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



and Weyprecht near Spitzbergen) at no great depth beneath the 

 surface, and that instead of rising at still greater depths, the 

 thermometer will fall to near the freezing-point of salt water ,; 

 (§39). 



Dr. Carpenter can hardly claim this as evidence in favour of 

 his theory ; for near the borders of the ice-barrier the water, as 

 a matter of course, could not be expected to have a much higher 

 temperature than the ice itself. And if the observations be made 

 during summer months, the temperature of the water at the 

 surface will no doubt be found to be higher than that of the 

 bottom; but if they be carried on during winter, the surface- 

 temperature will doubtless be found to be as low as the bottom- 

 temperature. These are results which do not depend upon any 

 particular theory of oceanic circulation. 



" The bottom- temperature of the North Pacific," he continues, 

 " will afford a crucial test of the truth of the doctrine. For since 

 the sole communication of this vast oceanic area with the Arctic 

 basin is a strait so shallow as only to permit an inflow of warm 

 surface-water, its deep cold stratum must be entirely derived 

 from the Antarctic area ; and if its bottom-temperature is not 

 actually higher than that of the South Pacific, the glacial stra- 

 tum ought to be found at a greater depth north of the equator 

 than south of it" (§ 39). 



This may probably show that the water came from the Ant- 

 arctic regions, but cannot possibly prove that it came in the 

 manner which he supposes. 



" In the North Atlantic, again, the comparative limitation of 

 communication with the Arctic area may be expected to prevent 

 its bottom-temperature from being reduced as low as that of the 

 Southern Atlantic" (§39). Supposing the bottom-temperature 

 of the South Atlantic should be found to be lower than the 

 bottom-temperature of the North Atlantic, this fact will be 

 just as consistent with the theory of under currents as with his 

 theory of a general movement of the ocean. Indeed I fear that 

 even although Dr. Carpenter's expectations should eventually 

 be realized in the results of the Circumnavigation Expedition, yet 

 the advocates of the wind theory will still remain unconverted. 

 In fact the Director of this Expedition has already, on the wind 

 theory, offered an explanation of nearly all the phenomena on 

 which Dr. Carpenter relies*; and the same has also been done 

 by Dr. Petermannj-, who, as is well known, is equally opposed 

 to Dr. Carpenter's theory. Dr. Carpenter directs attention to 

 the necessity of examining the broad and deep channel separating 



* "Depths of the Sea." 'Nature' for July 28, 1870. 

 t "Memoir on the Gulf- stream," Gcographische Mittheilungen for 

 vol. xvi. (1870). 



