Mr. J. Croll on the Physical Cause of Ocean-currents. 115 



of account altogether, — polar cold being the primum mobile of 

 the circulation. It is supposed also that I have considered the 

 efficiency of one of the agents, viz. heat, and found it totally in- 

 adequate to produce the circulation in question ; and it is ad- 

 mitted also that my conclusions are perfectly correct. But then 

 I am supposed to have left out of account the other agent, viz. 

 polar cold, the only agent possessing real potency. Had I 

 taken into account polar cold, it is supposed that I should have 

 found at once a cause perfectly adequate to produce the re- 

 quired effect. 



This is a fair statement of Dr. Carpenter's views on the sub- 

 ject ; I am unable, at least, to attach any other meaning to his 

 words. And I have no doubt they are also the views which have 

 been adopted by those who have accepted his theory. 



It must be sufficiently evident from what has already been 

 stated, that the notion of there being two separate agents at 

 work producing circulation, namely heat and cold, the one of 

 which is assumed to have much more potency than the other, 

 is not only opposed to the views entertained by physicists, but 

 is also wholly irreconcilable with the ordinary principles of me- 

 chanics. But more than this, if we analyze the subject a little 

 so as to remove some of the confusion of ideas which besets it, 

 we shall find that these views are irreconcilable with even Dr. 

 Carpenter's own explanation of the cause of the general oceanic 

 circulation. 



Cold and heat, considered as sensations, are very different 

 things ; but cold considered as a condition of a body means 

 only a deficiency or absence of heat. When we say, for ex- 

 ample, that the polar seas are colder than the equatorial, our 

 meaning is that the polar seas possess less heat than the equa- 

 torial. And when we say that the equatorial seas are hotter 

 than the polar, our meaning of course likewise is that the equa- 

 torial seas possess more heat than the polar. Or if we say that 

 the equatorial seas are hot and the polar seas cold, we mean 

 simply that both seas possess a certain amount of heat, the 

 equatorial seas having more than the polar ; or, judging them 

 by our sensations, we call the one hot and the other cold. 



How, then, according to Dr. Carpenter, does polar cold im- 

 part motion to the water ? The warm water flowing in upon 

 the polar column becomes chilled by cold, but it is not cooled 

 below that of the water underneath ; for, according to Dr. Car- 

 penter, the ocean in polar regions is as cold and as dense under- 

 neath as at the surface. The cooled surface-water does not sink 

 through the water underneath, like the surface-water of a pond 

 chilled during a frosty night. "The descending motion in 

 column C will not consist," he says, "in a succession al descent 



12 



