Forel, Handbuch der Seenkunde: allgemeine Limnologie (Stuttgart, 1901); F.
Forel, " La Limnologie, branche de la geographie," Report VI.
Forel and C. Emery in various Swiss and German periodicals, and especially by C. Janet in his Etudes sur les fourmis, les guepes et les abeilles (Paris, &c., 18 931904).
The northern seas have an increasing tendency towards green, the Irminger Sea showing 5-9 Forel, while in the North Sea the water is usually a pure green (io-14 Forel), the western Mediterranean shows 5-9 Forel, but the eastern is as blue as the open ocean (0-2 Forel).
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