(Published in the Philippine Daily Inquirer, August 13, 2005, p. A15.)
NOW, EVEN grade school pupils can explain that high and low tides of the sea are caused by the gravitational pull of the moon.
And some calendars freely given out by business establishments at yearend include phases of the moon and measurements of seawater levels on specific days of the year.
But how did mankind reckon with the mystery of the ebbing and rising of ocean tides before Sir Isaac Newton discovered gravitation as a scientific law?
In 1668, Fr. Francisco Ignacio Alcina SJ, wrote that some fellow Jesuit missionaries in the Leyte-Samar area, who were very learned in all categories of science, especially in mathematics and astrology, tried to investigate this phenomenon.
All of them became tired of making various computations and measurements and numerous observations, after spending days, months and even years in determining what is regular or irregular about them.
None of them found a definitive answer that would provide a logical pattern for the water movements.
Foolish work
One missionary priest, who was very learned in all kinds of questions, spent many days, lunar phases, months and years noting the data about the limits and boundaries of the water, using certain sticks fixed along the river bank, and some farther and others less so into the waters of the sea, which he had placed for this purpose.
At the end of many months, the investigator showed Alcina how much the water had risen and fluctuated through time.
Even though he did not make a wrong conclusion on the matter, he finally told Alcina that "[he] shall be consumed by a foolish work.”
However, the investigators agreed that a flood tide and an ebb tide occur every day, and were not always simultaneous or had the same force. They said the tide “is greater in the conjunctions and oppositions, that it is like a kind of menstruation (sic).”
Experience
Their experience also showed that sometimes on the day closest to the quarter of the moon, either before or after, the flood tide was customarily greater than on the opposition or conjunction.
On the same days, most of the ebbing did not correspond to the rising tide; sometimes one was greater and at times the other.
All of them seemed to have missed the influence of the full moon as an influence on the high water level.
Alcina said there was no end in the search for a reason for all or even the third part of the tidal phenomenon. These included the moon alone; or the sun accompanied by the moon; or the hollows in the earth in whose depths the tide was believed to extend or retreat; or the fiery conditions that some people dreamed about as in the deep which rarified or condensed it; or even the subterranean fire which they fancied was sufficient for similar ebbing of the tides everywhere.
No one was really sure about the tides when Father Alcina wrote his famous manuscript, “Historias de las islas e indios de Bisayas,” in 1668.
Newton and gravitation
Newton (1642-1727), the English physicist and mathematician, conceived the idea of a universal gravitation in 1666, two years before Alcina wrote his manuscript on this side of the world.
Newton used his idea very successfully to describe the motion of the moon around the earth. But it took him nearly 20 years to publish anything about the bigger problem of the motion of the earth around the sun.
He was prodded to do so by Edmond Halley (1656-1742), a young astronomer who discovered the Halley's Comet and predicted its elliptical 76-year orbit around the sun based on Newton's formula.
Halley financed the publication of Newton's "Principia," a book that was accepted by the Royal Society in 1687 and contained his laws of motion that established the science of mechanics, his discovery of the law of gravitation, and calculus, which has been an essential tool of mathematics and physics ever since.
It has been said that a falling apple might have inspired Newton to conceive his theory of gravitation. But there is little evidence that the apple hit him on the head.