Forbes was also one of the earliest systematic biogeographers, recognizing a series of provinces in the European (i.e. Arctic, Boreal, Celtic, Lusitanian, Meditteranean and Black Seas) seas. His book about these seas, Natural History of the European Seas (completed after his death by Robert Godwin-Austen), is considered to be the first treatise on marine ecology. He also was the first to consider population dynamics in the sea, and founded the science of paleoecology in a report in which he described the fossil record which might be expected in the Aegean Sea if it were to be elevated or filled with sand. See Hedgpeth (1957c).
where u is the flow velocity, g the gravitational acceleration, and H the fluid depth, and the approximate phase speed of shallow water gravity waves. A Froude number greater than unity is indicative of what is called supercritical flow, and one less than unity of subcritical flow.
When dealing with internal waves, an internal or densimetric Froude number is defined which corresponds to the ordinary Froude number with with the reduced gravity g' replacing g in the above. See Turner (1973) and Houze (1993).