OCEANOGRAPHY. 413 



special kind of bottom and currents of calculable speed. All these details 

 are implied in the presence or absence of this fish. Fishing is a problem 

 which consists in knowing beforehand whether in such a place at such and 

 such a time the fish will be abundant, rare, or absent. Other nations 

 have fully recognized that the study of fisheries is, above everything, 

 the study of the relations existing between the marine environment 

 and the animal ; that is to say, a question of zoology whose first basis 

 is knowledge of the environment, which is a question of oceanography. 

 They have put the principle in practice in their laboratories and in 

 their official administrations, working out in detail the oceanography 

 of a region before devoting themselves to zoological researches there. 

 It is to be wished that this practice were more generally followed. It 

 is a common sense law, but it is only too true that such are the slowest 

 in making themselves known. Every improvement is simplification, 

 and the men who cry unceasingly for simplicity are as if appalled when 

 they come upon it unawares. 



But if the presence or absence of a fish is so difficult to determine 

 except by long and expensive trials, it is not so with the condition of 

 the environment, which can be estimated and even recorded in figures, 

 by means of instruments; temperature by the thermometer, density 

 and salinity by the areometer, depth by the sounding line, the nature 

 of the bottom by a lithological or chemical analysis. The instrument 

 offers the advantage of having a perfect graduation, recording a suffi- 

 cient number of degrees and consequently great delicacy of indication. 

 On the other hand, it has the inconvenience of recording but one of the 

 conditions of the surrounding of which the living creature records the 

 whole. However, we must not forget that the purpose of science is, 

 briefly, to discover what is above all others the most essential influence, 

 and besides that if a single instrument is not sufficient, there is nothing 

 to prevent our having recourse to many in succession. It would cost 

 the fisher less time and trouble to measure the temperature and then, 

 if it is necessary, the transparency and even the density in a certain 

 region, then according to the results obtained set to work fishing with 

 great probabilities of success, or to immediately leave the ground, than 

 to cast his line and nets into the water, throwing his bait away hap- 

 hazard, to learn finally only after a prolonged trial that the fish will or 

 will not bite. Prof. H. Mohn, of Ohristiauia, formerly head of the 

 splendid Norwegian oceanographic expedition of the Voringen,in 1876, 

 found out 1 that at the Loffoten Islands the cod remained always in a 

 bed of water between 1° and 5° in temperature (39° to 41° F.). Accord- 

 ing to his instructions a Government vessel, commanded by Lieut. G. 

 Gade, went to ascertain the position in depth of this bed and to verify 

 the scientific previsions. The success of this examination was perfect, 

 and now Norwegian fishermen use the thermometer as a fishing 



1 H. Mohn. The Temperature of the Sea, and the Fiah in the Loffoten. Christiania, 

 1889. 



