first, for greater strength; second, to arch between with brick, thus:
Windows opening so that they admit air and not rain. The upper sash opens on a horizontal axis, or pins in the centre of the sides, the lower sash slides up.
Manner of fixing a flag staff on the mast of a vessel: a is the bolt on which it turns; b a bolt which is taken in and out to fasten it or to let it down. When taken out, the lower end of the staff is shoved out of its case, and the upper end being heaviest brings itself down: a rope must have been previously fastened to the butt end, to pull it down again when you want to raise the flag end. Dining tables letting down with single or double leaves, so as to take the room of their thickness only with a single leaf when open, thus:
or thus:
double-leaves open:
