96 Mr. J. Croll on the Physical Cause of Ocean- currents. 



assumes to exist. I have also considered more in detail what 

 seem to me to be the radical defects of his theory, and have again 

 reviewed some matters regarding which he appears to have 

 slightly misapprehended the drift of my argument. It was 

 shown on a former occasion that, if the heat received by the ocean 

 in intertropical regions were distributed over the globe, not by 

 currents produced by the wind, but by means of a circulation due 

 to difference of temperature between equatorial and polar waters, 

 then there could be no secular changes of climate resulting from 

 variations in the eccentricity of the earth's orbit— because such 

 a mode of circulation would, as I have shown, tend to neutralize 

 the effects which would otherwise result from an increase of 

 eccentricity. For this reason I have been the more anxious to 

 prove that intertropical heat is conveyed to temperate and polar 

 regions by ocean-currents, and not by means of any general 

 movement of the ocean resulting from difference of gravity. I 

 have therefore on this account entered more fully into that part 

 of the subject than I otherwise would have done. Irrespective 

 of all this, however, the important nature of the whole question, 

 and the very general interest it excites, may be regarded as suf- 

 ficient excuse for the length of the present communication. 

 Circumstances over which I had no control have delayed its 

 publication for nearly a year. 



The Facts and their Explanation. 



" I have thought it desirable/' says Dr. Carpenter, " to deve- 

 lope somewhat at length what I regard as the bearings of the 

 results obtained by these inquiries upon the doctrine of a general 



oceanic circulation sustained by difference of temperature 



As no similarly comprehensive examination has been made, so 

 far as I am aware, by any other scientific inquirer, and as the 

 doctrine put. forth on the subject by Mr. Croll is likely, if not 

 thus scrutinized, to command the unquestioning assent of those 

 who regard him as a high authority on the subject of oceanic 

 currents and their bearings on geological questions, I venture 

 to hope that the conclusion of its results as an appendix to this 

 Report will not be deemed inappropriate" (p. 538). 



The Facts to be explained. — He then commences by giving a 

 restatement of the facts for the explanation of which his theory of 

 a general oceanic circulation has been advanced. It is well known 

 that, wherever temperature-observations have been made in the 

 Atlantic, the bottom of that ocean has been found to be occupied by 

 water of an ice-cold temperature. And this holds true not merely 

 of the Atlantic, but also of the ocean in intertropical regions — a 

 fact which has been proved by repeated observations, and more 

 particularly of late by those of Commander Chimmo in the China 



