The great collecteur d'Asnières, a sectional view of which under the Rue Royale, is shown on page 299, is five mètres, sixty centimètres, in width, and three mètres, forty, in height; the channel for the water in the centre is three mètres, fifty, in width, and one mètre, thirty-five, in depth. On each side is a _banquette_, or sidewalk, ninety centimètres wide. The collecteurs, as well as the smaller sewers of the streets and houses, are constructed of masonry laid in mortar, and they are lined with cement which insures their cleanliness and their sonorousness. The former quality is maintained by an incessant surveillance, an organized force of nine hundred and thirty-one men being constantly employed, and an arrangement of fans or wings, mounted either upon the fronts of the boats or attached to the bottoms of the little trucks which run on rails along the edges of the canal of the larger sewers. These fans descend into the canal and sweep all obstructions before them,--the sand from the street pavements overhead constituting a large portion of this obstructive material. The siphons are cleansed by an ingenious process invented by Belgrand and applied by him to that of the Alma,--a large wooden ball, eighty-five centimètres in diameter, traversing twice a week each of the two conduits, a mètre in diameter. So thorough is this policing of the sewers, that it is recorded that the number of heavy leathern thigh boots furnished the _égoutiers_ is some twelve hundred or two thousand annually, representing a value of nearly a hundred thousand francs. One pair of these boots lasts about six months.