The Story of Astronomy (13 page)

In spite of the severe weather the Royal Society still managed to hold its regular meetings, albeit poorly attended by reason of the extreme cold. The problem of gravitation was a topic very much under discussion, and the astronomers were convinced that the Sun somehow exerted an attractive force on the planets. In Holland Christiaan Huygens (1629–95) had recently published a formula for what he called the centrifugal force—this was the outward thrust experienced by a body such as a planet moving uniformly around a circle. (It was the same outward force that is experienced by a child riding on a roundabout.) This formula for centrifugal force, the astronomers knew, was one of the key factors required to solve the problem of the planetary orbits.

After one of the meetings of the Royal Society three of the members, namely Edmond Halley (1656–1742), Christopher Wren (1632–1723) and Robert Hooke (1635–1703) retired to a coffee house to discuss between themselves the problem of gravitation and how it related to what they called
“the system of the world.”
At this time Wren was
turned 50 and Hooke was in his late 40s. They knew each other from their days at Oxford after the Civil War. Halley was the junior member; he was only 26. All three of them had come to the conclusion that the law of gravity was an inverse square law. All three knew that this hypothesis could not be raised to the status of a law unless Kepler's laws of planetary motion, which by now were accepted as established fact, could be proved from it.

But the required proof was a very intricate and taxing mathematical problem. Christopher Wren had tried to solve the problem and he had to admit failure. Edmond Halley was a very able mathematician but he also admitted that his attempt had failed. Perhaps it was a problem that could never be solved. Robert Hooke was not a man to admit failure, however; he coyly announced that he had solved the problem but that he would keep his solution to himself so that others trying to solve it would know the value of his work. Christopher Wren did not believe his friend Hooke had a solution, however, and he offered a book to the value of 40 shillings to anybody who could solve the problem.

A few weeks later it became clear to both Wren and Halley that Hooke's demonstration was not forthcoming. If the problem were to be solved then there was but one person in the whole of England with the mathematical skills to do it, and they all knew that he lived at Trinity
College in Cambridge. Somebody must travel to Cambridge and confront Isaac Newton with the problem.

Robert Hooke was definitely the wrong man to make the visit. Newton had taken offense when Hooke had exposed an error in his work to the Royal Society, and Hooke's credibility with Newton was at rock bottom. Christopher Wren was the obvious man to go to Cambridge. First, Newton thought very highly of Wren's skill as a mathematician. Second, while at Cambridge, Wren could witness the progress on the library at Trinity College which he had designed. But Wren was too busy rebuilding London after the Great Fire to spare any time uncovering the secrets of the universe. It was the younger man, Edmond Halley, who had to visit Cambridge and gain an audience with the Lucasian Professor of Mathematics.

Edmond Halley had not met Newton before, but he knew of his awesome reputation. He also knew of Newton's desire for privacy and that he did not suffer fools gladly. Halley was in no hurry to go to Cambridge, and by the time he made the journey in August 1684 the hard winter was history. In the English countryside it was harvest time, and the corn was being reaped with sickle and scythe by every available farmhand in the rural villages. When Halley arrived at Cambridge he had no problem in finding the
Lucasian Professor of Mathematics. He was greeted by a figure with a sharp nose, a prematurely gray but full head of hair and slightly protruding and deeply penetrating eyes. It was Isaac Newton himself. Halley had little notion about how Newton would respond to his request, and he must have been pleased when Newton turned out to be friendly and cooperative. After a little small talk and a few formalities Halley came to the point of his visit by asking the all-important question regarding the system of the world. What did Isaac Newton think would be the orbit of a planet around the Sun, supposing the attraction of the Sun to be
“reciprocal to the square of its distance from it”?
Newton replied immediately that it would be an ellipse. Halley asked him how he knew the answer.
“Why,”
said Newton,
“I have calculated it.”

