104 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[Aprilj 



sides, any strain on the rods would, by pressing one side of the 

 axle closer ugaiiist the hole, relieve the pressure on one half the axle 

 and increase it on the other half. 



The next point is, that the pressure of the piston cannot be fairly 

 considered conslant, as the steam is cut oft' before tiie stroke is 

 finished, that the piston may gradually come to rest at either end of 

 its path. 



It is important that it should be understood that the errors above 

 commented on are not rectified even on the assumption that the pro- 

 blem is statical and not dynamical. The class of errors first considered 

 would, indeed, be removed by tliis assumption, but the rest would 

 remain. Take one instance beside that of resolving a force at right 

 angles to its direction — tlie direction of the pressure at A would, on 

 either of the suppositions, be affected by the direction of the resist- 

 ance offered to the engine. 



We cannot help thinking that the problem which Mr. Pole has at- 

 tempted to discuss is infinitely too complicated for solution, without 

 several hypotlieses be first made to simplify tlie analysis; and these 

 hypotlieses must be the result of careful experiments. If there had 

 been even somi: resemblance to truth in Mr. Pole's investigations, those 

 who came after him might have supplied his deficiencies. As it is, 

 however, we have to regret that he has thrown away his labour, and 

 perhaps misled others. In the present discussion we think we have 

 laid down no mechanical principle which is not generally recognized 

 by mathematicians ; to them, we fear, Mr. Pole's philosophical attain- 

 ments will appear but small, though perhaps to some general readers 

 the "Silver Telford Medal" will be conclusive against us. 



H. C. 



SCAFFOLDING FOR LARGE ERECTIONS. 



" Account of iJie Scaffulding used in erecting the ' Afelson Column,' 

 Trafalgar Square." By Thomas Gwssell, Assoc. Inst. C.E — Read 

 at the Institution of Civil Engineers. 



In adopting the principle of timber scaflTolding for buildings, in pre- 

 ference to poles and ropes, Messrs. Grissell and Peto, the contractors, 

 were influenced by considerations of saving both time and expense. 

 They had long been impressed witli the want of scientific principle, 

 exhibited iu the ordinary scaffolding, and were more readily induced 

 to turn their attention to that now referred to, which they believe to 

 be an essential improvement, and calculated to be of considerable ad- 

 vantage to contractors on large works. The author is well aware of 

 the progress which has recently been made by the civil engineers and 

 architects of this country, but he ventures to claim some share of 

 merit for the practical builders, to whom is committed the execution 

 of the works designed by the engineer and the architect; and when a 

 review is taken of the stupendous public works which have been 

 executed witliin the last few years, it is evident, that without the ex- 

 ercise of great skill and the introduction of new modes of reducing 

 labour, the amount of work could not have been executed within the 

 time. 



The necessity for this reduction of labour on large works had been 

 long felt in the north, and methods had been adopted in consequence, 

 to emulate which, this timber scaffolding was introduced to London. 

 The system had been employed, in rather a rude form, by Mr. Tom- 

 kinson of Liverpool, in his quarries and stone yards, for moving stones 

 of large dimensions. Scaffulding of a somewhat similar kind was 

 used in the erection of the Arc de Triomphe, Barriere de I'Etoile, and 

 at the Eglise de la Madeleine, at Paris. 



The first time it was used by Messrs. Grissell and Peto, was for the 

 erection of the Relorm Club House (Pall Mall), under Mr. Barry, in 

 1838; then at the large graving-dock at Her Majesty's Dock -yard, 

 Woolwich, under Mr. Walker in 1839, and it is now employed very 

 extensively at the New Houses of Parliament. In these constructions 

 its general applicability was proved, and in the erection of the Nelson 

 Column (commenced in 1840}, where it was carried up to the height 

 of ISO feet, its stability at a considerable elevation was fully tested. 

 Its (usefulness is manifested, by the facilities which it affords to the 

 workmen, particularly in buildings of stone. By its aid, and with the 

 travelling machine at its summit, one mason or ' setter,' can set as 

 much work iu one day, as was formerly dune in three days ; whilst at 

 least six labourers are dispensed with, who, with the old mode of 

 scaffolding, were always required to be in attendance. It is also well 

 known, that scalfolding poles and cords are not only expensive, but 

 are subject to rapid decay, and after a few years' wear become useless; 

 in fact, the scaffulding of a moderately extensive building costs a large 

 sum when first purchased, but it is almost valueless after a compara- 

 tive short period of time. Such is not the case with the timber scaf- 

 folding, which may be said to be of no greater cost to the contractor 



than the expense of its erection, which will not exceed in any ordinary 

 case three-pence per foot cube. It is not secured together by either 

 bolts or spikes, so that the waste is trifling, and after having per- 

 formed its duty as a scaffold, it may be removed piecemeal into the 

 building, at the level of each floor and be used directly for constructing 

 the roof and the internal carpentry of the structure. The timber 

 having become seasoned by its exposure to the weather, is conse- 

 quently better fitted for immediate use. These advantages have been 

 proved in the buildings which have been mentioned, and after an ex- 

 perience of more than five years, the author strongly recommends the 

 adoption of the system. He also advises its use in moving and work- 

 ing large stones, either for permanent erectioos, or in masons' yards. 

 If used on a wharf the rent would soon be saved in labour, and by al- 

 lowing the stage to project 8 feet or 10 feet over the river, the scaf- 

 folding would be found to answer the purpose of a crane. 



The scaffolding at the Nelson column, designed by Mr. Allen under 

 w-hose direction the work was executed, is described in the Journal, 

 Vol. VI, 1843, p. 409, the annexed engraving is a perspective view. 





y^\' 



Fig. I, — ScatToldlng of the Nelson Column. 



Mr. Nicholson remarked, that a scaffolding of a similar description 

 was used in 1837 by Messrs. Cubitt, (Gray's-inn Road), for erecting 

 the entrance gateway of the London and Birmingham Railway (Euston 

 Square.) It was composed of two parallel rows of whole timber up- 

 rights, 50 feet high and 17 feet apart, surrounding the building fig. 2; 

 these were well stayed by diagonal braces, and a tram-way was foimed 

 on the top of each row, by horizontal sill pieces, bolted down and se- 

 cured by plates. The building work was executed by the aid of tra- 

 velling carriages upon the tram-ways, and when the masonry had 

 reached the height of the first scaflTold, a second series of uprights 

 and sills was added, making the total height 90 feet, which enabled 

 the work to be completed without an accident, 



