PREFACE vii 



Modern oceanographical research has been developed from the 

 work of Murray, Buchanan and Dittmar, which was based on the 

 collections and observations made during the Challenger expedi- 

 tion. Cleve and Pettersson then attempted to trace the origin of 

 the water which, from season to season, drifted to the shores of 

 Scandinavia. Knowing that different sea-areas were characterised 

 by different /aczes of microscopic life they endeavoured to press the 

 study of the plankton into the service of hydrography, and 

 hydrography into that of meteorology. Like Hensen's, their 

 object was a restricted one, but the idea involved was so fruitful 

 that a host of investigations sprang from it. To it we owe new 

 determinations of the chemical composition, and the physical 

 properties of sea water ; and the invention of beautiful apparatus 

 for the tracing and measurement of ocean currents ; as well as the 

 mathematical investigations by Sandstrom, Helland-Hansen, and 

 D'Arcy Thompson of the movements of water-masses in the sea. 

 Then if different plankton types are to be associated with water of 

 different chemical and physical properties the causes are to be 

 sought. Again new investigations were instituted, and the study of 

 the association of changes in the salinity and temperature of the 

 sea, with concomitant changes in the nature and abundance of the 

 plankton, was extended to the study of the migrations and breed- 

 ing habits of fishes. Queer side-issues have arisen in the course 

 of these investigations : the study of the physical condition of the 

 particles composing the sea-bottom, for instance, and the association 

 of changes in the viscosity of the sea water with the movements 

 of the plankton. 



Possibly more was anticipated from the direct results of the 

 quantitative investigation of the plankton than has actually been 

 acquired. Probably too, Hensen, Cleve and Pettersson under-rated 

 the difficulties of the work, and under-estimated or overlooked 

 sources of error. It would be strange indeed if they did not ! 

 Criticism, both of methods and results, has not been wanting. 

 How much, for instance, has the quantitative study of marine life 



