58 Scientific Intelligence. 



former are complimentary to those of the latter. In other words 

 the bright portions of one set correspond to the dark parts of the 

 other. — Jourit. de Phys., iv, 209, k. c. p. 



13. The Wind Theory of Oceanic Circulation. Object torn 

 examhied ; by James Ceoll, of H. M, Geological Survey of Scot- 

 land. (From the Philoso]>hical Magazine for October, 1 875).*— 

 The fundamental argume)ds of the advocates of the gravitation 

 theory. — 1. The gravitation theorists base their argument on two 

 principal assumptions which cannot be conceded. First, they 

 maintain that the existence of polar water in the depths of the 

 ocean is consistent with their theory only ; and, secondly, they 

 assume as a necessary condition of the wind theory that the 

 understratum of the ocean should consist of warm water. It is 

 a well recognized fact that the ocean beyond the reach of sun heat 

 is occupied with water of a polar temperature ; and they therefore 

 point triumphantly to the fact as at once a proof of their position 

 and a conclusive argument against the wind theory. But, on the 

 other side, it will not be difficult to show that the existence of 

 cold water throughout the ocean depths is as much a necessary 

 result of the wind theory as of the gravitation theory, and that 

 there is no relation whatever between the wind theory and warm 

 water m the depths of the sea. 



It is supposed that the return ta tder-cwrents from the polar 

 regions are by far too insignificant to be able to maintain at a 

 polar temperature the great depths of the ocean. 



Let us examine tliis objection. It is freely admitted, nay even 

 strenuously maintained by the advocates of the gravitation theory 

 themselves, that the heating-power of the sun does not extend to 

 any great depth below the surface of the ocean ; consequently 

 there is nothing Avhatever to heat this mass of water underneath 

 except the heat coming through the earth's crust ; but the amount 

 of heat derived from this source is so trifling that an under-current 

 from the Arctic regions of no great magnitude would be sufficient 

 to keep the mass at an ice-cold temperature. 



On a former occasion f I showed that, taking tlie rate at which 

 internal heat passes through the earth's surface to be that assigTicd 

 by Sir William Thomson, the total amount received per annum l»y 

 the North Atlantic, between the equator and tropic of Cancer, 

 including the Caribbean Sea, is equal to only ^^ of that conveyed 

 by the Gulf-stream, on the supposition that each pound of water 

 carries 19,300 foot-pounds of heat,— and that consequently an 

 under-current from the polar regions of not more than 5^ the 

 volume of the Gulf-stream would sufiice to keep the entire mass 

 of water of that area within 1° of what it would be were no heat 

 derived from the crust of the earth, and an under-current of less 

 than yV tliat of the Gulf-stream coming from the polar regions 

 would keep the entire North Atlantic from the equator to the 

 arctic circle filled with ice-cold water. A polar under-current half 



