644 



On the 'Shearwater* Scientific Researches. 



and line from yielding to the opposite motion of the fluid, as they would 

 have done had the ship been sailing at that rate through the water*. 



177. General Oceanic Circulation. — The animadversions which Capt. 

 Spratt has made upon what he terms " the universal Under-current Theory 

 so fascinatingly advocated by Maury and others, and more recently by the 

 late Dr. Forchhammer," have no real bearing upon the doctrine of a 

 General Oceanic Circulation sustained by differences of Temperature alone, 

 which I have recently been led to advocate. I do not in the least call in 

 question the production of a horizontal circulation by Wind-currents ; on 

 the contrary, I have expressly pointed out, in the case of the Gulf-stream, 

 what I believe to be the mode in which that circulation is completed : 

 and I have no belief that, save under peculiarly exceptional conditions, 

 any thing like a current can be produced by differences of Temperature 

 alone. But to the question how the Temperature-phenomena which I 

 have correlated are to be explained, except upon the supposition of a 

 continual movement of Polar water, however slow, along the Ocean- 

 bottom towards the Equator, involving as its necessary complement a flow 

 of Equatorial water towards the Poles, Capt. Spratt does not seriously 

 address himself; the Temperatures he cites being those collected in the 

 older voyages, to which he has applied a correction of 4°, which is in- 

 adequate whenever it has reference to depths beneath 1200 fathoms. 

 "When the contrast I have drawn in the first part of my present Report 

 between the Temperature-phenomena of Inland Seas, — such as the 

 Mediterranean, the Red Sea, and the Sulu Sea, — with those of the Oceans 

 with which they respectively communicate, shall have been rationally 

 accounted for on any other hypothesis than that of a General Oceanic 

 Circulation, the merits of the two explanations can be fairly discussed. 

 But as such a discussion will be far more satisfactory when that vast mass 

 of additional data shall have been collected which is likely to be furnished 

 by the Scientific Expeditions that are at present either in progress or in 

 preparation, I would suggest the expediency of postponing it until it can 

 be more profitably resumed. At present, as I have already said, I claim 

 for the doctrine of the General Oceanic Circulation no higher a character 

 than that of "a good working hypothesis," consistent with our present 

 knowledge of facts, and therefore entitled to be provisionally adopted for 

 the purpose of stimulating and directing further inquiry. 



* Edinburgh Philosophical Journal, vol. iv. (1821), p. 245. 



