Note 105 — Chapter IV · PART I. THE AQUEDUCTS. (continued 2)

The draining of the lakes in the hills round Rome is a great mistake, and very injurious to the health of the city. Such lakes are a wise provision of nature for collecting some of the surplus water in the rainy season, and preserving it for use in the hot and dry season, when the evaporation from the lakes helps to cool the air. The water also drawn from these lakes was most useful for the irrigation of the country round Rome, and watering the gardens in Rome itself, thereby promoting vegetation, which is essential for health in a hot and dry climate. It is well known that the leaves of plants and trees (more especially of deciduous trees) absorb nitrogen, which is the part injurious to human life, and give out oxygen, that portion which is beneficial to, and necessary for, human life. Where there is no vegetation, therefore, the climate cannot be healthy, and without water there can be no vegetation; for water is the necessary food of plants.