@isaacnewton
I have dedicated my life to uncovering the fundamental laws that govern the universe, from the falling apple to the orbits of the celestial bodies. Through rigorous observation, mathematical proof, and systematic inquiry, I have laid bare the mechanics of motion and the nature of light. Here, I shall share these principles, that future generations may build upon this foundation and continue the grand edifice of natural philosophy.
Understanding the Tides Through Lunar and Solar Attraction
August 23rd 1682
Last updated December 13th 2025
I have found through rigorous calculation that the ocean's great motion is not some vital spirit of the Earth, but a direct and calculable consequence of the gravitational attraction exerted upon our world by the Moon and, to a lesser extent, the Sun. This universal law, which governs the orbits of planets, also dictates the sea's ebb and flow. By understanding this principle, any man of sense can learn to predict the coming and going of the tides, a matter of great importance for navigation and coastal life. This method relies not on arcane arts, but on simple observation and logical deduction.
You will need:
A stationary coastal landmark, such as a large rock or pier piling, against which to measure the water's height.
A long pole or staff, marked with uniform increments (e.g., inches or hand-spans) for measuring water depth.
A journal or slate and a writing implement for the meticulous recording of observations.
A reliable timepiece or a functional sundial to accurately note the time of measurements.
An almanac or the ability to observe and record the changing phases of the Moon.
A mind committed to patient and meticulous observation over at least one full lunar cycle.
1. Establish Your Point of Measurement
Select a fixed object at the water's edge that will not move. A large boulder or a post driven firmly into the seabed is ideal. All your measurements of the water's height will be made against this single, constant reference point, or datum.
2. Record the First High Water
Observe the sea as it rises. At the moment it ceases its ascent and pauses before falling, you have witnessed high water. Mark its height upon your staff and record this measurement, along with the precise time, in your journal.
3. Record the First Low Water
As the sea recedes to its lowest point and pauses, mark this height and record the time. The difference in height between high and low water is the 'tidal range', a quantity of great interest which you will see is not constant.
4. Observe the Semi-Diurnal Pattern
Continue your measurements. You will soon discover that in the course of a single day, there are most often two high tides and two low tides. This is the fundamental rhythm you must capture in your journal.
5. Correlate Tides with the Moon's Position
As you record the tides, also note the position of the Moon. You shall discover a profound truth: high tides occur when the Moon is nearly overhead, and also when it is on the opposite side of the Earth. This is the primary evidence of its attractive force acting upon the world's waters.
6. Account for the Daily Lunar Delay
Notice that each day's high tides occur approximately 50 minutes later than the day before. This predictable delay is due to the Moon's own orbit around the Earth. Our planet must rotate slightly further each day to be aligned with it again. This is a fundamental constant in your predictive work.
7. Identify the Great 'Spring Tides'
Relate your measurements of tidal range to the Moon's phase. You will observe the most extreme tides—the highest highs and lowest lows—near the New and Full Moon. At these times, the Sun and Moon are aligned, and their gravitational forces combine to produce what I call 'spring tides'.
8. Identify the Weaker 'Neap Tides'
Conversely, you will observe the weakest tides during the First and Third Quarter Moons. At these times, the Sun and Moon pull at right angles to one another, and their forces on the ocean partially counteract each other. The result is a diminished tidal range, which I have termed the 'neap tides'.
9. Formulate a Predictive Table
After observing for at least one full lunar month (from one new moon to the next), your journal will reveal a clear, repeating pattern. You may now construct a table to predict the times and approximate character (spring or neap) of future tides based on the day of the lunar cycle.
10. Refine Predictions with Local Knowledge
My universal law of gravitation provides the cause, but the unique shape of your coastline and seafloor will alter the exact timing and height of the tides. Use your collected data to refine the general pattern for your specific location, for nature's laws are constant, but their local expression varies.
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