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first consider the flow of water through porous rocks: Darcy’s law (see Chap-
man, 1981, pp. 49-72, for a fuller account).
Henry Darcy (1856; his name is so spelled) experimented with sand filters
in the context of public water supply to the town of Dijon in France. Using
apparatus shown diagrammatically in Fig. 8-8, he found that the volumetric
rate of discharge was proportional to the difference of levels in the mano-
meters and inversely proportional to the length of the sand filter (Fig. 8-9).
The equation he deduced is, in the notation of this book:
q = &/A = KAh/l (8.6)