1841.1 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



32.3 



floors and curbs of such massive constructions, and for bridge constructions 

 in all their varieties. Indeed, notwithstanding the facihties with which the 

 work in the quarry is performed, the extent and depth of face exposed, and 

 the ease with which the blocks are got out of the quarry, and upon the rail- 

 ■way, it has hitherto been found difficult to supply, with sufficient rapidity, 

 the existing demand. 



The works at the Government Yard at Devonport — those of the magnili- 

 eent new graving dock now in course of construction at Woolwich — Tenby 

 Beacon in Pembrokeshire — the Neale Memorial in the New Forest, Hants — 

 and the Nelson Testimonial — the retairdng walls of Trafalgar Square — and 

 the new buildings of the Sun and Alhance Fire Otlces, in London, are all 

 supplied with granite from the Fogginfor Quarr)'. JIany private works in 

 various parts of England are also supplied with granite from this quarry, and 

 the terrace walls and their approaches in the great quadrangle of Christ 

 Church, Oxford, are about to be restored with Foggiutor granite. Indeed, 

 the fine texture and tint of Dartmoor granite adapt it peculiarly for terraces 

 and for the basements of buildings whose superstructure and other collateral 

 works are of Portland stone, Bath stone, or any of the best English free- 

 stones. 



An important feature in the quarry now under consideration is the great 

 depth at which the beds already accessible lie below the surface, yielding 

 therefrom stone of the greatest degree of compactness and strength with 

 perfect equality of colour; whilst the horizontal disposition of the rock 

 allows of the removal of stone of fair forms, and in blocks of the largest size. 

 Blocks have been sent from the quarries on Dartmoor even to Scotland to 

 supply works there with sizes which could not be procured iu that country. 

 Sir Francis Chantrey's bronze statue of King George the -tth, in Edinburgh, 

 stands on a block of Ilaytor granite, and the statue of Watt, at Glasgow, by 

 the same distinguished sculptor, is also placed on a block of granite from 

 Dartmoor. 



Mr. Rendel bore testimony to the excellence of the quality of the Dart- 

 moor granite, and to its peculiar fitness for any kind of work. The material 

 was extremely good, and of sufficient fineness to admit of the most dehcate 

 moulds being made for it. It cleaves freely ; there is little waste, and pieces 

 of stone of all sizes, from the smallest to the largest, can be readUy obtained. 

 He had, some time ago, taken the dimensions of a block, and found it to he 

 67 feet in length, 5 feet by 8 feet at one end, and 3 feet by 5 feet at the 

 other end. If a great outlay were justified, this granite would be the cheap- 

 est stone that could be used. The President stated, that he had attempted, 

 some years ago, to introduce this granite into the market by means of the 

 canal, near Tavistock, and now that such facilities existed for its transport, 

 he would direct public attention to the beautiful slabs, columns, vases, and 

 forms into which the Aberdeen granite was worked, and express his hopes 

 that before the British Association next met at Plymouth, there would be a 

 large manufactory of these articles in Dartmoor granite. The beautiful por- 

 phyry of Cornwall might also be employed in a simUar manner. He coidd 

 mention a remarkable instance of the durability of the Dartmoor granite. A 

 slab which had been used as afoot bridge from time immemorial had recently 

 been removed, and on the face, which had been turned downwards, was a 

 Eoman inscription, showing it to be at least 2000 years old. — Mr. Eaton 

 Hodgkinson, in reference to some questions which had been asked, respecting 

 the strength of stone according to the position in which it was placed, stated 

 that in all bodies of imiform texture the strength would be the same in what- 

 ever position they are ])laced, but in bodies that are laminated the case is 

 very different. He observed a veiy pernicious practice to have prevailed in 

 the construction of many of our buildings, namely, the placuig the stone 

 without any regard to the direction of its lamination. He had extended his 

 experiments to a great variety of stone, and he found that cubes of granite 

 when broken with the greatest care, break up at once into wedges. Some 

 valuable experiments on the strength of granite were published in the Trans- 

 actions of the Institution of Civil Engineers, but the mode in which the ex- 

 periments had been conducted was not stated, and a distinction is drawn be- 

 tween the crushing and the breaking force ; but he thought that if the ex- 

 periments had been made by pressing the stone between two perfectly smooth 

 plates a somewhat different result would have been found ; the granite would 

 have broken up at once without crushing, as was uniformly the case in liis 

 experiments. He thought it important to interpose a thin substance, as a 

 sheet of pa|)er, between the plate and the stone ; the pressure by this means 

 becomes more perfectly distributed. A remarkable connexion existed between 

 the ratio of the forces of extension and compression, and the angles at which 

 the wedges or masses would shde off when broken by pressure. If these 

 forces were equal, the wedges would slide at an angle of 45°. — Prof. Moseley 

 remarked that the experiments of Mr. E. Hodgkinson were peculiarly valuable, 

 because he had not confined himself to cubes, but extended his experiments 

 to other forms. A singular prejudice had existed in favour of cubes. The 

 commissioners appointed to report on the stone for building the House of 

 Commons, experimented simply on cubes, whereas rectangles would have been 

 much better. 



Dr. Lardner's Report on Railway Constants was read. Details of this paper 

 were presented to the Association in the year 1839, and reported very fully 

 in the Journal, vol. 2, page 383, but as the communication was then merelj^ 

 verbal, and the rules of the Association requure a written report, the report 

 was formally presented, and the reading led to a good deal of discussion, but 

 no new facts were eUcited. 



