Archive image from page 68 of The depths of the ocean;. The depths of the ocean; a general account of the modern science of oceanography based largely on the scientific researches of the Norwegian steamer Michael Sars in the North Atlantic depthsofoceange00murr Year: 1912 THE SHIP AND ITS EQUIPMENT 37 he generally uses sackcloth, but a better fine-meshed material would undoubtedly be more desirable. Hensen evolved various forms of apparatus for a quantitative study of the pelagic organisms, that is to say, for estimating the relative amounts of plankton organisms present in a given volume of
Archive image from page 68 of The depths of the ocean;. The depths of the ocean; a general account of the modern science of oceanography based largely on the scientific researches of the Norwegian steamer Michael Sars in the North Atlantic depthsofoceange00murr Year: 1912 THE SHIP AND ITS EQUIPMENT 37 he generally uses sackcloth, but a better fine-meshed material would undoubtedly be more desirable. Hensen evolved various forms of apparatus for a quantitative study of the pelagic organisms, that is to say, for estimating the relative amounts of plankton organisms present in a given volume of water. He recommends vertical nets of the finest silk cloth, such as is used in the milling industry (see Chapter VI.). In actual practice, however, it has been found impossible to capture pelagic organisms of every sort with the same net; for the larger forms may escape the net altogether, while the smallest forms may pass through the meshes of even the finest silk. There are other objec- tions to the method, for it is an almost impossible task to ascertain the total quantity of floating organisms in deep and shallow water where there are strong currents ; and it is hardly likely that the larger organisms at any rate, even though the nets succeed in cap- turing them, are uniformly distributed throughout the water-masses over large areas, so that an estimation of their total number could not be arrived at with our present appliances. Still, Hensen Hensen's theoretical analysis of plank- Plankton net- ton problems has been of great service to oceanic research, and so, too, has his plankton net (Fig. 19), whose co- efficient of capture naturalists have attempted to calculate. It has been of the utmost value, for instance, in investigating certain uni- formly distributed minute species in less extensive areas. The apparatus consists of a filtration net of miller-silk, with a brass cylinder at the lower end of the net, and a large conical part made of canvas, the object of which is
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