360 Dr. Carpenter on the Physical Cause of Ocean-currents. 



miles per day ; the average of the six months of most rapid rate 

 is 60*6 miles per day. 



Further, as the maximum rate given by the Meteorological De- 

 partment is 106 miles per day, and as this rests on only a 

 single observation, it is obvious that the Admiralty maximum of 

 120 miles per day is a case as exceptional as that of a man who 

 has twenty children by one wife. 



The annual mean assumed by Mr. CrolJ, on the basis of the 

 maximum and minimum rates, thus exceeds the very highest 

 actual monthly average, and is more than double the monthly 

 average of half the year ; whilst the annual mean stated by 

 me, on the express authority of the Meteorological Department, 

 is the average of all the observations in its possession. 



The foregoing case furnishes a typical example of the arith- 

 metical method on which Mr. Croli relies, in his laboured dis- 

 proof of the doctrine of a Vertical Oceanic Circulation sustained 

 by Thermal Agency alone, which has received the full sanction, 

 on theoretical grounds, of numerous eminent Physicists (as, for 

 example, of Sir George Airy, in his Presidential Address to the 

 Royal Society in 187.2), and which appears to the French Aca- 

 demicians before whom I recently brought it (Comptes Rendus, 

 April 6), to be in entire harmony with the facts of Ocean-tem- 

 perature as determined by the ' Challenger ' observations. 



But, further, Mr. Croll asserts (p. 99) that " all we really 

 require to account for the cold water which is found to occupy 

 the bed of the ocean in temperate and equatorial regions," is a 

 set of polar under-currents maintained by the winds which im- 

 pel equatorial water towards the poles; and further (p. 175), 

 that, " so far as the distribution of heat over the globe is con- 

 cerned, it is a matter of indifference whether there really is or is 

 not such a thing as this general oceanic circulation. The enor- 

 mous amount of heat conveyed by the Gulf-stream alone puts 

 it beyond all doubt that ocean-currents are the great agents 

 employed in distributing over the globe the excess of heat re- 

 ceived by the sea in intertropical regions." 



Regarding the facts of the case as better data than Mr. CrolPs 

 figures, I would submit whether the following considerations do 

 not furnish a reductio ad absurdum of the foregoing statements: — 



1. In the Equatorial Atlantic, as is shown by the 'Challenger' 

 sections, the whole mass of water, from 300 fathoms to the bot- 

 tom at (say) 2500 fathoms, has a temperature descending from 

 40° to 32°. The isocheimenal of the Equatorial Atlantic (which, 

 as is shown by the temperature-phenomena of the Mediterranean 

 and Red Sea, would be the temperature of all but the superficial 

 stratum throughout the year, if Polar water were excluded) is 

 about 75°. Hence it is clear that the great bulk of this water 

 must have travelled to the Equator from the Polar areas. That 



