Page:The Building News and Engineering Journal, Volume 22, 1872.djvu/189

 Marca 1, 1872. THE BUILDING NEWS. 173 of their form. Mr. Parker believed that the shaft with pilaster was made more important in order to carry an arch spanning the nave, as in the abbey church of Lensig, near Bayeux, thus serving the purpose of a truss, the intermediate shaft carrying a secondary truss. He did not explain, however, how that intermediate shaft was coupled to the cen- tral column of the four arches above mentioned. M. Ruprich Robert pointed out that the absence of any external buttress to the clerestory of the Abbaye aux Hommes was a sufficient reason that there should be no arch inside, and that the buttresses of Lensig, its later date than that supposed, and other differences in the arrangement of the arcades, pre- eluded the possibility of its being taken as a prece- dent for the Abbaye aux Hommes. He believed that the difference in the vaulting shaft was due to the fact of its having been originally intended to have a principal and secondary truss only, and no arch, and assumed that the two central arcades were an after-thought, there being only two projected at first—viz., those in front of the windows. M. Bouet, Mr. Spiers believed, originated Mr. Parker’s opinion as regards the arch spanning the nave. He seemed, however, in his book on the Abbaye aux Hommes (p. 35), to lean towards the opinion that it was intended from the beginning to vault over the nave with quadripartite vaults, taking in two bays each. And he pointed out, in support of this, the means taken to counterbalance the thrust of his nave vault by the conjunction of the inner and outer wall of the clerestory with solid masonry on each side of the main ribs, and the isolation of the four arcades in the centre of each double bay, whilst at Lensig the arcades fill up the whole width. This, however, did not explain the use of the intermediate vaulting shaft except as an esthetic necessity, Be- tween these various opinions, said Mr. Spiers, it was difficult to draw any line. He believed, how- ever, that, on the whole, M. Ruprich Robert was right, and that M. Bouet’s suggestion of the arch was not tenable. This became the more evident on an examination of the elevations of the original elerestory walls as restored in M. Bouet’s and M. Ruprich Robert’s works, for in both of them the pilaster and shaft were carried up to the level of the springing of the four arcades, far above, therefore, any possible springing of an arch spanning the nave. Mr. Parker himself allowed ‘that the difference in the size and form of the alternate piers is, taken by itself, no positive proof that there were original tranverse arches of stone to carry the roof, as at Lensig; the same arrangement occurs at Winchester and at Waltham, which were not vaulted, and had no transverse arches, so that they must have been used for carrying the principal timbers only.” On the other hand, were it not for the continuation of the pilaster and shaft before mentioned, the great strength of the original walls behind the main trans- verse ribs might be taken as an argument in favour of the transverse arch. Altogether, it was a difficult nut to crack. The subject, however, was probably of sufficient interest to justify his (Mr. Spiers’s) translation of certain descriptions in M. Bouet’s work, especially as the publication of it in 1868 was posterior to the treatment of the subject by Mr. Parker in his two papers read before the Royal Institute of British Architects. M. Bouet, after de- scribing the transept, where no vault was originally intended, remarked (p. 35), ‘If, as we have seen, the clerestory of the transept is irreconcileable with any kind of vault, it is not the same with the nave clerestory. The plan itself seemed to show some hope of attaining this end, so that when in later times was built the vault which we see now, there was no necessity, as in the transept, to build in to the old walls shafts to carry it. Further, we notice that whilst the intermediate pier is so weak in its construction as to justify the belief that it played only an unimportant part, the inner and outer-wall of the clerestory above the main piers are built between and form a solid mass, a real internal buttress cap- able of resisting a considerable thrust, an arrange- ment which seems to us little in accord with a trussed rafter roof. Whilst at Lensig the arcading fills in all the bay, at the Abbaye aux Hommes, by suppressing the two side arches, they reserved to themselves, at least for the future, the possibility of building a quadripartite vault, square on plan. Did they shrink from the difficulty, or were they unsuc- cessful in their first attempt? We are left in doubt.” In the next page he gave a restoration of the plan of the old clerestory, and inserted a shaft (which would be the continuation of the intermediate shaft) coupled to the central column of the arcade, but he gave no explanation of its use, and did not show it in