Having thus given a general sketch of the arrangement and appearance of the building, we shall proceed to describe somewhat more minutely the various details of the construction, of which the essential parts are few in number compared with the great repetition of each individually. To assist in this multiplied reproduction of the same form, some exceedingly ingenious machinery has been employed, which will therefore be described in connexion with the parts it has been used to form; and thus these will be traced through their various stages, from the raw material to their finished state as portions of the building. The greater part of this machinery has been used in shaping out those parts which are of wood, and particularly the different portions of the roof, with which we will therefore commence. The Paxton's Gutters. It has been mentioned that the rafters which span the space between the roof-girders serve, at the same time, as gutters, for which purpose they are hollowed out on the upper face, besides having smaller grooves at the sides to take the condensation-water. The bottom of the gutter is of a circular form, which is universally considered the best for conveying liquids with the least amount of friction, and therefore the least liable to obstruction from an accumulation of dirt. [Illustration: SECTION OF THE PAXTON'S GUTTER, WITH THE STRONG SASH-BAR.] [Illustration: THE CIRCULAR PLANING-MACHINE.] [Illustration: PORTION OF PLANING-MACHINE, WITH THE REVOLVING ARM AND CUTTERS.]