OCEANIC CIRCULATION. 239 



not hold water enough to produce the effects de- 

 scribed by Dr. Carpenter. For in that map the whole 

 area of the Arctic Ocean is presented ; l and from out 

 of that area, be it noted, must come the northern supply 

 of descending water, not only for the Atlantic equatorial 

 current, but for the much larger equatorial current of 

 the Pacific, if Dr. Carpenter's theory be sound. 



The following letter, written by Sir John Herschel 

 only a few weeks before his lamented decease, has been 

 very widely quoted in favour of Dr. Carpenter's theory ; 

 yet if carefully studied it will be found rather to set 

 forth the strength of the theory advocated a year earlier 

 by the present writer. In this letter, at least, Sir John 

 Herschel appears to be disposed, in so far as he con- 

 cedes the efficiency of heat, cold, and evaporation, to 

 incline to the equatorial action as the most important. 

 Answering Dr. Carpenter, who had addressed a letter 

 to him on the subject, he says : ' After well considering 

 all you say, as well as the common-sense of the matter, 

 and the experience of our hot-water circulation pipes 

 in our green-houses, &c., there is no refusing to admit 

 that an oceanic circulation of some sort must arise from 

 mere heat, cold, and evaporation, as verce causce ; and 

 you have brought forward with singular emphasis 2 the 

 more powerful action of the polar cold, or rather, the 



1 The bounding lines drawn from the pole on the right and left of 

 the white space represent one and the same meridian. 



2 In Sir John Herschel's letters one can often recognise slight touches 

 w.e will not say of sarcasm (for he was incapable of saying aught that 

 could be considered bitter or unpleasant), but of what may be described 

 as a humorous suggestiVeness. 



