friction, 

 was occasionally modified by accidental circumstance:,, two of which might 

 be noticed, as they had been expressly treated of by Rennie and Morin. 



1. It was only applicable within the limit of pressure which would not 

 injure and abrade the surfaces ; for when heating and undue attrition com- 

 menced, it was natural that the law would not hold good. Well-constructed 

 machinery, however, was never supposed to pass this limit, and therefore this 

 cause of irregularity might be rejected in calculation. 



2. Another modification was produced by the application of unguents; this 

 was treated of by Mr. Wood, 11 whose experiments showed that when un- 

 guents were introduced, there was a certain area of bearing surface, propor- 

 tioned to the weight, which was peculiarly favourable as regarded the loss by 

 friction, but that when this area was preserved, the friction was in strict ratio 

 to the pressure. 



It could not, however, have been Mr. Wood's intention, from these results, 

 to impugn the applicability of the established general laws to the purposes of 

 calculation, hut only to show the existence of modilying circumstances under 

 certain conditions; for the formula he had given 14 assumed the friction to 

 be as the weight, and had no element in it expressing the area. 



Mr. Rennie and M. Morin had also examined the influence of the an- 

 guento, and had found that their introduction did not materially alter the 

 general laws of friction, but only affected the value of the co-efficient or 

 multiplier to be used in ascertaining its numerical amount. 



Having thus brought before the meeting the result of the principal experi- 

 ments on friction, Mr. Pole concluded by adducing the testimony of writers 

 on mechanics, who guided by these results, had promulgated the laws deduced 

 from them. He gave quotations from the following authors in corroboration 

 of his \iews, viz. — Emerson, 1 "' Playfair, 10 Trcdgold, 1 ? Barlow, 1 8 Larduer. 11 ' 

 Farey, 20 De Pambour, 21 Poisson.--' Pratt, 8 ' Whewell, 9 * And Mosi 

 With the last mentioned author Mr. Pole bad taken an opportunity of con- 

 versing upon the points in question, and the principles adopted in the paper 

 had received the Professor's full approbation as corresponding with those 

 made use of in his own treatises. 



Mr. Vignoles thought that great praise was due to Mr. Pole, for the re- 

 search and mathematical reading exhibited in treating the questicn of com- 

 parative friction. In the former remarks he had made, it was not his inten- 

 tion to impugn the accuracy of the abstract proposition, " that friction was 

 independent of tlie area of bearing surface," any further than to qualify it in 

 its practical application, with the proviso, " that proper proportions were 

 maintained between the area and the pressure, according to the description 

 of mechanism, subjected to friction." He therefore desired to consider the 



" Mem. de l'lnstitut., 1833. 1834, and 1838. 



10 The Mechanical Principles of Engineering and Architecture. By the 

 Rev. H. Museley. M.A. 8yo. Longman and Co. 1843. 



' ' Ibid. pp. 138. 139. ' -' Phil. Trans., 1785. p. 16.1. 



1 ■■ Treatise on ELailn ads. 3rd Edit. p. 396. et seq. ' " Ibid., p. 355. 



' ■■ Mechanics, 1760. Prop. 62. 10 Outlines of Nat. Phil.. 1834. Art. 159. 

 17 Treatise on Railroads. 1825, p. 46. 1B Math. Diet.. Ait Friction. 



19 Library of Useful Knowledge, Mechanics, 3rd Treatise, Art. 7. 



20 Treatise on the Steam Engine. 1 1-27. p. 60. 



-' Treatise on Locomotive Engines, ISiO, chap. viii. 

 "Trailede Mecanique, 183:;. Art. 156. 

 23 Mechanical Philosophy, 1836, Art. 118. 

 2 * The Mechanics of Engineering, 1841, Art 101. 



25 Mechanical Principles of Engineering, 1S43, Art. 133, and Part 3rd, 

 passim. 



question, as to how far iu practice one kind of engiae varied from the other 

 in the general amount of friction, and to examine how far the areas of the 

 bearing surfaces, were in proportion to the insistent weight, caused either by 

 the strain of any angle or by the direct weight on any of the journals of the 

 moving parts ; this inquiry should precede the abstract mathematical inves- 

 tigation. The friction of different substances would not follow the mathe- 

 matical rule, unless the due proportion between area and pressure was ascer- 

 tained and observed ; these proportions would be very different in heavy ma- 

 chinery, such as marine steam-engines, and the axles of railway carriages. 

 With these qualifications he aereed with the general propositions laid down 

 by Mr. Pole. 



Mr. Murray agreed with Professor Vignoles in thinking that the extent of 

 surface in machines materially affected iu practice the amount of the friction. 

