64

CONSTRUCTION OF THE BUILDING.

The lead Hats.

The externalenclosures'

Fig. 14.

Transept llihs.

diameter, arc fixed small ribs of wood, which being connected with the main andminor ribs by means of sash bars, become available as ridges. The space between

them and the ribs is glazedand finished on the same sys-tem as that adopted in the flatroof of the building, the sashbars being set at an obliqueangle, or “ herring - bone ”fashion, in order to assist theconduction of the water, andprevent its lodging against thelower putty bed of each paneof glass over which it trickles.

Along the summit of thissemi-cylindrical vault runs,from north to south, a narrowlead path, in order to affordaccess to the apex of the roof,and to provide a means of low-ering down workmen to repairany damage that may possiblyhappen to it. As the quantityof water discharged from thisvault must necessarily be con-siderable, it was deemed advi-sable that the 24-feet aisles oneach side of it should be

covered with lead flats, insteadof the ordinary glass roofing.These lead flats presented alsothe further advantage of beingso completely connected, as toform solid abutments, steady-ing the feet of the ribs. Inorder to convey any pressurein the way of thrust, that theribs might exert, to those

Section of Transept Rib, and springing of ditto. points best Capable of TCSlSting

strain, horizontal trusses of wrouglit-iron were constructed beneath the leadflats, consisting of bars capable of being keyed up at any time from the

lead flats, and thus any tendency to movement, on the part of any of the

ribs, would be immediately transferred either to the extreme north and southends, where their feet are securely tied together by the cast-iron girderswhich cross the transept at those points; or to the angles where the transeptintersects the nave, and where the whole force of the vis inertias of the nave roofwould serve as abutment.

The general effect produced by this semi-cylindrical roof covering the largeelms beneath, is shown in Plate I.

The external enclosures or walls, as seen from within, on the two upper

;

Inltm/glia/lc

mmmm.