Edmond Halley was amazed. He asked Newton for his calculation. The absentminded professor obligingly began to rummage through his papers as Halley watched with trepidation. Newton was unable to find his paper, but Halley did not doubt for a moment that the man before him was telling the truth. Isaac Newton had already solved the key problem at the heart of the theory of gravitation! Torn between joy and dismay Halley watched in awe as he realized that the man before him carried one of the great secrets of the universe in his head! But try as he might Newton was unable to find the paper with
the written solution. It was small wonder that Halley's next act was to ask Newton to rework his calculation.

It says much for Halley's tact and diplomacy that he returned from Cambridge with a promise from Newton to renew the necessary calculation and to supply Halley with a copy. It leaves a few questions unanswered, however. Was Newton's study a disorganized chaos of papers and half-completed experiments, or was it as neatly organized as his mind? Perhaps Newton knew exactly where his calculation was but wanted time to think about it before showing it to Halley. Why was Newton, who was always complaining about the demands on his time, so cooperative with Edmond Halley? Newton was well aware of Halley's astronomical work in the southern hemisphere, and at their meeting the two must have discussed many topics in which they had a common interest. Halley told Newton about his findings in St. Helena, where his pendulum clock ran more slowly at the top of a mountain. Newton had read the account already in the
Philosophical Transactions
, but there was no substitute for talking to the author face-to-face. Newton probably expounded his ideas on the comet of 1680–81, and he set Halley thinking about the motion of comets and the possibility that they could return after a number of years. The
outcome was that when Halley left Cambridge he became progressively more convinced that Newton's ideas must be written up and published for the world to see and read. He knew that the Royal Society was by far the best body to handle the publication.

Halley was very fortunate. He arrived at Cambridge at a time when Newton's researches on alchemy were getting nowhere and his academic life was progressing toward a dead end. The latest discoveries on gravitation had given Newton some new ideas to work on, and he realized that his golden opportunity had arrived and that the time was right to make his researches known to the world. He decided it was his duty to write up and publish these ideas for posterity. He knew they would generate controversy in the world of natural philosophy, but for once he was prepared to publish them and face the consequences.

It took Isaac Newton about a year to put his great work together, which he called
Philosophiae Naturali Principia Mathematica
(
The Mathematical Principles of Natural Philosophy
), usually simply known as
Principia
. Much of it was a synopsis of the problems he had solved over the previous 20 years. He started by formulating his three laws of motion, which today form the basis of mechanics and dynamics. Newton's three laws of motion describe the way bodies move when acted on by a force. The first
law states that a body remains at rest or in uniform motion in a straight line unless acted on by a force. We know that moving bodies on Earth slow down and stop, but this is because they are acted on by the forces of friction and wind pressure. If these forces were removed the bodies would continue to move in a straight line forever unless an external force acted upon them.

The second law states that a force changes the motion of a body in the direction of the force. The acceleration of the body depends on its mass and the value of the force. A good example is a train moving in a straight line with a constant force. In such conditions it generates uniform acceleration. For a planet moving around the Sun and drawn to it by gravity, the law is complex but still holds true.

The third law states that for every action there is an equal and opposite reaction. If you sit on a chair, your weight becomes a downward force on the chair. The chair exerts an equal upward force, known as the reaction, on you. When two billiard balls strike each other the result is more complex, but Newton's law shows that the balls experience equal and opposite reactions. These laws appear to apply only to earthbound objects, but Newton went on to show how the same laws could be applied to the motion of the planets around the Sun. He showed how the whole system of the Sun and the planets could
be explained from a single law—the law of universal gravitation. Newton used his method of fluxions to arrive at his results, but he reworked them into a classical form so that mathematicians could understand them more readily. The result was a work explaining the whole system of the world in detail, but encompassed in classical mathematics. Future generations would use calculus to solve the problems, leaving Newton's classical proofs in an isolated time warp of their own.

