various points there are galleries and staircases, to descend to the subterranean aqueduct. I descended to examine the work with M. Girard, the engineer, by a flight of steps from the cellar of a house where one of the guardians resided. " Convenient arched passages are constructed under three principal streets, where one may walk, and where are laid the different mains taking water from the aqueduct, to conduct it to the various fountains and other points for distribution. They are laid upon stone blocks or cast iron frames, so that they may be easily examined all round, from one end to the other. The beautiful fountain in the Garden of the Palais Royal, that in the Boulevard of Bondy, &c. are supplied from this water. " The canal is estimated by Mr. P. S. Girard the engineer who constructed it, and had the whole superintendence of distributing the water in Paris, at 4000 inches of water, (polices tfeau de fontainier.) An inch of water is so much as will flow through a hole one inch diameter, French measure, in a minute, under a head of 7-12 of an inch above the centre of the aperture, and is equal to 813 1-2 cubic inches in a minute, or 678 cubic feet in 24 hours, amounting to 2,711,680 feet for the 4000 inches daily, or over 20 million gallons. " The quantity of water necessary for a given number of inhabitants has not been accurately fixed. In France it has been generally estimated at 19,195 litres (one inch) for 1,000 inhabitants. The Scotch engineers do not consider the supply complete at less lhan nine gallons a day for each individual in a city. If we compare the distribution of water in London with the population, the supply is at the jate of 20 gallons for each person. But there are no public fountains in that city, and the people receive no water but what is furnished by independent companies. At Paris, 4000 inches of water of Ourcq are appropriated for fountains and for cleaning streets, so that water is raised from the Seine for domestic use. The actual quantity thus used does not exceed 200 inches, (equal 135,584 cubic feet daily,) and it costs, from an accurate and detailed estimate, the enormous sum of 4,265,756 francs, equal to $767,836. To supply the want of Seine water, on account of its cost, pumps are employed in nearly all private houses, and spring and well water is used, although it does not possess the qualities suitable for mechanical industry. 17 66 PRELIMINARY ESSAY. " Great inconvenience arises among engineers and hydraulicians, from the want of a standard unit, to denote the quantity of water flowing in a given time. The foun- taineer's inch (pouce d> eau de fontainier) is used by all French writers upon the subject, though admitted by most of them to be very indefinite. It is perhaps sufficiently correct for practical purposes, but not adopted in philosophical investigation. Genieys says, it is ( equal to the quantity of water a pipe an inch in diameter would furnish in a minute, so placed that the centre of orifice should be seven lines below the surface of the reservoir to which it is adapted. To estimate the quantity it is still necessary to determine the length of the pipe or thickness of the side of the vessel in which the aperture is made, through which the water is discharged. Now this has never been done in such a way as that all agree upon the exact amount ; but it is generally admitted to be equal to 15 pints, or 13.33 litres a minute, or 19,195 litres in 24 hours.' " The above are French measures. The litre is equivalent to 61,028 cubic inches ; hence the fountaineer's inch is 813 1-2 cubic inches a minute, or 678 cubic feet a day. Gallon, as used by English writers, is also a very ambiguous term, when applied to hydraulic discharges. The gallon which I employ in this report,= 231 cubic inches ; the beer gallon,= 282 ; and the imperial gallon,= 277,274 cubic inches. " Mr. Geniey's statement is that 19,195 litres (one inch) is generally estimated in France, as a supply for 1000 inhabitants ; which gives 0.6779 cubic feet, or a little over 5 gallons to each daily. Seine water is distributed by carriers in hogsheads or carts, for which they pay at the pumps or filters 6305 francs the inch, and retail again to the inhabi tants for 30,462 francs. The amount thus paid by the Parisians is annually 2,864,504 francs. Another class of water-carriers are those who carry it in buckets, (Porteurs d1 eau a bretelles), hung to straps connected with a kind of yoke over the shoulders. These