III. ASTRONOMY

The stars were subjected to science in a hundred countries. In Italy the Jesuit astronomer Riccioli (1650) discovered the first double star—i.e., a star which to the eye seems one but is seen through the telescope as two stars apparently revolving around each other. In Danzig Johannes Hevelius built an observatory in his own home, made his own instruments, catalogued 1,564 stars, discovered four comets, observed the transit of Mercury, noted the moon’s librations (periodic alternations in the visibility of its parts), charted its surface, and gave to several of its features names that remain on lunar maps today. When he announced to Europe’s stargazers that he could distinguish stellar positions as accurately with a diopter (a sight using only one lens or prism) as with a compound telescope, Robert Hooke challenged the claim; Halley traveled from London to Danzig to test it, and reported that Hevelius had told the truth. 21

Recognizing the importance of astronomy for navigation, Louis XIV provided funds to raise and equip an observatory at Paris (1667–72). From that center Jean Picard led or sent expeditions to study the skies from different points on the earth; he went to Uraniborg to note the exact location from which Tycho Brahe had made his classic map of the stars; and, by a variety of observations ranging from Paris to Amiens, he measured a degree of longitude with such accuracy (within a few yards of the current figure, 69.5 miles) that Newton is supposed to have used Picard’s results to estimate the mass of the earth and verify the theory of gravitation. By similar observations Picard reckoned the equatorial diameter of the earth at 7,801 miles—not far from our present computation of 7,913 miles. 22 These findings made it possible for a ship at sea to determine its location with unprecedented precision. So the commercial expansion and industrial development of Europe urged on the scientific revolution, and profited from it.

At Picard’s suggestion Louis XIV invited to France the Italian astronomer Giovanni Domenico Cassini, who had already acquired European fame by discovering the spheroidal form of Jupiter and the periodic rotation of Jupiter and Mars. Arrived in Paris (1669), he was received by the King as a prince of science. 23 In 1672 he and Picard sent Jean Richer to Cayenne, in South America, to observe Mars at its maximum “opposition” to the sun and nearness to the earth; Cassini noted the same opposition from Paris. The comparison of the simultaneous observations from these two separate points gave new and more precise values to the parallax of Mars and the sun and their distance from the earth, and revealed vaster dimensions in the solar system than had been estimated before. As a pendulum was found to beat more slowly at Cayenne than a similar pendulum at Paris, the astronomers concluded that gravity was less intense near the equator than in higher latitudes; and this suggested that the earth was not a perfect sphere. Cassini thought it was flattened at the equator; Newton thought it was flattened at the poles; further research supported Newton. Meanwhile Cassini discovered four new satellites of Saturn, and the division (now known by his name) of Saturn’s ring into two. After Cassini’s death in 1712 he was succeeded in the Paris observatory by his son Jacques, who measured the arc of the meridian from Dunkirk to Perpignan, and published the first tables of the satellites of Saturn.

Christian Huygens, before joining the cosmopolitan assemblage of scientists in Paris, made at The Hague some important contributions to astronomy. With his brother Constantijn he developed a new method of grinding and polishing lenses; with these he constructed telescopes of greater power and clarity than any known before; thereby he discovered (1655) the sixth satellite of Saturn, and that planet’s mysterious ring. A year later he made the first delineation of the bright region (now bearing his name) in the Orion nebula, and detected the multiple character of its nuclear star.

The great rival to the Paris astronomers was the remarkable group that gathered mostly around Halley and Newton in England. James Gregory of Edinburgh lent distant aid by designing the first reflecting telescope (1663)—i.e., one in which the rays of light from the object are concentrated by a curved mirror instead of a lens; Newton improved this in 1668. In 1675 John Flamsteed and others addressed to Charles II a memorial asking him to finance the building of a national observatory, so that better methods of calculating longitude might guide the English shipping that was now plowing the seas. The King provided for the building, which was raised in the borough of Greenwich near southeast London; this came to be used as the point of zero longitude and standard time. Charles offered Flamsteed a small salary as director, but nothing to pay for assistants or instruments. Flamsteed, frail and sickly, gave his life to that observatory. He took pupils, bought instruments out of his personal funds, received others as gifts from friends, and set himself patiently to chart the sky as seen from Greenwich. Before he died (1719) he had made the most extensive and accurate star catalogue yet known, considerably improving on that which Tycho Brahe had left to Kepler in 1601. Harassed by lack of aid, doing himself the paperwork usually left to assistants, Flamsteed angered Halley and Newton by delays in the calculation and announcement of his results; at last Halley published them without Flamsteed’s permission, and the ailing astronomer shook the stars with his wrath.

Nevertheless Edmund Halley was the finest gentleman of them all. An enthusiastic schoolboy student of the sky, he published at twenty a paper on the planetary orbits; and in that same year (1676) he set out to see how the heavens looked from the southern hemisphere of the earth. On the island of St. Helena he charted the behavior of 341 stars. On the eve of his twenty-first birthday he made the first full observation of a transit of Mercury. Back in England, he was elected a fellow of the Royal Society at twenty-two. He recognized Newton’s genius, financed the first edition of the costly Principia, and prefixed to it some complimentary verse in splendid Latin, ending in the line, Nec fas est proprius mortali attingere divos (It is not allowed to any mortal to come closer to the gods). 24 Halley edited the Greek text of the Conies of Apollonius of Perga, and learned Arabic to translate Greek treatises preserved only in that language.

He wrote his name in the sky by one of the most successful predictions in history. Borelli had paved the way by discovering the parabolic form of cometary paths (1665). When a comet appeared in 1682 Halley found similarities in its course with comets recorded in 1456, 1531, and 1607; he noted that these manifestations had come at intervals of some seventy-five years, and he predicted a reappearance in 1758. He could not live to see the fulfillment of his prophecy, but when the comet returned it received his name, and added to the rising prestige of science. Until late in the seventeenth century comets were considered to be direct acts of God, portending great calamities to mankind; the essays of Bayle and Fontenelle, and the prediction of Halley, laid this superstition. Halley identified another comet, seen in 1680, with one observed in the year of Christ’s death; he traced its recurrence every 575 years, and from this periodicity he computed its orbit and speed around the sun. Commenting on these calculations, Newton concluded that “the bodies of comets are solid, compact, fixed, and durable, like the bodies of the planets,” and are not “vapors or exhalations of the earth, of the sun, and other planets.” 25*

In 1691 Halley was refused the Savilian chair of astronomy at Oxford on suspicion of being a materialist. 26 In 1698, on a commission from William III, he sailed far into the South Atlantic, studied the variations of the compass, and charted stars as seen from the Antarctic. (Compared with this expedition, said Voltaire, “the voyage of the Argonauts was but the crossing of a bark from one side of a river to the other.” 27) In 1718 Halley pointed out that several of the supposedly “fixed stars” had altered their positions since Greek times, and that one of them, Sirius, had changed since Brahe; allowing for errors of observation, he concluded that the stars vary their positions relative to one another over great periods of time; and these “proper motions” are now accepted as real. In 1721 he was appointed to succeed Flamsteed as astronomer royal; but Flamsteed had died so poor that his creditors seized his instruments, and Halley found his own work hampered by inadequate equipment as well as by his own declining energies; nevertheless he began, at sixty-four, to observe and record the phenomena of the moon through its complete cycle of eighteen years. He died in 1742, aged eighty-six, after wisely drinking a glass of wine against his doctor’s orders. Life, like wine, should not be taken in excess.

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