CONSTRUCTION OF NEW READING-ROOM, &C. 



9 



be seen; still it was a beginning, and laid the foundation. 

 Within three years the vast structure has been completed, 

 at the cost of 150,000/., or about that sum when all con- 

 tingent expenses are accounted for. 



Construction of New Reading-Eoom and Libraries. 

 **The Reading-room is circular. The entire building does 

 not occupy the whole quadrangle, there being a clear interval 

 of from 27 to 30 feet all round, to give light and air to the 

 surrounding buildings, and as a guard against possible de- 

 struction by fire from the outer parts of the Museum. The 

 dome of this Reading-room is 140 feet in diameter, its 

 height being 106 feet. In this dimension of diameter it is 

 only inferior to the Pantheon of Rome by 2 feet ; St. Peter's 

 I being only 139; Sta. Maria in Florence, 139; the tomb of 

 ; Mahomet, Bejapore, 135; St. Paul's, 112; St. Sophia, Con- 

 stantinople, 107, and the Church at Darmstadt, 105. The 

 new Reading-room contains 1,250,000 cubic feet of space; its 

 'suburbs,' or surrounding libraries, 750,000. The building 

 is constructed principally of iron, with brick arches between 

 the main ribs, supported by 20 iron piers, having a sectional 

 area of 10 superficial feet to each, including the brick casiug, 

 or 200 feet in all. This saving of space by the use of iron 

 is remarkable, the piers of support on which our dome rests 

 only thus occupying 200 feet, whereas the piers of the 

 Pantheon of Rome fill 7477 feet of area, and those of the 

 tomb of Mahomet 5593. Upwards of 2000 tons of iron have 

 been employed in the construction. The weight of the 

 materials used in the dome is about 4200 tons — viz. up- 

 wards of 200 tons on each pier. The first standard was only 

 fixed in January, 1855. The framework and scafi'olding 

 upon which the dome rested were removed on the 2nd of the 

 following June. No subsidence or 'set' of material was ob- 

 servable on the wedges being removed. The entire dome 

 was roofed in and copper covering laid in September, 1855. 

 The roof is formed into two sepai-ate spherical and con- 

 centric air chambers, extending over the whole surface; one 