It was 1687 when Newton's great work
Principia
was published and his astronomical works became known to the world. He is remembered as a great scientist and philosopher as well as an astronomer. He retained an interest in astronomy until his death in 1727, and during his lifetime he saw many advances in both the practical and theoretical sides of astronomy.

Finally, we must thank Humphrey Newton (fl. 1629–95), a distant relative and assistant to Isaac Newton, for leaving us with this simple but fascinating picture of a master scientist and his often distracted thoughts:

When he has sometimes taken a turn or two [about the garden], has made a sudden stand up, turn'd himself about, [he would] run up the stairs like another
Archimedes, with an “eureka” fall to write on his desk standing without giving himself the leisure to draw a chair to sit down on. At some seldom times when he designed to dine in the hall, would turn to the left hand and go out into the street, when making a stop when he found his mistake, would hastily turn back, and then sometimes instead of going into the hall, would return to his chamber again.

The Royal Society—the national academy of science—was founded in England in 1660 with the purpose of discovering the truth about scientific matters through experiment. In about 1663 some scientists began to hold regular private meetings in Paris, and in 1666 French government minister Jean-Baptiste Colbert (1619–83) was instrumental in formally establishing the group. It gained royal approval, becoming known as the Académie Royale des Sciences. The mission of the Académie Royale des Sciences was to study ways in which the sciences could be exploited to the advantage of the kingdom.

Jean-Baptiste Colbert was also founder member of the Académie des Inscriptions et Belles-Lettres, an establishment set up earlier to choose inscriptions for medals and monuments celebrating the military victories of the Sun King, Louis XIV (1638–1715). (A third foundation, the
Académie Royale d'Architecture, was set up in 1671. Its purpose was to lay down the rules and refine the taste of formal French architecture.) Two French scientists who prepared the ground for the Académie Royale des Sciences, but who died before it was founded, were Marin Mersenne (1588–1648) and René Descartes (1596–1650). In 1611 Mersenne joined the Roman Catholic mendicant Order of Minims in Paris, and from 1614 to 1619 he taught philosophy at the Minim convent at Nevers. He was an ardent opponent of the pseudoscientific doctrines such as alchemy, astrology and related arcane arts, and this was mainly why he vigorously supported true science. He defended the philosophies of René Descartes and the astronomical theories of Galileo (1564–1642). He taught philosophy at the convent L'Annonciade in Paris, and from 1620 onwards he traveled throughout western Europe. Pierre Gassendi (1592–1655) was another French astronomer who did not live to see the foundation of the Académie Royale des Sciences. In about 1614 Gassendi received a doctorate in theology at Avignon and was ordained in the following year. He was persuaded by Mersenne to abandon mathematical and theological pursuits, but he took up astronomy and in 1631 he was the first to observe a transit of the planet Mercury across the face of the Sun.

One of Mersenne's most important contributions to science was his long service as a communicator between philosophers and scientists throughout Europe. In his time there were no published scientific journals to distribute knowledge, and sometimes scientists such as astronomers could work for a lifetime on the same project without even knowing the existence of other workers in the field. Mersenne met many scientists on a regular basis and he corresponded at length with Descartes, Girard Desargues (1591–1661), Pierre de Fermat (1601–65), Blaise Pascal (1623–62) and Galileo. Mersenne was such a good communicator it was said that to inform him of a discovery meant to publish it throughout the whole of Europe.

From the 1660s onwards there was always great rivalry between the astronomical and other scientific establishments of England and France. It made for a competitive spirit, and it was responsible for many creative advances in both countries. In most cases the knowledge was published and willingly shared with similar scientific establishments in other developed countries such as Italy, Denmark, Holland and Germany. It was common for members of the French academy to travel to London to meet the Royal Society, and it was equally common for English scientists to make the return trip to Paris. The French had one advantage over the English, however,
because for most of Europe Paris was more accessible than London, and so scientists from countries such as Italy, Germany and the Netherlands were more common at their meetings.