MECHANICS AND USEFUL ARTS. 7 



consists of a main avenue, 408 feet long by 72 feet wide, and two 

 aisles, each 408 feet long by 24 feet wide. The larger of these areas 

 is spanned by the semi-cylindrical roof, formed of semi-circular ribs, 

 the ends of which are inserted in the hollow columns ; these ribs are 

 strengthened by stout timbers, placed between the ribs, and at right 

 angles to them, and which act as purlins, and great intermediate sash- 

 bars. " Upon this simple and effective system," observes Mr. Saunders, 

 " sixteen light and strong ribs have been made to span a width greater 

 by one foot than the nave of Westminster Abbey, including its side aisles, 

 and that at an elevation greater by six feet." 



In order to provide for a ventilation of the building, the whole of the 

 basement part, to the height of four feet, was made of louvre boarding; 

 and at the top of each tier of galleries a similar provision of three feet 

 was provided. By a simple arrangement of machinery, the whole of this 

 louvre boarding can be opened and closed instantaneously, with the 

 greatest facility. To modify the intensity of the light, and at the same 

 time to aid in keeping the building cool, the inner side of the roof was 

 painted sky-blue, and the outer covered with canvas attached to the 

 ridges throughout the flat roof. This latter arrangement also dimin- 

 ishes the chances of leakage from imperfect jointing or broken glass. 

 The method of flooring to the building was after a plan adopted by Mr. 

 Paxton in the construction of horticultural edifices, viz., trellised wooden 

 boarding, with spaces between each board, through which all dust, on 

 sweeping, falls into the vacuity below. 



The arrangement of galleries, which form an essential part of the 

 building, is as follows : There are four main galleries running the whole 

 length of the building two on the north and two on the south side of 

 the great central aisle, the whole being connected by two cross galleries, 

 one at either end of the building ; besides twenty intermediate trans- 

 verse gangways, or crossings. The collective length of the galleries, 

 restricted to the second tier, is 9456 feet, or more than one mile and 

 three quarters, and the width 24 feet ; so that the whole area, or surface 

 of gallery-flooring, is equal to 210,240 superficial feet, or nearly five acres. 

 The exposed sides of the galleries are protected by an ornamental iron 

 railing. 



Decorations of the Building. The decorations of the building were 

 carried out under the direction of Mr. Owen Jones, on a somewhat 

 novel and ingenious plan. By the system of coloring adopted, every 

 line in the building was marked distinctly, thus tending to increase the 

 appearance of its height, its length, and its bulk. Externally the main 

 lines are a delicate blue upon a white and stone-colored ground. In 

 the interior, the principal portions of the roof, of a delicate blue tint, 

 harmonize most brilliantly with the light of the sky, beaming through 

 the crystal roof. The transept is artistically splendid ; the under side 

 of each of the twenty-four ribs corresponds in color with that decorating 

 the square fillets of the columns supporting the ribs, viz., light blue ; 

 the part of the under side corresponding to the circular surface of the 

 column is in deep chrome yellow ; upon each side of this color is a 

 stripe of white, dividing it from the blue; upon the smaller ribs, the 

 " returns " are colored red, the edges chrome, and the sides blue ; the 



