Dr. CrolVs Theory of Glacial and Warm Periods. y$ 



tracts the water, increases its specific gravity, and lowers its 

 level as compared with the water in the equatorial region. 

 To make this good a surface flow sets in towards the former. 

 But in restoring the level the additional water disturbs the 

 equilibrium of pressure, and the column of polar water 

 becomes heavier than that of the equatorial water, 

 "whereby," to use his own words, "a portion of its heavy 

 bottom water is displaced laterally, causing a further 

 reduction of level; which draws in a further supply of the 

 .warmer and lighter water flowing towards its surface, so 

 that the entire column of polar water may be said to be in 

 a state of constant descent, like that which exists in the 

 water of a tall jar when an opening is made at the bottom, 

 and the water which flows away through it is replaced by 

 an equivalent supply poured into the top of the jar." 



In the first place, Dr. Carpenter ignores the difference 

 of density caused by saltness, which compensates very 

 largely, if not entirely, for that created by heat, and 

 makes it far from improbable that there is no differ- 

 ence in specific gravity between water from the equator 

 and the poles, a view in which Professor Wyville 

 Thomson concurs {Climate and Time, 129.) Let this 

 pass, however, and let us turn to the problem as he puts 

 it, and try and measure the amount of pressure, and, 

 consequently, of movement, which can be got out of 

 Dr. Carpenter's primum mobile, the arctic cold. He seems 

 to argue as if the pressure at the base of the polar sea, 

 which, according to his theory, squeezes out its lowest 

 layers, and causes the water to begin to circulate, is to be 

 measured by the whole height of the polar column of water. 

 This is by no means the case. So long as the ocean is in 

 equilibrium the column of polar water exactly balances the 

 column of equatorial water, and all the pressure it can 

 exercise is exhausted in balancing the column of water at 

 the equator. When the equilibrium is disturbed, the amount 



