228 



M. L. FULLER — THE SEA MILLS OF CEPHALONIA 



latter may not be considerably longer, as would naturally be the case if 

 derived from the highlands of the mainland. This point is brought out 

 by figure 3, which shows a circulatory system in which F is the fresh 

 is presiimably derived, and S, the silts which prevent communication with 

 the sea.* In order that the salt water may commingle with the fresh, it 

 must have, as |ust indicated, a weight at least equal to that of the fresh 

 water, although this does not mean that the length of the column of the 



Figure 2. — Diagram sJioiving supposed Conditions of Circulation at the Sea Mills of 



Cephalonia. 



water column, 103 feet in height and rising 3 feet above the salt water 

 inlet; S, the salt water column, 100 feet in height, and M, the mixed 

 column. Under such conditions the waters would mix in equal propor- 

 tions (50 per cent dilution of the salt water), giving to the outlet column 

 (M) a head of 1% feet, or more than enough to establish the conditions 

 essential for circulation. With a salt column 1,000 feet in height, the 

 fresh column would be 1,030 feet and the mixed 1,015 feet in height. 

 If the fresh water column is of greater weight than the salt water col- 



FiGTiRB 3. — Conditions of Head in Circulation System with fresh (F), salt (S), 



mixed (M) Columns. 



and 



umn, the water of the latter will be forced back and a spring result. If, 

 however, the salt water column is heavier than the fresh water, the latter, 

 having no outlet, will tend to rise until its pressure so nearly approaches 

 that of the salt water column that intermixture begins. Once started, 

 the circulation is facilitated l^y the lower density of the resulting mixture, 



* In order to show the supposed conditions by a single section, certain generalizations 

 were necessary. In reality M, P, and SM are not in a straight line, the direction from 

 M to P being southeast and northwest, while that from P (Argostoli) to SM (at the 

 northern end of the peninsula) is considerably. more northerly. 



