In Figure 2 the oblique lines are isosteres which have been formed 

 by the intersection of the vertical plane of the section with the 

 isosteric siufaces running through the water mass. The space 

 between any two isosteric surfaces is called an isosteric sheet. The 

 uppermost isosteric sheet on the left-hand side of Figure 2, in wedge- 

 shaped form, bounds the body of lightest water that has accumu- 

 lated against the coast. Now the water in the deepest portion of this 

 isosteric sheet ''A" is specifically lighter than the water at the same 

 level in any of the other isosteric sheets, so according to the Archi- 

 median principle this portion of sheet "A" will tend to be driven 

 bodily upwards. The water in the highest portion of sheet ''B" is 

 specifically heavier than the water at the same level of the inshore 

 sheet, and thus it will be dragged downwards. It is plain to see that 



Fig. 2. — A vertical profile of a water mass showing a distribution of light and heavy 

 water and dynamic tendencies which would prevail in such a state 



there are forces tending to turn all the isosteric sheets into a hori- 

 zontal position, and the greater the obliquity of the isosteric surfaces 

 the greater the forces tending toward the leveling process. The 

 water particles themselves, however, as a result of these stresses, 

 will be forced from the thicker portion of the isosteric sheet to the 

 thinner portion of it, the particles tending to keep, for reasons as 

 pointed out in a previous paragraph, wholly within their own re- 

 spective layer. When the sheets have attained a mean uniform thick- 

 ness, then the isosteric surfaces have resumed the horizontal, dynamic 

 equilibrium is established and circulation ceases. 



The causes provoking currents were divided, it will be recalled, as 

 being due to two classes of forces — viz, internal and external. The 

 distinction between the two rests mainly on the manner in which 

 energy is transmitted to the sea. This conception should be clearly 

 understood. 



(1) Internal class of forces refers to those agencies, the effects from 

 which appear forthwith to alter the internal character of the water 

 mass itself. This results in varying the distribution of density. 



