THE OCEAN FEEDING-GROUNDS 75 



its temperature in situ of 9 degrees. 1 The litre of sea- 

 water thus understood is not an inert quantity, but an 

 active, indeed, I had almost said a living, thing, obey- 

 ing Marsigli's law, which is formulated thus. Sea- 

 waters travel from layers having a low nS 4 towards 

 levels having a high wS 4 . I must ask the reader to 

 pardon me for giving a somewhat obscure explanation, 

 but I cannot otherwise explain the properties of which 

 I have to speak. 



Thanks to this law, which he has developed and 

 elucidated, M. Thoulet has been able to achieve the 

 synthesis of oceanic circulation. The liquid mass of 

 the ocean is divided horizontally into two superimposed 

 regions ; one contained between the surface and a super- 

 ficies about five hundred fathoms below the surface, 

 in which the circulation of the waters takes place with 

 a maximum of activity ; and one contained between 

 the said superficies and the bottom, in which, except 

 in rare and even doubtful instances, there is no circu- 

 lation whatever. In the first region the currents, at 

 any one point or along any one line, may vary in 

 direction and in intensity. Moreover, while on the 

 subaerian soil all currents of water flow down their 

 inclined beds, submarine currents flow upwards from 

 the lower regions of their beds. Evaporation being 

 more active at the equator than at the poles, the waters 

 advance from the poles towards the equator. The 

 thickness of the liquid layer evaporated at any one 



1 The unit of volume of sea-water, the litre, at the fixed tempera- 

 ture of zero Cent, or 32 Fahr., has a certain weight, variable in 

 various specimens, according to the quantity of salts in solution, and 

 which, evaluated by reference to the weight of the litre of distilled 

 water at the temperature +4 Cent., which is that of its maximum 

 density, is the absolute density, S 4 , of the specimen. 



