In addition to the economic progress which we have indicated at the beginning, grave problems of public hygiene are connected with that immense question: the sewers of Paris.
Paris is the centre of two sheets, a sheet of water and a sheet of air. The sheet of water, lying at a tolerably great depth underground, but already sounded by two bores, is furnished by the layer of green clay situated between the chalk and the Jurassic limestone; this layer may be represented by a disk five and twenty leagues in circumference; a multitude of rivers and brooks ooze there; one drinks the Seine, the Marne, the Yonne, the Oise, the Aisne, the Cher, the Vienne and the Loire in a glass of water from the well of Grenelle. The sheet of water is healthy, it comes from heaven in the first place and next from the earth; the sheet of air is unhealthy, it comes from the sewer. All the miasms of the cesspool are mingled with the breath of the city; hence this bad breath. The air taken from above a dung-heap, as has been scientifically proved, is purer than the air taken from above Paris. In a given time, with the aid of progress, mechanisms become perfected, and as light increases, the sheet of water will be employed to purify the sheet of air; that is to say, to wash the sewer. The reader knows, that