1843.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



163 



Unfortunately this discrepancy in theory extends itself to data given 

 as the result of practice and actual experiment, and adds infinitely to 

 the difficulty of arriving at anything like a satisfactory result in inqui- 

 ries of this kind. As instances, I may state that Rondelet, a French 

 writer of much celebrity, gives a force of 50001b. on the square inch, 

 to crush a piece of oak, and upwards of 6000 lb. to crush fir ; whereas 

 Mr. George Rennie, in his elaborate and detailed experiments, found 

 English oak to crush with 38G01b. to the inch, and fir with 1028. The 

 result of all experiments on wood, however, go to prove that the re- 

 sistance increases in a much higher ratio than the mere area of the 

 material. 



Mr. Rennie found Portland stone to crush with 12841b. to the 

 square inch. Messrs. Bramah, in their experiments in 1837, found 

 10201b. crush it; whilst a central stone shaft at Anjou Cathedral, 

 which is considered a remarkable specimen of lightness, bears only 

 5001b. to the square inch, though calculated by Mr. Gauthy to be 

 equal to the resistance of 3-170 lb. to the inch. 



It is probable that few experiments were made actually on the 

 same data, the stones are not of equal quality, the wood unequally 

 seasoned ; and when we remember that oak timber loses 30 per cent 

 of its weight in seasoning, these differences are to some extent ex- 

 plained. 



Believing that one sound practical opinion would avail more in 

 this case than any theory, I have sought the opinion of those mem- 

 bers of our profession, and of those of the engineers, in whose 

 judgment on such points I have the greatest confidence, and they have 

 without one exception confirmed my belief, that if the outward thrust 

 of the roof is removed, these ties may be taken away. I had the 

 benefit of the opinion of Captain Dennison, (Government Engineer at 

 Woolwich,) who examined the whole building with me most carefully, 

 and who fully concurs in this view of the question. We tested the 

 upright lines of all the outer buttresses, and we found that with very 

 little variation, they had all gone outwards, from the perpendicular, 

 between 34 and 4 in. to the springing line, even those immediately 

 adjoining the staircase and cloister walls, where naturally the abut- 

 ment is greatest ; proving, as we think, that this must have been the 

 effect of one uniform thrust, when the centres were first struck, and 

 the whole groin took its bearing. We found the iron bars slack, 

 hardly any of them being strongly in tension. 



The centre pillar has gone over towards the east considerably, to 

 the north-east 3| in., to the east 4| in., and to the south-east 3| in., an 

 injury we believed to have been much more caused by the irregular 

 thrust of the heavy roof than by any action of a groin, which from its 

 abutments having all equally decayed, must have been nearly " in 

 equilibrio." The stone ribs show hardly any trace of the necessary 

 contraction and exi>ansU>f which must have taken place when this 

 pillar went over ; and the chalk groin shows no settlement that gives 

 cause for alarm. Having then satisfied myself as far as possible of 

 the practicability of removing these iron ties, we propose to shove up 

 the centre column, these timbers having been brought to their bearing 

 (the weight they have to carry being 115 tons). I propose to take 

 down the present central shaft, with its eight surrounding ones, to 

 plumb a perpendicular line from the centre of the octagonal stone 

 above the capital, and from this centre to carry up, on the old foun- 

 dation, the central pillar, making good, with Purbeck marble, such 

 ones as may be found to have perished. This foundation is com- 

 posed of concrete of the best description, and evidently laid before 

 its reputed father, Sir R. Smirke, could have introduced it into this 

 country. This effected, and the groin left to its proper bearing, (the 

 iron ties still being untouched,) I propose to take off the present heavy 

 roof, and in its place to substitute, as I strongly hope, the high 

 pitched one, the feet of the principal rafters being laid into cast 

 iron shoes, held together, or rather in their places by eight wrought 

 iron tension rods, ]i in. diameter, having an eye at the end nearest 

 the centre, into which the suspension rod (thickened at its lower end 

 to 3 in. diameter) would fall, and hold up the tension rods. This 

 roof, if adopted, would render unnecessary the piece of timber now 

 resting on the centre column. The sprandrils of the groin I propose 

 to fill to the height shown by the red tint. That this was the original 

 form of roof, I believe there can be little doubt, a view in which I 

 have been confirmed by Mr. Pugin, who has carefully studied this Ca- 

 thedral, and who speaks most confidently to the point; to suppose it 

 otherwise, would be to imagine that in this building they had thrown 

 overboard the vertical spirit of the Cathedral roof, and of all roofs of 

 that size of which we have any trace. Having satisfied myself that 

 the further perpendicular weight which would by this means be 

 thrown on the buttresses, in addition to that of the groin, could have 

 no crushing effect, the weight each buttress would have to carry 

 being 62 tons, which distributed over the area of each, gives a weight 

 of 594 lb. to the square inch ; whilst the capabilities of Chillmarke 



stone (taken at four-fifths the lowest given for Portland) would re- 

 quire 823 lb. to the inch to crush it. The centre shaft bears 10001b. 

