Page:The Building News and Engineering Journal, Volume 22, 1872.djvu/455

 May 31, 1872. THE BUILDING NEWS. 433 his art handwriting in material visible to all | OUR PRESENT KNOWLEDGE OF BUILDING who can read such writing, and who have an eye for it. If Mr. Corbie, or any one else, even Viollet le Duc, will but study carefully any such wnrestored remains of the genuine old work, either here or on the Continent, he will need no records or documents of any sort, but the noble and bond jide work itself! All the interest of the great and precious work of the past lies in this, and any interest which will in the future attach it- self to architecture must lie in it also. There is no other way. It does not much matter what name a man goes by, whether architect or clerk of the works: architect of the works we think a good and _ sufficiently descriptive term; but the point really is, what does he do, and how does he do it, and how much of the personal and individual is there in it? Like a picture, is it his—his own thought, and his own manual work, as far as that term is to be understood of the drawings and directions necessary to guide the executive workman ? It would be a curious thing to calculate how long it would take any one man, a practised draughtsman, to make all the drawings necessary for the practical carrying out of the apse or altar end, not in- cluding the chapels, of Westminster Abbey, columns, arches, windows, clerestory, and roof, with full-sized details drawn as the work went on. ‘They all harmonise and come together, making a perfect whole. How long did it take to do it all—not the work itself, but the indicative drawings? It is like a picture—all is unity ; and like a picture, it must have been the work of one hand and thought, but the hand of the thinker must have worked out the thought. It could not have been produced by mere “‘ organisation,” or a ‘ staff,” however efficient. To have produced the Athenian Parthenon, or the Gothic Westminster, or Chartres, by any process of manufacture, would have been an impossibility. In the present day, a man may well superintend twelve or fifteen cathedrals, and ten times twelve churches ; but he cannot by any human possibility design and work them all out in elaborate detail, artistically! No man can doall things. We would, therefore, look on these utterances of the Quarterly as but the first expression, im- perfect as it may be, of a coming appreciation of a true artistic action, and of hope and promise to the artists of the future. It is not anew thought, or new thoughts, except to those many who pay but little attention to the means whereby art is produced. It has long been advocated in this journal that art cannot be manufactured, that art is the expression of the mind and hand—we repeat it—the hand of the artist. Itis, there- fore, not a little hopeful that the thought has been taken up in other and such influential quarters, and it is no less hopeful that Mr. Gladstone himself, who has been an art student, as he tells us, all his life, should have thought it not amiss to comment on it at the Royal Academy. That he was offended at the idea foreshadowed seems not a little strange, for not only has he recognised the value of the individuality of art action, but he has specially dwelt on it in his well-known book on ‘‘ Homer,” wherein the famous shield of Achilles is described at great length, and enthusiastically praised as a specimen of artistic power, not only of inventive faculty, but of wondrous power of hand. We would refer to Homer, and cite him as an authority in our fayour, and contend that Homer lived, happily for him, at a time when art and architecture, in their bond fide sense, rude though they might be, were human necessities, and that the very absence of machinery, as a dominant power and could not exist. Are we in advance in art, and mode of producing it, of the rude men in old Homer’s day, or were they more artistic than weare? Let any art studentlook at the antique Greek for an answer and say. Ca B.2A2 MATERIALS, AND HOW TO IMPROVE IT. ees was the title of a paper read by Captain Seddon, R.E., at a meeting of the Royal Institute of British Architects on the 22nd April. The question raised in the paper was whether architects and engineers are yet sufficiently ac- quairted with the properties and strength of the different materials in common use to enable them to employ such materials to the best advantage, or to allow of their calculating with accuracy the amount of material necessary in every part of a structure to meet the different stresses called into play. It might be asked, ‘‘ What more information do we want than that already within our reach?” There are hand- books enough, in all conscience, with copious tables, giving the strength of all kinds of materials under every description of stress, and formule for calcu- lating the requisite dimensions of beams, columns, &ce., of different forms and under varied conditions. Nevertheless, it must be admitted, on a little re- flection, that the present state of knowledge on these matters is, in face of the boasted enlightenment of the nineteenth century, by no means so satisfactory as at first sight may be imagined, nor in any way sufficient to warrant contentment without making further researches. Most of the data upon which calculations have hitherto been based have been derived from experiments made on picked specimens, too small in size, and too free from such ordinary defects as are sure to occur in larger specimens, to give very reliable grounds to go upon, the result being that defective knowledge has to be supple- mented by using large factors of safety, or, in other words, by not straining the material used to any- thing like its estimated powers of resistance. True, it might be argued, on the other hand, that any slight defect would weaken a small section more than a larger one, and, therefore, that the great difference of strength attributed to the careful select- ing of specimens might, in a great measure, be counterbalanced by the certainty of there being some slight defects even in the most carefully selected specimens; but in this case we were only dealing with probabilities, and not with ascertained facts. Again, the results obtained from different experiments made by Muschenbrock, Rondelet, Rennie, Barlow, Hodgkinson, Fairbairn, and others, varied so considerably that little or no reliance could, in many instances, be placed upon them; nor were these discrepancies difficult to account for when it was considered that the experiments were made by many different hands, with different