The Poiseuille type of equation for capillaries of any shape takes the form, for capillaries of any cross-section, where k0 = 2 and m = r/2 for a circular capillary of radius r, and k0 has generally values between 2 and 3 for other shapes1. Application of this to granular beds follows by putting u = ue. ɛ. L/Le, m = ɛ/Sσ(1 — ɛ), k = k0. (Le/L)2, whence k is known as Kozeny's constant, and is approximately equal to 5 1,2, δp is pressure drop in dynes/cm.2, and other symbols are as in the paper of Lea and Nurse2.