§ 1. In § 3 of Chap. III., it was stated that when a wall had to sustain an addition of vertical pressure, it was first fitted to sustain it by some addition to its own thickness; but if the pressure became very great, by being gathered up into Piers.

I must first make the reader understand what I mean by a wall's being gathered up. Take a piece of tolerably thick drawing-paper, or thin Bristol board, five or six inches square. Set it on its edge on the table, and put a small octavo book on the edge or top of it, and it will bend instantly. Tear it into four strips all across, and roll up each strip tightly. Set these rolls on end on the table, and they will carry the small octavo perfectly well. Now the thickness or substance of the paper employed to carry the weight is exactly the same as it was before, only it is differently arranged, that is to say, “gathered up.” If, therefore, a wall be gathered up like the Bristol board, it will bear greater weight than it would if it remained a wall veil. The sticks into which you gather it are called Piers. A pier is a coagulated wall.