'In regard not only to accuracy of observation, and to detail in publication of the methods of observing, but also to steadiness of system followed through many years, and to completeness of calculation of the useful results deduced from the observations, this work may shame any other collection of observations in this or any other country.'
This catalogue was not Flamsteed's only achievement. He had determined the latitude of the Observatory, the obliquity of the ecliptic, and the position of the equinoctial points. He thought out an original method of obtaining the absolute right ascensions of stars by differential observations of the places of the stars and the sun near to both equinoxes. He had revised and improved Horrox's theory of the lunar motions, which was by far the best existing in Flamsteed's day. He showed the existence of the long inequality of Jupiter and Saturn; that is to say, the periodic influence which they exercise upon each other. He determined the time in which the sun rotates on its axis, and the position of that axis. He observed an apparent movement of the stars in the course of a year, which he ascribed, though erroneously, to the stellar parallax, and which was explained by the third Astronomer Royal, Bradley.
Flamsteed not only met with harsh treatment during his lifetime; he has not yet received, except from a few, anything like the meed of appreciation which is his just due; but, at least, his successors in the office have not forgotten him. They have been proud that their official residence should be known as Flamsteed House, and his name is inscribed over the main entrance of the latest and finest of the Observatory buildings, and his bust looks forth from its front towards the home where he laboured so devotedly for nearly fifty years. But he has received little honour, save at Greenwich, and—in spite of the proverb—in his other home, the village of Burstow, in Surrey, of which he was for many years the rector. Here a stained glass window representing, appropriately, the Adoration of the Magi, has been recently set up to his memory, largely through the interest taken in his history by an amateur astronomer of the neighbourhood, Mr. W. Tebb, F.R.A.S.
No instrument of Flamsteed's remains in the Observatory, his wife removing them after his death. But we may consider his principal instrument, the mural quadrant made for him by Abraham Sharp, as represented by the remains of a quadrant by the same artist, which was presented to the Observatory by the Rev. N. S. Heineken, in 1865, and now hangs over the door of the transit room.
CHAPTER III
HALLEY AND HIS SUCCESSORS
There is no need to give the lives of the succeeding Astronomers Royal so fully as that of Flamsteed. Not that they were inferior men to him; on the contrary, there can be little doubt that we ought to reckon some of them as his superiors, but, in the case of several, their best work was done apart from Greenwich Observatory, and before they came to it.
This was particularly the case with Edmund Halley. Born on October 29, 1656, he was ten years the junior of Flamsteed. Like Flamsteed, he came of a Derbyshire family, though he was born at Haggerston, in the parish of St. Leonard's, Shoreditch. He was educated at St. Paul's School, where he made very rapid progress, and already showed the bent of his mind. He learnt to make dials; he made himself so thoroughly acquainted with the heavens that it is said, 'If a star were displaced in the globe he would presently find it out,' and he observed the changes in the direction of the mariner's compass. In 1673 he went to Queen's College, Oxford, where he observed a sunspot in July and August, 1676, and an occultation of Mars. This was not his first astronomical observation, as, in June, 1675, he had observed an eclipse of the moon from his father's house in Winchester Street.
EDMUND HALLEY.
(From an old print.)
A much wider scheme of work than such merely casual observations now entered his mind, possibly suggested to him by Flamsteed's appointment to the direction of the new Royal Observatory. This was to make a catalogue of the southern stars. Tycho's places for the northern stars were defective enough, but there was no catalogue at all of stars below the horizon of Tycho's observatory. Here, then, was a field entirely unworked, and young Halley was so eager to enter upon it that he would not wait at Oxford to obtain his degree, but was anxious to start at once for the southern hemisphere.
His father, who was wealthy and proud of his gifted son, strongly supported him in his project. The station he selected was St. Helena, an unfortunate choice, as the skies there were almost always more or less clouded, and rain was frequent during his stay. However, he remained there a year and a half, and succeeded in making a catalogue of 341 stars. This catalogue was finally reduced by Sharp, and included in the third volume of Flamsteed's Historia Cœlestis.
In 1678 he was elected Fellow of the Royal Society, and the following year he was chosen to represent that society in a discussion with Hevelius. The question at issue was as to whether more accurate observations of the place of a star could be obtained by the use of sights without optical assistance, or by the use of a telescope. The next year he visited the Paris Observatory, and, later in the same tour, the principal cities of the Continent.
Not long after his return from this tour, Halley was led to that undertaking for which we owe him the greatest debt of gratitude, and which must be regarded as his greatest achievement.
Some fifty years before, the great Kepler had brought out the third of his well-known laws of planetary motion. These laws stated that the planets move round the sun in ellipses, of which the sun occupies one of the foci; that the straight line joining any planet with the sun moves over equal areas of space in equal periods of time; and, lastly, that the squares of the times in which the several planets complete a revolution round the sun are proportional to the cubes of their mean distances from it. These three laws were deduced from actual examination of the movements of the planets. Kepler did not work out any underlying cause of which these three laws were the consequence.
But the desire to find such an underlying cause was keen amongst astronomers, and had given rise to many researches. Amongst those at work on the subject was Halley himself. He had seen, and been able to prove, that if the planets moved in circles round the sun, with the sun in the centre, then the law of the relation between the times of revolution and the distances of the planets would show that the attractive force of the sun varied inversely as the square of the distance. The actual case, however, of motion in an ellipse was too hard for him, and he could not deal with it. Halley therefore went up to Cambridge to consult Newton, and, to his wonder and delight, found that the latter had already completely solved the problem, and had proved that Kepler's three laws of planetary motion were summed up in one, namely, that the sun attracted the planets to it with a force inversely proportional to the square of the distance.
Halley was most enthusiastic over this great discovery, and he at once strongly urged Newton to publish it. Newton's unwillingness to do so was great, but at length Halley overcame his reluctance; and the Royal Society not being able at the time to afford the expense, Halley took the charges upon himself, although his own resources had been recently seriously damaged by the death of his father.
The publication of Newton's Principia, which, but for him, might