One more process made the sash-bars complete for fixing--this was the drilling a hole at each end to nail them down on the gutter and ridge; and this was also done by machinery, to insure all the holes being drilled at the same angle. On one side of a horizontal bench were placed a set of four-inch driving pulleys (_a a_), with as many horizontal drills projecting towards the other side of the bench; a wooden traversing-plate (_c_) opposite each drill, and working towards it, received one end of the sash-bar, while the other rested in an inclined position against a wooden rail (_b_) placed longitudinally above the pulleys, having as many sinkings thereon as there were drills. The traversing-plate being then pushed forward, the sash-bar was perforated by the drill; the plate was then drawn back, and the same operation repeated with the other end of the bar, which left it ready for fixing. The action of the traversing-plate (_c_) is shown more distinctly in the second engraving.[7] One out of every nine of the sash-bars of the roof is stronger than the rest, to serve for fixing the ridge previous to glazing. These extra-strong bars are two inches wide and one inch and a half deep, and were formed by the same machinery already described, by an adjustment of the different cutters and saws. [Illustration: PORTION OF SASH-BAR DRILLING-MACHINE.] The Ridges. The total length of these required was about sixteen miles. They are cut out of timber three inches square, in section, and are of the form shown in the diagram, with a groove on each side to receive the glass. This was also done by machinery which, with about five-horse power, turned out one hundred lengths of twenty-four feet in a day of ten hours, allowing the time for the necessary stoppages. After they had been delivered at the building, these ridge-pieces were cut to the exact lengths by means of the same apparatus used for the solid gutters which has already been described. At each end of the ridge-piece two holes were also drilled to receive dowells to connect it with the adjoining length. By no other than mechanical means could the immense number of holes thus drilled have been placed so exactly that those in the opposite ends of any two ridge-pieces should correspond precisely. [Illustration: SECTION OF RIDGE AND ORDINARY SASH-BAR.] The different essential component parts of the roof having thus been described, we propose to take the different members of the construction in succession downwards. The Glass.