 to the squ are inch. Rondelet says " there can be no danger in making 

 stone bear one-third the weight which would crush it;" it is therefore 

 fair to suppose there can be none in giving it one-fourteenth; and in 

 this calculation 1 have made no allowance for the increased tenacity 

 afforded by an increase of superficies. This risk being avoided, the 

 additional resistance thus afforded to the thrust of the groin by the 

 weight above, would be considerable. Of the value of this heavy 

 superstructure, Sir Christopher Wren was fully aware. In his report 

 on Salisbury Cathedral, he says, " As for the vaults of the ailes, they 

 are indeed supported on the outside by the buttresses, but inwardly 

 they have no other stay but the pillars themselves, which as they are 

 usually proportioned, if they stood alone without the weight above, 

 could not resist the spreading of the ailes one minute." 



Should, however, the Chapter (whose consent to any plan must be 

 obtained) object to the high form of roof, and require the new one to 

 retain the pitch of the present one, and not to rise above the parapet, 

 their decision must be final, and in that case I should propose to adopt 

 this roof, which though simple enough in its construction, has at least 

 this advantage over its predecessor, that it causes no outward thrust. 



In either case lead would form the covering. The roof being made 

 perfect, and all defects in the external masonry having been made 

 good, I propose gradually to loosen the nuts which are now attached 

 to the iron ties, watching most carefully if any fresh thrust follows. 

 Those bars I propose to re-introduce above the groin and immedi- 

 ately under the roof. They would form a perfect tie at this level, and 

 if unluckily any accident or failing shall take place in the cast-iron 

 shoes or tension rods of the roof truss, these bars would then come 

 into play, and would prevent the effect of any lateral thrust. The 

 internal stone work we hope gradually to restore. The stone seat 

 and step running round the Chapter House will be taken up, cleaned 

 and re-laid, making good with new stone. Under this seat, it is pro- 

 posed to form a Hue in brickwork, into which would be introduced 

 from a stove, to be built under the stairs, a current of warm air, 

 having vents through, and stone ornaments on each face of the oc- 

 tagon, thus keeping the building free from the damp which now 

 disfigures it. 



It is proposed to relay the whole floor (containing 236 yards) with 

 encaustic tile paving, of similar design and colour to those now ex- 

 isting ; and instead of their being laid on the earth as at present, 

 which has tended to make the floor damp and irregular, I propose to 

 have a thin bed of concrete made with water lime formed over the 

 whole surface not occupied by the foundations. 



The plastering to the soffit of the groin, which now exists, is in a 

 defective state, cracked and discoloured. It will be repaired and re- 

 coloured ; and as the chalk groin is of rude and irregular surface, it 

 perhaps will be desirable to reline it as it now exists, restoring the 

 present coloured ornaments which now diverge from the bosses. 



I have now only to allude to the windows. It is years since the 

 last window of stained glass existed in the Chapter House. It was 

 then taken down and used iu the restoration of some of the Cathedral 

 windows. If there ever existed a building in which colour was an es- 

 sential ingredient, it is this ; and I have every confidence that if the 

 restoration, to which I have already alluded, can be satisfactorily car- 

 ried out, that it will not be a very distant period before these windows 

 will be filled with glass, whose colours shall be not less rich and 

 harmonious than those which originally decorated this interesting 

 building. 



Iron Snips.—" The Iron Queen."— We find that iron, as a material for ship- 

 building, is fast gaining ground. For steamers, iron has been a favourite 

 for some time past; ami there is not now one wooden steamer building at 

 this pint, while we observe there are two iron ones, of the first class, nearly 

 completed, and, we understand, contracts are made for the building ol three 

 more. We are also now satisfied, that the only objection to sailing vessels ot 

 iron, namely, the getting foul during a foreiyn voyage^ :s ijumpK lely 

 removed.. This is prov 



;giste 



is proved by the result of two voyages ot the Iron <Jn;-:i. 

 This barque, 350 tons register, left the river Tyne in February 1842, with U 1 

 tons of coals for Havana ; from thence she went to Mobile for a cargo ol 



.otton for this port. She has now completed another voyage, from this port 

 to Galveston, in Texas, carrying 300 tons of salt out, and a full cargo ol 

 cotton home. She has been in the Graving dock, where she was Visited by 

 many persons, and she is found not to have strained a single rivet, although 

 she struck heavily on Galveston Oar. There is no appearance ol corrosion, 

 the red lead being fresli on the plates; and neither shells, barnac.es. nor any 

 foulness, was on her bottom. This desirable result is caused by the simple 

 application of a compound of tallow, bright yarni !i. arseni . an I brim itoi e, 

 which effectually destroys marine, vegetable, and animal substani ' 



Iron Queen was built by Messrs. John Vernon and Co.. of Aberdeen, and h 

 proved very creditable to their skill as builders. The surveyors lor Lloyd's 

 here are so h ell satisfied that there is no corrosion that they have classed her 

 A. 1. — Liverpt ol i 



22 



