524 



CARPENTRY. 



Construe- ever grandeur or decoration was required, they were 

 tive never omitted. They became the most principal or- 

 Carpentry. nament o f t h e times, and formed the most conspicuous 

 features in the edifices in which they were employed. 

 At first they were used in the same manner as by the 

 Romans. 



In after times the groins were supported upon ribs 

 which sprung from cylindrical or polygonal pillars, 

 with capitals of the same form. This produced a ne- 

 cessary change in the figure of the vaulting, as the 

 bottom of the ribs rise from the circumference of a 

 circle, instead of the angles of a square, with its sides 

 parallel to the walls; and as the spaces between and 

 over the ribs were vaulted in a twisted or winding 

 surface, so as to coincide in every part with a straight 

 line, level between the ribs ; the angles of the groined 

 surface were thus very obtuse at the bottom, but di- 

 minished continually upwards, and ended in a right 

 angle, at the summit of the ceiling. Afterwards, 

 when the pillars were formed upon a square plan, 

 diagonally placed with regard to the sides of the 

 building, and decorated with vertical mouldings, or 

 small attached columns, and the number of ribs in- 

 creased, the first idea of fan work would be presented 

 at the springing of the ribs. But in this the archi- 

 tects would soon perceive an incongruity of form in 

 the surface : as it approached the summit of the 

 vaulting, the ribs would be formed all of equal radii, 

 and disposed around to support a concavity which 

 might be generated by revolving a curve round an 

 axis which was in the centre of the pillars ; and being 

 accustomed to groins meeting in lines crossing each 

 other, it was natural to suppose they would at first 

 permit the ribs to run out and meet each other, which 

 would then be of unequal lengths. If the difference 

 between the openings was not very great, the lines 

 thus formed, by the meeting of the opposite sides of 

 the vaulting, would not differ materially from straight 

 lines, but would not be parallel to the horizon, as 

 they would run upwards towards the centre of the 

 groin ; but this would depend on the angle formed 

 by two opposite ribs in the same plane. Thus if the 

 tangents. formed at the vertex of the opposite curves 

 contained an angle of 120 degrees, the apex line on 

 the ceiling would form a curve, in receding from the 

 vertical angles of the said ribs, of a very decided con- 

 vexity ; but in going progressively forward, the cur- 

 vature would change into a concavity, and then 

 would begin again to descend. The idea of intersect- 

 ing the ribs thus disposed in vertical planes around a 

 common axis, by circular horizontal ribs, was natural; 

 and this again would generate another idea of sup- 

 porting the upper ends of the ribs by a circular ring, 

 concentric with the axis of a pillar ; and thus being 

 done from four pillars, would leave a space inclosed 

 by four convex arcs of circles. Nothing farther was 

 required to complete this system of vaulting than to 

 fill up the space, and the whole would be keyed to- 

 gether. In this manner, by slow and imperceptible 

 changes, a species of vaulting was invented very dif- 

 ferent from that of the Greeks and Romans. In- 

 *tead-of closing the space, if we suppose another ring 

 forming a complete circumference to be built interi- 

 qrly to touch the former arcs, and the four triangu- 

 fyr curved spaces closed and wedged together with 



masonry, the whole will stand equally firm as if the Construc- 

 midille had been solid ; and thus an aperture for light fl ' ve 

 Will be formed the same as in dome vaulting. Carpentry. 



The only improvement made by the moderns in > ~*^^** / 

 vaulting, is the cylindro-cylindric arche-, which are 

 made in opposite sides of a vault, and when regular- 

 ly repeated, have a very beautiful effect. 



In warehouses, which are loaded with the greatest 

 weights, and where the walls are placed at a remote 

 distance, it becomes necessary to introduce many sup- 

 ports to the floors, which if constructed of timber 

 are liable to both fire and rot, and thereby exposed 

 to sudden danger; every precaution should there- 

 fore be taken to prevent the risk to which they are 

 thus exposed ; at least as far as may appear eligible 

 in the profits arising from the articles to be deposit- 

 ed making a full compensation for the additional ex- 

 pence. The end will be fully answered by the intro- 

 duction of groins, which not only answer the same- 

 purpose as the flooring of timber work and the 

 wooden posts which support it, but are more dur- 

 able, and a certain proof against both fire and rot. 

 Though groins are only employed in the lower sto- 

 ries or buildings, owing to the great expence which 

 would be incurred by the great thickness of walling 

 and the diminution of space which would be occa- 

 sioned thereby, they may at all times be used in cel- 

 lars and ground stories, without much additional la- 

 bour or expenditure of materials. 



It has been found that brick groins, rising from 

 rectangular piers, are inadequate to the weight they 

 have to support, and incommodious to the turning 

 of goods round the corners of the piers. An improve- 

 ment has been suggested by Mr George Tapen, ar- 

 chitect, in a small pamphlet lately published, where 

 he judiciously recommends the piers to be construct- 

 ed octagonally, and the square angles of the groin 

 to be cut off equal to the breadth of the side of the 

 octagonal piers. He gives a very satisfactory reasoi* 

 to this purpose, that the angles of groins built in 

 the common way, forming a right angle, are hardly 

 capable of sustaining themselves, and much less the 

 load which is required to be supported, owing to the 

 bricks being so much cut away at the angles in order 

 to fit them thereto, that they have little or no lap 

 upon each other. This scheme should certainly be 

 carried into practice wherever groins are applied to 

 such uses. 



In the construction of edifices for dwelling, they 

 ought always to be employed in cellars and other 

 damp situations, and particularly in cellars which 

 have paved apartments above. 



Groins for use only, may either be constructed of 

 brick or stone as the material of the one or the other 

 may be more easily procured. If they are only to be 

 employed by way of proportion or decoration, their 

 beauty depends on the generating figure of the sides, 

 the regularity of the surface, and the acuteness or 

 sharpness of the angles, which ought therefore to be 

 rendered obtuse. In the best buildings, where du- 

 rability and elegance are required at the same time, 

 they may be constructed of wrought stone ; and where 

 elegance is wanted at a small expence, of plaster, 

 supported by timber-work. 



Groinvare constructed upon two different ways, 



