Wind is a floating wave of air, whose undulation continually varies.

Bricks should be made in Spring or Autumn so that they may dry uniformly.

Bricks will be most serviceable if made two years before using; for they cannot dry thoroughly in less time. When fresh undried bricks are used in a wall, the stucco covering stiffens and hardens into a permanent mass, but the bricks settle and the motion caused by their shrinking prevents them from adhering to it, and they are separated from their union with it. At Utica in constructing walls they use brick only if it is dry and made five years previously, and approved as such by the authority of a magistrate.

I am moreover inclined to be concise when I reflect on the constant occupation of the citizens in public and private affairs, so that in their few leisure moments they may read and understand as much as possible.

Next I must tell about the machine of Ctesibius, which raises water to a height.

Our ancestors, when about to build a town or an army post, sacrificed some of the cattle that were wont to feed on the site proposed and examined their livers. If the livers of the first victims were dark-coloured or abnormal, they sacrificed others, to see whether the fault was due to disease or their food. They never began to build defensive works in a place until after they had made many such trials and satisfied themselves that good water and food had made the liver sound and firm, healthfulness being their chief object.

The design of a temple depends on symmetry, the principles of which must be most carefully observed by the architect.