"Report of the Commillee on Railway Constants." By Edward Woods, 

 In a preceding Report of the Committee (published in the 8th volume of 

 the Transactions of the Britisli Association), five various modes of ascertain- 

 ing the resistance to the tractive power on railways were described, and their 

 relative merits discussed, and a variety of experiments on one of these me- 

 thods, viz , by observing the motion of a load down an incline, sufticiently 

 steep to give accelerated motion, having been made, it appeared, that the re- 

 sistance increased in a degree previously unsuspected in proportion as the 

 speed of the train increased, — but in what ratio, was not tlien determined, 

 owing to certain discrepancies due, principally, to the varying effect of the 

 wind at the time of the experiments. The Committee have continued to 

 conduct their experiments in a similar manner, repeating them with various 

 sizes of trains, at various velocities, on the Sutton incline, of 1 in 89 on the 

 Liverpool and Manchester Railway, and on the inclines of 1 in 177, 1 in 265, 

 and 1 in 330 on the Grand Junction Railway.* The data ascertained and 

 given in the Report are, — 1, The co-efficient of grarity on the inclination of 

 the plane. 2, The initial velocity of train at some determinate point on that 

 plane. 3, The terminal velocity at sotne other determinate point on the 

 same plane. 4, The time elapsed in traversing the space intervening betweeu 

 these two points. 5, The space intervening. 6, The force of gravitation. 

 7, The weight or mass of the train, exclusive of the wheels and axles. 8, 

 The weight or mass of the train subject to the rolling motion, viz., the wheels 

 and axles. 9, The radius of the wheels. 10, The distance from the centre 

 of the wheel, to the centre of oscillation. If a body move down an inchned 

 I)lane without resistance, its velocity at any given depth below the level of 

 the point where its motion first commences, will be equal to the velocity it 

 would have acquired by a free vertical descent through the same height. This 

 standard velocity being compared with the observed velocity of a body mov- 

 ing down an inc'hne, and meeting with resistance, the amount of tliat resist- 

 ance can be assigned. This mode has been objected to, from the apparent 

 inconsistencies iu the results ; but these may be readily explained ; and the 

 Report shows a remarkable correspondence in the motions of the same train, 

 when permitted to descend the same plane from the same point, provided the 

 atmosphere be perfectly calm. The usual formula is applicable to three cases 

 of accelerated, uniform, and retarded motion ; the co-efficieut of gravity is 

 greater than, equal to, and less than the co-efficient of resistance accordingly ; 

 and the requisite correction will be negative, zero, and positive, so that the 

 co-efflcient of resistance tnay be found in all cases. The method of determin- 

 ing this correction was set forth in the former Report. When the motion is 

 uniform, the mean resistance for any particular velocity may be assigned; but 

 when the motion is accelerated or retarded between the two points of obser- 

 vation, although the mean resistance may be known, it cannot be stated with 

 accuracv, whether that mean resistance is due to the mean velocity, or to 

 some other velocity intermediate between the Umits of the initial and termi- 

 nal velocities, because experience has not yet assigned the law of the corres- 

 ponding increments of resistance and speed. The results which the tables of 

 this Report present, are considered under the following heads : the determi- 

 nation of the friction ; the additional resistance produced by increase of speed 

 in trains of different sizes ; the effect of modifying the form of the front or 

 end of carriages, and of other changes in the external surface of the train. 

 Three first-class carriages were allowed to descend the Sutton incUne from 

 rest four times in succession, a length of 2420 yards. It appears that the 

 resistance diminishes until the train attains the speed of 7-58 miles per hour, 

 after which it increases; at 4-32 miles per hour, the resistance was 6-07 IU. 

 per ton ; at 7-58 miles per hour, 5-6 tb. per ton. This remarkable and hitherto 

 unobserved result is owing, probablv, to the more perfect lubrication of the 

 axles at the higher speed ; a certain thickness or film of grease is formed be- 

 tween the bras's step and the upper surface of the journal, and keeps the two 

 surfaces more effectually apart ; at the lower velocities, the pressure of the 

 step upon the journal has a longer time to act in effecting the displacement 

 of the fresh grease which has been suppUed from the box, and the result is, 

 a greater amount of friction. Eight second-class carriages were allowed to 

 descend the Sutton incline ; the friction was a minimum at o-84 miles per 

 hour. The following results mav be deduced from the above-mentioned 

 series of experiments. 1, The friction was least when the train was moving 

 at the rate of about 6 miles per hour. 2, The total resistance was also least 

 at the rate of about 6 miles per hour, notwithstanding the effect of the atmo- 

 sphere .It that speed. 3, The mean resistance of first-class caiTiag_es was 

 never less than 5-6 ft), per ton ; aud of the second-class never less thaii / -/S lb. 

 per ton ; 6 and 8 ft. per ton will represent very neariy the mean of the resis- 

 tances ; and these values are used in the subsequent part of the Report, ine 

 motion of these trains being observed at lower parts of the inchne, where the 

 velocities were greater than the preceding, the resistance to the train of three 

 carriages was 8, 12, aud 16 ft. per ton, at velocities of 22, 26, and 29, miles 

 per hour respectivelv, and the resistance to the train of eight carnages was 

 11, 12, and 14 J ft. per ton, at the velocities of 20, 25, and 29 nnles per hour. 

 Trains of 4 and of 6 carriages were impelled to the summit of the 'nchne, 

 and, the engine being detached, commenced their descent at the rate of 33 

 and 26 miles per hour. They descended through the first half of the 'nc me 

 with a mean velocitv of 34 and 29 miles per hour, and through the latter 

 half, with a mean velocity of 37 and 33 miles per hour. Other series of ex- 



- As Dr. Lardner's paper on " the Resistance of Air to Railway Trains/' 

 (read at Newcastle, and reported fully, with fa-rams Juurnal vol 2, p. 

 383, was founded on these experiments, the reader had better retei to it. 



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