degrees of care, on a comparatively limited number of specimens, and that the means employed for carrying out the experiments differed in almost every instance, being often of such a kind as to be incapable of recording any accurate results. A glance at some of the dis- cordant results obtained would show how much value ought to be attached to them. TIMBER, Taking the subject of timber first, Captain Seddon said he could not, perhaps, do better than quote from a valuable little treatise lately published by Mr. B. Baker, C.E., ‘“‘ On the Strength of Beams, Columns, and Arches.” At p. 127 he says :—‘ Un- fortunately, most of the careful experiments of Tredgold, Barlow, and other early investigators, were made on small pieces of timber, straight grained, and free from knots and other defects; a condition favourable, it is true, to the comparison of the results of mathematical investigation with those derived from direct experiment; but, on the other hand, leading to errors of much greater moment in actual practice, since (as every workman knows) a piece of timber uniformly sound through- out can never be reckoned upon.” He then goes on to show the percentage of loss of strength due to the inevitable defects in large scantlings, as follows :— A piece of English oak 2in. and lin. square gave a result equivalent toa breaking weight of 8} ewt. applied at the centre of a lin. square bar supported on bearings 12in. apart, giving a calculated stress on the extreme fibres of the bar equal to 7-6 tons, or 17,024lb. per square inch, a surprisingly high, and as far as practical cases are concerned, a_pal- pably-exaggerated result. Whereas, taking a larger scantling of oak, 11ft. 9in. long and 8}in. square, the calculated stress on the extreme fibres, when rupture took place, was only 5 tons, or 11,200Ib., instead of 17,000lb., per square inch; and a larger beam still, 24ft. 6in. long, 124in. deep, and 103in. wide, gave a result equivalent to less than one-third of that given by the small selected piece. Tie then says:—‘‘ This reduced amount shows that the average strength of the timber in this large beam was less than one-third of that in the small selected piece; and we think no further illustration is re- quired io show the necessity of neglecting the ma- jority of experiments made on small scantlings of oak when deducing rules for practical application. We find the same conclusions hold good with reference to Riga, Memel, pitch pine, and other soft woods,” the standard bar 12in. by lin. square giving a maximum stress on the fibres of 3} to 4} tons per square inch, whilst experiments on a beam 1dft. long and 12in. square give a maximum stress of only 24 tons per square inch. If we turn to Moles- worth’s ‘‘ Handbook of Engineering Formule,” ard Hurst’s ‘Architectural Surveyors’ Handbook,” both of which are books purporting to supply all thela‘est information brought up to date each year, we find the value of the constant to be applied in the formula for beams under transverse stress given as 5 for English oak, 5 cwt. being taken as the central load required to fracture a standard bar 12in. long and lin. square, although the tensile strength of oak in pounds, in Molesworth’s ‘* Handbook,” is given as 17,000Ib., which would give 8} ewt. instead of 5 ewt. as the central breaking load, Professor Rankine, in his “‘Rules and Tables,” gives 10,000Ib. to 19,0001b. per square inch as the tensile strength of oak, and 12,0001b. to 14,0001b. for fir or pine. Glancing at the crushing strength of timber, as given by different experimenters, it would be found that Rondelet gives the crushing strength of pine as from 54 ewt. to 62 ewt. per square inch, and that of oak as 45 ewt. to 54 ewt. Tredgold took36 ewt. for both. Rennie gives the strength of pine at 14 ewt., and of elm as lowas 11} cwt. per square inch. Hodgkinson gives 92 ewt. for elm, 90 ewt. for oak, and about 54 ewt. for pine. Lastly, the author gave the results of some experiments made by Mr. Kirkaldy on two logs 20ft. long and about 13in. square, one of white Riga and the other of red Dantzie fir, which show, in the first case, a resistance to crushing of 17-5 ewt., and in the last of 15°5 ewt. per square inch. Both balks failed by crushing, the lateral deflection not exceeding *64 of an inch in either case. These results approximate closer to those obtained by Rennie than any of the others. Here is a mass of conflicting evidence, notwithstand- ing the apparent simplicity of the subject ; and yet it is by no means as simple as it seems. The condi- tions were no doubt very different in each set of experiments ; the apparatus employed was different ; there were different observers, and therefore it is not to be wondered at that the results arrived at differ. In fact, the seasoning alone of the specimens would at once account for a great part of the difference, for green timber, from the moisture in it reducing the lateral adhesion of the fibres, has not more than half the strength of dry timber; and yet, if arti- ficially over-dried, a considerable loss of strength would be the result. With regard to the transverse strength of timber beams especially —though the same remarks apply to those of iron or any other mate- rial—what would appear to be an important element in their strength, though hitherto omitted from all calculations, is the lateral adhesion of the fibres to each other. It is evident that, as the extension of the fibres varies according to their distance from the neutral axis of the beam, as the beam bends, the fibres, if free to move, would slide upon each other, which sliding is resisted by the adhesion of the fibres to one another, thereby increasing the resistance of the beam both to deflection and breaking. For instance, if a beam is supported at each end and loaded, it will assume the form shown in Fig. A. If, however, it were conceived to be made up of a number of thin layers, it would assume the form shown in Fig. B., the difference being due to the resistance of the fibres to horizontal shearing, in addition to their resistance to direct tension and compression. ‘The means of measuring this force is given by Rankine at p. 88 of his ‘ Applied Mechanies.” Mr. Baker, C.E., in his work ** On the Strength of Beams, Columns, and _ Arches,” pp- 8, 9, 10, goes into this subject, and affirms that the neglect of this force in the beam leads to errors of any amount up to 190 per cent., being little or nothing in iron girders, where the bulk of the metal is collected together in flanges as far as possible from the neutral axis.
 * rganisation, as a force in art, did not, and