section. Further on he said, ‘‘We do not know what becomes of the shafts and pilasters which now carry the nave vault. They become lost in the vault at the level of the great capitals on which the ribs are supported, and we find no trace of them except at the level of the impost moulding of the four arcades, where a broken block of stone with a kind of abacus would lead us to suppose they ter- minated with a capital whose function was, perhaps, to carry the struts supporting the tie-beam.” It was very evident from these quotations that although M. Bouet may have originated the idea on a trans- verse arch, and in 1863 may have, according to Mr. Parker, been brought to agree with it, he must haye again changed his mind, for no allusion was made to the idea in his book published in 1868. With all this, however, the intermediate shaft was still a matter of perplexity, for he (Mr. Spiers) doubted whether a hexapartite vault was even dreamt of in the eleventh century. He could only, therefore, throw out as a suggestion the esthetic necessity for such a shaft to divide the double bays of the nave and produce that repetition of vertical line which tended to increase the apparent length of the in- teriors of our cathedrals and abbey churches. Hav- ing described and compared at great length the salient features of the two abbeys of Caen, Mr. Spiers brought to a conclusion a most interesting paper, which was copiously illustrated by drawings and plans. In the discussion which followed, Messrs. G. R, Redgrave, L. W. Ridge, H. C. Boyes, S. F. Clarkson, and others took part, and the usual vote of thanks having been passed to Mr. Spiers for his paper, that gentleman replied to some of the points raised, and the proceedings terminated. ——__@—_____ PARISIAN STEAM ROAD ROLLING. lias following is an extract from a lengthy statement by Messrs. Gellerat & Co., the parties most actively identified with the use of the steam road roller in Paris :— “As long ago as 1860, experiments in road rolling by steam-engines were made in Paris. These experiments, again taken up in 1864, and continued by Messrs. Gellerat & Co., induced, in consequence of comparative trials between the horse road rolling and steam road rolling, the engineers employed by the Paris municipality to conelude, in 1865, a con- tract with the company. ‘This has given both ex- tension and a regular and permanent character to the application of this process. The contract, made for six years, obliges the company to keep perma- nently at the disposal of the city of Paris seven steam road rollers of the construction patented by them. ‘These rollers are principally intended for rolling the macadamised roads of Paris and of the the Bois de Bologne and Bois de Vincennes; but they can also be used for setting paving stones and for rolling the foundations of paved roads. The contract fixes the maximum and minimum diameters of the two carrying rollers of each engine, the maxi- mum width of the machine, the speed of travel of the engines, and the weight per metre run of the width of the external diameter of the carrying rollers. The work done is paid in the compound ratios of the distance traversed by the engine at work on broken stone to be rolled, and of the weight of the engine itself. The unit of the accounts is the kilo- metric tonne—that is to say, 1,000 kilogrammes of the weight of the engine carried a distance of 1,000 metres. This unit is paid for at the rate of 0:50 francs during the night and 0:45 francs during the day. As regards the average weight of the engines, it is determined by weighing, checked by both parties to the contract, and the distance passed over is given by a counter driven off the rollers, The distinctive qualities of the rolling engines employed in Paris are:—The entire utilisation, for the progression of the machine, of its weight; and the identity of the front and hind parts of the engine —an identity which allows it to work with the same ease in both directions, and, consequently to advance in either direction without turning round. The two carrying rollers are both drivers, and are propelled in the same way, butseparately, by the steam-engine. We have to add that the engines can turn in a mini- mum radius of from 10 to 15 metres—82ft. to 48ft. —according to their dimensions. Thus, with their power of going either backwards or forwards, this allows them to work in the most narrow streets and to pass the sharpest corners. The application of the whole weight for obtaining adhesion gives the Gelle- rat Company’s engine great traction power—a power often entirely called into play, especially when the metalling is of bad quality and the foundation of a yielding nature. A steam road roller without this power would often be incapable of moving itself on freshly laid metalling, and, ¢ fortiort, of dragging itself out of the many difficult positions to be en- countered in making new roads, The average weights of the Gellerat engines, in the order in which they are used, are 17, 24, and 