Merits:
Newton’s Law of Gravitation laid the foundation stone on which later theories were based. There is no doubt that Newton’s work of gravity made possible the analysis of the tide- generating forces in terms of the effect of the gravitational attraction of the sun and moon on the earth.
The equilibrium tide would be produced on an ideal earth covered with a layer of water of uniform depth, which is not the reality. Even then this tide is of great help in projecting a correct picture of the tide generating forces. The equilibrium tidal theory helps us to understand the periodicity of the tides. Despite many shortcomings the historical importance of this theory cannot be ignored.
Demerits:
ADVERTISEMENTS:
(i) The first and foremost objection raised against the equilibrium theory is that the assumption that the globe is completely covered by water is far from the reality.
(ii) According to this theory, high water of a lunar tide at a particular place should occur when the moon passes through the meridian of that location. But observations have not established this theoretical assumption. In fact, the high tide each day occurs a little later than it was a day before. There is a lag of about 50 minutes. However this delay may vary from place to place.
(iii) Due to the fast propagation of the equilibrium tide on earth, an enormous displacement of water would be necessary to establish the equilibrium position at any instant. Actually the equilibrium position is never achieved.
(iv) The equilibrium theory completely neglects the effect of the continents and land masses which obstruct the free movement of the tidal bulges across the assumed unobstructed ocean surface.
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(v) The ocean basins formed between the continents have set up within each of them free oscillatory waves whose character modifies the forced astronomical tide waves developed in them.
(vi) In certain areas two nearby locations experience high tides at different points of time, the difference being several hours. ‘This fact alone does not prove the validity of the equilibrium theory of tides.
(vii) The difference in the tidal ranges occurring at places along the same meridian is one of the objections raised against this theory.
(viii) The equilibrium theory in its zeal for oversimplification ignored a number of ground realities like the frictional force, the Coriolis force, the bottom relief of the oceans, and the varying depth of ocean water, etc. which affect the movement of tidal waves considerably.