250 LIGHT SCIENCE FOR LEISURE HOURS. 



that if the removal of equatorial water draws in polar 

 water from the bottom, the whole intermediate stratum 

 should first rise towards the surface. I do not hold 

 the view thus demolished, but simply that the inflow 

 is from below. The question whether the inflow would 

 be from above or below was dealt with by me in a 

 paper on c Oceanic Circulation' in the Student for 

 July 1868. I do not urge this as a proof that Dr. 

 Carpenter's objection is invalid. My reasoning may 

 admit of being refuted. But I wish to show that the 

 objection is not a new one to me. The inflow may be 

 from below without being from the bottom. If it were 

 from the bottom it would not have the effects I have 

 ascribed to it, that is, it would not result in a west- 

 wardly-flowing current. What I conceive is that since 

 the whole tropical and equatorial area is a region of 

 excessive evaporation (as surely no physicist will deny), 

 there is over the whole region a depression of the ocean 

 level. This depression may be, or rather must be, 

 exceedingly minute ; but the total quantity of water 

 thus, as it were, wanting, must be enormous. The 

 difference must by the laws of fluid equilibrium be 

 supplied, and though the immediate supply in equa- 

 torial regions may come from tropical regions, the 

 actual source of the total supply must be sought for in 

 higher latitudes. That the water drawn in under these 

 circumstances would traverse the surface of the Atlan- 

 tic, is by no means proved by the fact that the eminent 

 mathematicians cited by Dr. Carpenter consider that 

 an in-draught to replace water ; swept off from the 