30 tonnes of 1,000 kilo- grammes—in English weights, 16 tons 14ewt. 2°dqr. ; 25 tons 12ewt. 1°6qr., and 29 tons 10 ewt. 2-094qr. respectively. The weights per metre run of the rollers are 6,000 kilogrammes for the smallest engines, and 8,000 kilogrammes for the two other sizes. Engines of these graduated sizes have been able to execute all the work which has offered itself up to this day. The lighter engines are more particu- larly suited for new work under difficult conditions ; the heavier rollers, which can also be used on new work, are more suited for maintaining roads, They can rollin a single night a very considerable road surface. The maximum speed with which the en- gines are to work has been fixed at 4 kilometres, or 2 miles 854°5 yards per hour. This speed, but seldom attained, is still less commonly exceeded, We may estimate, as a general rule, the speed of 3 kilometres, or 1 mile 1,520 yards per hour, as the average velocity developed from the beginning to the end of an ordinary day’s work. Rather less at the begin- ning when the draught is considerable, it increases with the degree the binding of the road approaches com- pletion. Since 1866 there has been steam-rolled in Paris a total volume of 32,000 cubic metres, or 41,857 cubic yards of metalling of different kinds, such as flints, gravel, broken stones, more or less hard mill- stone grit, porphyry, and trap—the last a metamor- phic quartz rock. These different materials are all rolled in the same way, with slight differences de- pending on the manner they behave under the action of the rollers, Pebbles and gravel, which at the outset are very movable under the rollers, form a wave in its front. A small quantity of water is sometimes sufficient to diminish this tendency ; pebbles bind easily with the addition of sand. These last materials are cheaper than those generally used in Paris, but they are much employed for keeping up roads subjected to considerable traffic. Millstone grit, still more binding than the preceding materials, is easily rolled, and affords an easy draught and ready maintenance. Porphyry and trap, being much harder, require to be longer rolled. The crushing together of the materials is slower, and the binding more difficult; but when this double result is obtained, the road offers a considerable resistance. On these ma- terials the heavier engines are particularly efficacious. The working of the engine remains to be spoken of. Weare here confronted by a rule which is never departed from, whether as regards a road being rolled along its whole breadth, or only half its breadth, though it principally relates to the case in which the whole width is being rolled. The opera- tion is always begun at the sides. The roller at first executes a certain number of passages over one of the edges of the macadam. When the stones begin to be brought together the surface is slightly watered from a barrel or by a jet, and by means of a spade a very thin layer of the sand provided is spread. At each passage the roller is gradually brought nearer ta the crown of the road. The operation is continued in this way for some time, and when the one side of the road is sufficiently bound, the other is begun with, and brought to the same state as the first. The central part is done last and in the same mode. The roller thus passes over the whole surface, staying longer over those portions less squeezed together than the others. During the operation the road is moderately sanded and watered. As we have said, towards the end the excess of water runs to the surface, taking with it also any excess of binding material. The rollers then produce no impression. By this means a smooth hard road is obtained, and it can be at once open to traffic. The heaviest carts leave no trace.” SEER ane TESTING STEEL BY THE MICROSCOPE. OHN SCHOTT, an eminent chemist, asserts that different qualities of iron and steel can readily be distinguished by means of the microscope. The crystals of iron are double pyramids, in which the proportion of the axes to the bases varies with the quality. The smallness of the crystalsand the height of the pyramids composing each element are in pro- portion to the quality and density of the metal, and these are to be detected also in the fineness of the surface. As carbon diminishes in steel, the pyra- mids have less height. In pig iron and the lower qualities of hard steel, the crystals approach more closely the cubic form. Forged iron has its pyramids flattened and re- duced to superposed parallel leaves, whose structure constitutes what is called the nerve of the steel. The best quality of steel has all its erystals disposed in parallel lines, each crystal filling the interstices between the angles of those adjoining. These crystals have their axes in the direction of the per- cussion they undergo in the working. Practically good steel, examined under the microscope, has the appearance of large groups of beautiful crystals, similar to points of needles, all parallel.