4 CANNING COLLEGE, LUCKNOW.
arch with elliptical ribs, has been made elliptical throughout, the span of plain portion being 45 feet and of ribs 43} feet; these latter are dis- posed in pairs immediately over Corinthian pilasters. The east end of roof which is elliptical in plan is domed to meet the straight portion. The whole of the arching springs at a height of 312 feet above floor level, and has a versine of 15 feet. The thickness of plain portions of roof is 14) inches at crown, increased to 224 inches at haunches; where the ribs occur these dimensions are increased by 9 inches.
The arch was built on a Hindustani centre supported by pillars of brick- in-mud placed about 8 feet apart, the exterior of centre was worked rough- ly to shape and finished with lime mortar, the true shape being obtained by use of templets made for the purpose; the arch was built in lengths of 15 feet, so that each joint comes between a pair of ribs. The whole roof was built and keyed in 15 days, being completed on the 23rd June 1878; there was some little delay in getting the backing up to the required height, and the centering was not wholly struck until the 1st August. Levels taken at 10 feet intervals along the top of arch just after keying up and after centres were wholly struck, showed the maximum settlement to be G•1 foot and minimum 0.05 foot, the mean being 16-inch. In the straight portion of the roof the thrust is taken by 4" x 4" x Ş" L-irons placed 6 feet above springing and connected by tie-rods 14-inch diameter placed 75 feet apart. The spandrels are filled with concrete as for foundations, and a 3 inch layer of terrace is given over the whole.
The floors throughout the building are of Mirzapore stone slabs 2' X 2' x 2" set in 2 inches of lime mortar over brick rubbish carefully rammed.
The central rectangular and corner turrets have Mirzapore stone pil- lars and lintels, the arches between the pillars are cut in 4-inch stones which are let 2 inches into both pillars and lintels; the joints are set in fine lime mortar, and the lintel stones are held firmly together by iron cramps run in with sulphur; the pillar bases and caps are secured by vertical iron dowels also run in with sulphur. The roofs and work above lintels is entirely of 1st class brickwork, in rectangular turret the roof is a semi-circular arch 14 inches thick, and the corner turrets are domed thrust bands of 4" x " iron being built in at a height of 2 feet above springing ; round these corner turrets there are projecting balconies
supported on stone brackets 2 inches thick, these brackets project 4 feet
4
