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POPULAR SCIENCE REVIEW. 
one 150 feet square, and the other 150 feet by 86 feet wide. 
All these are 50 feet high, covered with glass, and lighted from 
above. They ai'e the only parts which resemble the Crystal 
Palace. 
One important feature in which the Exhibition of 1862 differs 
from that of 1851 , is the Refreshment-rooms and Arcades. They 
are built of brick, and overlook the whole of the Horticultural 
Gardens. Unlike its predecessor of 1851, where the refresh- 
ments were confined to biscuits, soda-water, and buns, those 
of the present Exhibition will be on a large scale, every descrip- 
tion of refreshment being supplied in spacious dining-rooms 
300 feet long by 75 feet wide; and the arcades on each side will 
be collectively about 1,500 feet in length and 25 feet in width. 
The Annexe or machinery compartment, which extends along 
the west side of the Horticultural Gardens, is composed of four 
spaces, each 1,000 feet long and 50 feet wide, covering- an area 
of 50,000 square feet. The whole of these constructions com- 
prises a “ ridge-and-valley ” roof, composed of a very cheap 
material, and of very simple construction, namely, deal boards, 
nailed together in the form of arches, which spring from vertical 
standards of two 21-inch planks nailed together to a height of 28 
feet. These, again, support the gutter plank, where the feet of 
the rafters terminate, a little below the intrados of the curved 
arch. The roof frames are boards nailed together, and so disposed 
that the weight comes direct on their edges. The lower part of 
the roof is covered with boards and felt, and the upper part is 
glazed with skylights, having bearers for ventilation throughout 
the whole length of the three divisions. 
This department of the Exhibition will be devoted entirely 
to machinery in motion ; and, in order to give every facility to 
exhibitors, a large supply of steam from six 50-horse boilers, 
placed at the north-west corner of the Horticultural Gardens, 
will be conveyed in pipes laid in a tunnel the whole length from 
north to south, at the cost of the Commissioners. Provision is 
also made, by the introduction of large wrought-iron pipes, for 
carrying the exhausted steam clear of the buildings, from 
the numerous engines supplied by the exhibitors ; and these 
again, with the necessary shut-off valves, will constitute the 
motive power to be employed in driving every description 
of machinery submitted for public inspection. In addition to the 
steam required for these purposes, upwards of 2,300 feet of 
2 1 -inch polished shafting will be extended, at a height of 
1 0 feet from the floor, for the accommodation of the exhibitors. 
The shafting will be supported on neat cast-iron columns, 
extending: at convenient distances in lines along- the middle 
of the different divisions, and of suitable lengths calculated 
to meet the requirements of the exhibitors and give motion 
