Deductions from the Curve. 41 



perature will remain stationary at or near the level of the 

 obstruction, and the stratum of warm water will extend to the 

 bottom, and thus fill up the whole space between the surface 

 and the bottom, whatever may be the depth of the basin 

 (Plate 16). 



This constant supply of heat and of cold is effected, as is well 

 known, through the agency of currents. The latter are by no 

 means an exceptional phenomenon confined to certain parts of 

 the ocean. Varying in volume and velocity until they attain 

 the proportions of gigantic rivers flowing at a rate of several 

 miles an hour, they occupy every part of the ocean, no part of 

 which can be said to be in a condition of absolute rest. Com- 

 bined together they form, like the currents in the atmosphere, 

 and in intimate association with the latter, a complete system of 

 circulation, by which the physical and chemical equilibrium of 

 the ocean is maintained. From the principal storehouse of heat 

 in the tropics, warm currents proceed towards the temperate 

 and frigid zones, and return thence in the character of cold 

 currents towards the regions of the Equator. That this is so is 

 proved by the results of all observations made up to the present 

 day, and it is in perfect agreement with the well-known agency 

 of water as a storer-up and carrier of heat. 



Two strata of different temperatures cannot remain in con- 

 tact for any time without the formation of an intermediate 

 stratum. This is presumably the reason why a series of deep- 

 sea temperature observations generally assumes the shape of a 

 curve, nowhere presenting a break or an abrupt transition from 

 one temperature to another. The depth of this intermediate 

 stratum will depend upon the duration of the contact. When 

 two masses of water, one warm the other cold, move in different 

 or opposite directions, the intermediate stratum will present a 

 rapid transition from the temperature of one stratum to the 

 temperature of the other, and the part of the curve which 



