The main effluent-drain has a cross-section for the whole length of the filter of 4.73 square feet, or 1/17000 of the area of the filter; and even at the low rate of filtration proposed, the velocity in the drain will reach 0.97 foot. The drain has brick sides, 1.80 feet high, covered with granite slabs. The lateral drains are all of brick with numerous large openings for admission of water. They are not ventilated, and I am unable to learn that any bad results follow this omission. The filling of the filters consists of 2 feet of gravel, the top being of course finer than the bottom layers, above which are 40 inches of sand, which are to be reduced to 24 inches by scraping before being refilled. The water over the sand, when the latter is of full depth, is 43 inches deep, and will be increased to 59 inches with the minimum sand-thickness. The apparatus for regulating the rate of filtration was described page 52. The cost of the entire plant, including 34 acres effective filter-surface, 40 acres of sedimentation-basins, over 2 miles of 8-1/2-foot conduit, pumping-machinery, sand-washing apparatus, laboratory, etc., was about 9,500,000 marks, or $2,280,000. This all reckoned on the effective filter area is $67,000 per acre, or $3.80 per head for a population of 600,000. The death-rate since the introduction of filtered water has been lower than ever before in the history of the city, but as it is thought that other conditions may help to this result, no conclusions are as yet drawn. DEATHS IN HAMBURG FROM ALL CAUSES, AND FROM TYPHOID FEVER, BEFORE AND AFTER THE INTRODUCTION OF FILTERS.