SOME PROBLEMS OF THE SEA. 7 



is shaped in accordance with, mathematical formulse to 

 ensure the most efficient proportions. They have 

 calculated filtration co-efficients applicable to each kind 

 of silk employed, in its various conditions. They have 

 elaborated apparatus for filtering, measuring and 

 analysing the results of the catch. They have made 

 series of observations in fresh-water lakes and in some 

 parts of the ocean, and from the samples so obtained 

 they have drawn conclusions as to the population and the 

 cyclical changes of matter in the sea of a very wide- 

 reaching nature. 



Dr. J. Travis Jenkins, some five years ago, gave an 

 account to this Society of the " plankton " work as carried 

 out by the Germans in the North Sea and the Baltic, 

 and on that occasion he said : — " It is to be hoped that 

 the Irish Sea may be subsequently investigated in like 

 manner. A comparison with the results already obtained 

 from the North and Baltic Seas could not fail to be of 

 interest and to yield important results." (Trans. L.B.S., 

 Vol. XV., p. 280.) For several years I have been trying 

 to get such work carried out in connection with our 

 local sea-fisheries investigations ; but, although everyone 

 concerned is sympathetic and helpful, it is difficult to get 

 any new work, however important, undertaken on board 

 a steamer that cannot, because of administrative duties, 

 be wholly devoted to scientific investigation. A Hensen 

 plankton net has now been obtained for the fisheries 

 steamer, but is not yet being systematically used. It was 

 partly because of this difficulty that I decided to charter 

 a small steamer myself for a couple of ' months this 

 summer and then made the series of trials of plankton 

 nets at Port Erin which I shall tell you about presently. 



But let me first give you some idea of the problems 

 in the economics of the sea, which Hensen and his fellow- 



