558 



Dr. W. B. Carpenter on the 



[June 13, 



Having shown the untenableness of this assumption (§ 22), I might dismiss 

 his arguments without further notice, were it not that I should leave it in his 

 power to reply that, granting my view of the case to be the correct one, 

 the force of Gravity which I regard as the primum mobile of the Circulation 

 cannot be greater than it is on his. 



31. In order to show how a disturbance of Static Equilibrium produced 

 by difference of Temperature would operate through a vast extent of 

 Ocean, I shall suppose an elongated Inland Sea like the Mediterranean, 

 with a uniform temperature of 54° throughout, to have one- tenth of its 

 length cut off from the rest by a septum, and the whole surface of this 

 portion to be acted on by Polar Cold, until the temperature of the entire 

 body of water it contains should be reduced to 2/° ; its level being thus 

 lowered, and its Specific Gravity augmented, without any increase in its 

 absolute weight. If, now, we suppose the septum to be removed, it is 

 evident that not only will the depression of level produce a surface-inflow 

 into the Cold area, from the portion of the basin next adjacent to it, but 

 that the compensatory movement must extend, though in a gradually 

 diminishing ratio, to the opposite extremity of the basin : for, if it do not, 

 either water is not a liquid, or liquids do not find their own level. The 

 water of the Cold area, having its surface now raised to the general level 

 of the basin, will have its absolute weight augmented in proportion to its 

 increase in density ; and both its downward and its lateral pressure will 

 therefore be in excess of that of every other column of equal height and 

 base in the entire basin. Now Mr. Croll's position is, that the difference 

 in Gravity between the two columns A and Z at the opposite ends of the 

 basin is a force too small to give motion to the whole intermediate series of 

 columns (B to Y) ; which is equivalent to saying that the heavier water in 

 column A will be permanently banked up by the resistance of columns B 

 to Z ; so that the state of disturbed Equilibrium produced by the original 

 reduction of Temperature will last so long as that reduction is maintained. 



32. Now as such a position is inconsistent, not merely with the theore- 

 tical conception of a liquid, but with facts capable of being verified by 

 daily observation, there must obviously be a fallacy somewhere : and this 

 fallacy seems to me to lie in Mr. Croll's treatment of the whole mass of 

 water en bloc, as if it were a solid body ; instead of regarding it as a liquid, 

 of which each component part, being free to move upon every other (re- 

 tarded only by its "viscosity"), carries from point to point along the whole 

 length of the basin the action of the force initiated at the cold end. In 

 order to determine how this force will operate, we must begin by considering 

 what change will occur between the water of the cold and heavy column 

 (A), and that of the warmer and lighter column (B) next adjacent to it, 

 when free communication has been opened between them. The difference 

 in the weight of the two columns involves an excess of lateral pressure in 

 column A, increasing from above downwards ; and this will cause a bottom 

 outflow of the heavier stratum from A to B, which, by lowering the level 



