Theories of Ocean Tides
As studied in the previous sections we now know that tides are nothing but the periodic rise and fall of ocean waters caused primarily by the gravitational forces of the Moon and the Sun, combined with the Earth’s rotation.
Over time, various theories have been proposed to explain tidal behavior. The major theories—Newton’s Equilibrium Theory, Whewell’s Progressive Wave Theory, and Harris’s Stationary Wave Theory—offer different perspectives on how tides are generated, propagated, and influenced by geographical and oceanic factors.
- Newton’s Equilibrium Theory (1687) provides a fundamental understanding of tides based on gravitational forces but assumes an idealized, water-covered Earth.
- Whewell’s Progressive Wave Theory (1883) recognizes the role of landmasses and ocean depths in shaping tidal waves, emphasizing that tides behave like progressive waves moving westward.
- Harris’s Stationary Wave Theory refines the concept further by explaining how oceanic oscillations around central points (amphidromic points) influence regional tidal patterns.
Each of these theories has contributed to our understanding of tides, with modern oceanography integrating elements from all three to explain real-world tidal behavior accurately.
Comparison of Theories of Ocean Tides
| Feature | Newton’s Equilibrium Theory | Whewell’s Progressive Wave Theory | Harris’s Stationary Wave Theory |
| Proposed By | Isaac Newton (1687) | William Whewell (1883) | R.A. Harris (US Coast Survey) |
| Basic Concept | Tides are caused by the Moon and Sun’s gravitational forces, creating two tidal bulges on Earth. | Tides behave like waves moving across oceans, influenced by the Moon’s gravity and obstructed by landmasses. | Tides oscillate around fixed points (amphidromic points), creating rotational tidal movements. |
| Earth’s Assumption | Idealized, water-covered Earth | Real Earth with continents and varying depths | Real Earth with regional oscillations |
| Tidal Movement | Tidal bulges remain fixed with respect to the Moon while Earth rotates beneath them. | Tidal waves move westward due to the Moon’s gravity but are disrupted by continents. | Tides oscillate around amphidromic points rather than moving in a single direction. |
| Role of Landmasses | Not considered | Considered as barriers disrupting tidal waves | Major influence, as they determine tidal oscillations around amphidromic points |
| Tidal Cycle Explanation | Explains two high and two low tides per day but does not account for real-world complexities. | Explains why tides do not occur at the same time along the same longitude. | Explains regional variations and why some areas experience extreme tidal differences. |
| Strengths | Provides a basic gravitational framework for tides. | Recognizes that tides move as progressive waves affected by geography. | Explains localized tidal variations and amphidromic systems. |
| Limitations | Assumes a uniform ocean and does not account for landmasses or ocean depth variations. | Does not fully explain extreme tidal variations in certain coastal regions. | Does not explain deep-sea tidal behavior and ignores bottom topography. |
| Best Application | Theoretical foundation for understanding tides. | Understanding large-scale tidal wave propagation across oceans. | Predicting regional tides and amphidromic tidal behavior. |
Each theory contributes to a better understanding of tides, and modern oceanography integrates their concepts into the Dynamic Theory of Tides, which considers real-world complexities such as ocean currents, seabed topography, and atmospheric influences. Read about these theories in the upcoming sections.
