It is no secret that the moon has no light of her own, but is, as it were, a mirror, receiving brightness from the influence of the sun.

There will be natural propriety in using an eastern light for bedrooms and libraries, a western light in winter for baths and winter apartments, and a northern light for picture galleries and other places in which a steady light is needed; for that quarter of the sky grows neither light nor dark with the course of the sun, but remains steady and unshifting all day long.

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

Some have held that there are only four winds: Solanus from the east; Auster from the south; Favonius from due west; Septentrio from the north. But more careful investigators tell us that there are eight.

There are many names for winds derived from localities or from the squalls which sweep from rivers or down mountains.

There are also in some places springs which have the peculiarity of giving fine singing voices to the natives, as at Tarsus in Magnesia and in other countries of that kind.

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