Sands and gravels, flow of water through, 52 (Also see percolation.) Slips and drainage of earthwork, 45 Soil analyses, Tabeaud Dam, 25 analysis, 14 Soils, experiments on filtration through at Wachusett Reservoir, 50 outline study of, 12 permanence of, 51 selection of, for dams, 64 studies, Wachusett Reservoir, 50 Spillway or wasteway, 8 Tabeaud Dam, 31 Subsidences, earthwork, 45 Test pits, 5, 8, 9 Tunnel, outlet, Tabeaud Dam, 30 Tunnels as outlets to reservoirs, 6 Wasteway or spillway, 8, 66 Tabeaud Dam, 31 FOOTNOTES: [1] The writer had intended to present a table of physical properties of different materials, giving their specific gravity, weight, coefficient of friction, angle of repose, percentage of imbibition, percentage of voids, etc., but found it impossible to harmonize the various classifications of materials given by different authorities. [2] The effective head at any point of an earth dam has been defined as the difference in the elevation of the high-water surface in the reservoir and that of the intersection of the down-stream slope with the natural or restored surface of the ground below the dam. [3] This work is very fully described in the Annual Reports of the Metropolitan Water Board of Boston; and by Mr. F. P. Stearns, Chief Engineer of the Metropolitan Water and Sewerage Board, in the Proceedings of the American Society of Civil Engineers for April, 1902. The latter description was reprinted, with the omission of some of the illustrations, in Engineering News for May 8, 1902. [4] By effective size of sand grains is meant such size of grain that 10% by weight of the particles are smaller, and 90% larger than itself; or, to express it a little differently, the effective size is equal to a sphere the volume of which is greater than ¹/₁₀ that forming the weight and is less than ⁹/₁₀ that forming the weight. [5] The term “uniformity coefficient” is used to designate the ratio of the size of the grain which has 60% of the sample finer than itself to the size which has 10% finer than itself. The method of determining the size of sand grains and their uniformity coefficients, is fully explained in Appendix 3 of Mr. Hazen’s book on “The Filtration of Public Water Supplies.”