1872.] 



' Shearwater 3 Scientific Researches. 



557 



reduces its Temperature to 30°, and proportionally augments its Specific 

 Gravity, then (the levels of the two columns being equalized by such in- 

 flow) the excess of weight in column C will be maintained, until, by the 

 continued outflow through the bottom pipe, the whole of the warm water 

 in column W has been transferred to C ; for this outflow lowers the level 

 in C, and at the same time tends to lift up the superincumbent warm 

 water in W, which will consequently flow back through the upper pipe 

 into C, so as to restore the equality of the levels of the two columns. And 

 if all the water which passes from W to C is cooled down on entering C, 

 this circulation must continue, though at a gradually diminishing rate, 

 until equilibrium is restored by the depression of the temperature of the 

 entire water of both columns to 30°. — But let us suppose, further, that the 

 cold water, as it enters the bottom of "W by the lower pipe, has its tempera- 

 ture raised again by warmth applied beneath ; and that this elevation is 

 further increased by surface-heat as the water rises to the top of the column ; 

 the result will be that, as the temperature of the water in column W, except 

 of that lowest stratum which has last arrived from C, will be kept con- 

 stantly above that of column C, whilst there will be a constant tendency to 

 the equalization of the levels of the two columns, there will be a continu- 

 ally renewed difference between their Specific Gravities and consequently 

 between their absolute weights. This will produce a continual transference 

 of water from the bottom of C to the bottom of W, and from the top of 

 W to the top of C, with a constant descending movement in C and a con- 

 stant ascending movement in W. The descending movement in column 

 C will not consist in a successional descent of surface-films from above 

 downwards, unless it should happen that the surface-cold is intense enough 

 to reduce their temperature below that of the subjacent water ; but it will 

 be a downward movement of the entire mass, as if water in a tall jar were 

 being drawn off through an orifice at the bottom. And in like manner the 

 upward movement in column W will not so much consist in a successional 

 ascent of bottom-films, as in an upward movement of the entire mass ; since 

 the films warmed at the bottom will only ascend until they meet with water 

 of which the temperature is as high as their own ; and this will be the case 

 so soon as they have passed through the cold stratum which has last 

 flowed in from C. The force which will thus lift up the entire column of 

 water in W, is that which causes the descent of the entire column in C, 

 namely, the excess of Gravity constantly acting in C ; the levels of the two 

 columns, and consequently their heights, being maintained at a constant 

 equality by the free passage of surface-water from W to C. 



30. The whole of Mr. Croll's discussion of this question, however, pro- 

 ceeds upon the assumption that the levels of the Polar and Equatorial 

 columns are not kept at an equality, in consequence of the inadequacy of 

 the excess of level in the Equatorial column to put in motion the interven- 

 ing water ; and that instead of there being an excess of weight in the Polar 

 column, there is a condition of static equilibrium between the two. — 