 He did not mean to advocate the correctness of Professor Vince's experi- 

 ments, but he would draw attention to the results quoted by Dr. Gregory, 26 

 in which the difference of Vince's experiments and those of other writers on 

 the subject, was attributed to their not taking into account the cohesion of 

 the bodies experimented upon. Their experiments were made with inclined 

 planes, which were raised until the bodies began to move, and the amount 

 of friction was then deduced from the angle of inclination that had been 

 given to the plane : from this mode it was contended that no definite laws 

 could be laid down. Mr. Murray acknowledged that on dry surfaces, 

 within certain limits, the amount of friction was not influenced by the extent 

 of surface ; but he contended that in practice, as different kinds of unguents 

 were used, the cohesion arising from the impurity and clamminess of these 

 lubricating substances, must be considered and allowed for. 



Major-General Pasley said that when he was quartered at Malta, he tried 

 some experiments on friction, by having a slab of .Maltese stone, which re- 

 sembled the oolite of Bath, rubbed smooth and placed horizontally ; other 

 pieces of smooth-faced stone of the same quality, but of different areas, were 

 then attached to a cord which was weighted and passed over a pulley ; the 

 weights which were just sufficient to give motion to the several pieces of 

 stone, were then noted, and it was found that the area of the surface was 

 not important, the friction being directly in proportion to the insistent weight 

 of the stone. He could therefore corroborate Mr. Pole's propositions. 



Mr. Farey considered that Mr. Pole had treated the subject of friction so 

 well, and bad selected his authorities in such a manner as to establish his 

 position incontroverted) ; be would therefore only remark, that iu collating 

 the friction experiments for his work from Dr. Gregory and others, he had 

 in a measure rejected those of Vince, as being on too small a scale, and not 

 of sufficient importance to rely upon as authority. It must be admitted, that 

 viewing the question practically, there were circumstances which would in- 

 fluence the proposition. If the surface of a journal was so small as to drive 

 out the unguent, or to cut into the lower bearing, the friction would be 

 unduly increased, and the theoretical position would no longer hold good. 

 The use of unguents would not interfere with the general proposition, 

 although in practice, any substance used for lubrication, which, when cold, 

 solidified and became adhesive, might, for a time, produce an increase of 

 friction ; this of course would be avoided, but it would not bear upon the 

 general question. 



Mr. Rennie corroborated the position assumed by Mr. Pole, "that friction 

 wa- independent of the extent of the rubbing surface;" his experiments, 

 which had been tried on a large scale, and with various substances, gave uni- 

 formly this result, within the limits of abrasion ; when that commenced, the 

 bearings heated and there was an end of the theoretical position. The 

 texture also, of the rubbing surfaces altered the condition ; for instance, any 

 light body covered with cloth opposed a considerable resistance by the friction 

 of the raised nap ; but if the body was weighted, it again came within the 

 limits of the law. became it more nearly resembled hard substances, which 

 alone were considered in theory. Hard and soft woods varied, of course, in 

 the same manner. The friction upon each other of metals of different degree 

 of hardness, caused in practice, some little variation, but it was so slight, 

 that the rule quoted, might be safely received as correct. 



Mr. Davison stated that he some time ago made several practical experi. 

 ments with an Indicator, constructed by Messrs. Maudslavs and Field, for the 

 purpose of ascertaining the power required to drive various kinds of ma- 

 chinery, in Messrs. Truman, Hanbury, Buxton, and ( o's Brewery. 



1st. lie found, that an engine which indicated 50 horses power when fully 

 loaded, showed, after the load and the whole of the machinery were thrown 

 off, 5 horses, or one-tenth of the whole power. 



2nd. 190 feet of horizontal, and 180 feet of upright shafting, with 34 

 bearings, whose superficial area was 3300 square inches, together with 1 1 

 pair of spur and bevel wheels, varying from 2 feet to 9 feet in diameter, 

 required a power equal to 765 horses. 



3rd. A set of three-throw pumps, C inches in diameter, pumping 120 bar- 

 rels per hour, to a height of 165 feet, = 4'7 horses. 



By the usual mode of calculation, (viz., 33,000 lbs. lifted one foot high 

 per minute,) it would appear that there was, in this case, friction to the extent 

 of 13 per cent. 



4th. A similar set of three-throw pumps, inches in diameter, pumping 

 160 barrels per hour, to a height of 140 feet, = 6 2 horses. 



By the same mode of calculation as before, there was here, friction to the 

 amount of 15 per cent. 



• Gregory's Mechanics, vol. li. p. 25. 



