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 sufficient 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 Christiania, formerly head of the splendid Norwegian oceanographic expedition of the Vöringen, 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.). According 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
- ↑ H. Mohn. The Temperature of the Sea, and the Fish in the Loffoten. Christiania, 1889.
