48 Currents of the Ocean. 



of atmospheric circulation composed of equatorial and polar 

 currents ; and by Lieutenant M. F. Maury, that the same 

 inequality must be considered as the primary cause of a system 

 of oceanic circulation also composed of polar and equatorial 

 currents. The two distinguished philosophers have proved that 

 these currents do not flow in the direction of the meridian, since, 

 under the influence of the diurnal rotation of our planet from 

 west to east, polar currents, as they move from a parallel of a 

 lesser to one of a greater rotatory velocity, have a tendency to lag 

 behind and to deviate in a westerly direction, while equatorial 

 currents, in their progress from a lower to a higher latitude, have 

 a tendency to deviate in the direction of the earth's rotation, 

 i.e., towards the east. All observations agree in establishing 

 the fact that the internal economy of the atmosphere and of 

 the ocean is regulated by such a system of circulation composed 

 of equatorial and polar currents, and that the direction of these 

 currents is affected by the earth's diurnal rotation in the manner 

 above described. 



Vertical and Horizontal Extension of the Two Ter- 

 restrial Envelopes. — Before entering upon an examination of 

 the phenomena of atmospheric and oceanic circulation, it is 

 necessary to attach due importance to a condition sometimes 

 overlooked in connection with occurrences which, in their 

 ensemble, embrace immense areas of the surface of our planet — 

 that is, the great disproportion which exists between the depth or 

 vertical extension and the lateral or horizontal extension of the two 

 terrestrial envelopes. The neglect of this condition is probably 

 due to the exaggerated scale which it is necessary to adopt in 

 graphical representations of oceanic and atmospheric sections, 

 and to the difficulty of placing before our mental vision 

 phenomena of such colossal proportions as we find realised in 

 the great currents of the air and of the sea. 



The average depth of the ocean, whether we estimate it at 



