Note 4 — Chapter V · Different Types of Earth Dams.
Reading edition
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.