and other works from the pen of the late R. A. Proctor, which, although slightly out of date in details, give lucid and interesting descriptions of the celestial wonders; while for those who wish to recognise the heavens it is essential to make use of Peck's 'Constellations and How to Find them,' Maunder's 'Astronomy Without a Telescope,' Gore's Star Groups,' and Proctor's 'Half-Hours with the Stars.'

The advanced student will probably know what to read on his special branch of the science, but the following books may be recommended: Ball's 'The Earth's Beginning,' W. H. Pickering's 'The Moon,' Elger's 'The Moon,' Young's 'The Sun,' Lowell's 'Mars,' Proctor's 'Saturn,' Ball's 'Story of the Sun,' Lowell's 'The Solar System,' Gore's 'The Worlds of Space' and 'The Stellar Heavens,' and Serviss's 'Pleasures of the Telescope.' Astrophysics, the new astronomy, is more technical than the older branch of the science, but is lucidly expounded in Miss Clerke's 'Problems in Astrophysics' and Scheiner's Astronomical Spectroscopy,' while the problem of the construction of the heavens

is described in the works of the three great masters of the subject: Proctor's 'Universe of Stars,' Gore's Visible Universe,' and Newcomb's 'The Stars.' Astronomy, like every other science, tends every year to become more specialised and intricate, and the reader is apt to become confused in the multiplicity of details. In order to have a clear view of the science, he should read Miss Clerke's History of Astronomy during the Nineteenth Century.' Another good way of studying astronomy is to read it biographically. Tycho Brahe,' by Dreyer, and 'Galileo,' by Fahie, are indispensable to all interested in astronomy; while the life and work of Herschel is admirably described by Sime in his volume on 'Herschel' in the World's Epoch-Makers Series, and by Miss Clerke in her work, 'The Herschels and Modern Astronomy.' There is also an interesting biography of Kepler in Brewster's 'Martyrs of Science.' Strange to say, no adequate life of Newton has yet appeared, the only one being Brewster's 'Life,' which cannot be placed beside the magnificent works on Tycho Brahe, Galileo, and Herschel. Shorter biog

raphies are to be found in Ball's Great Astronomers' and Morton's Heroes of Science.'

If the student is anxious to pursue the subject further, and to read the lives of the nineteenth-century astronomers, he cannot do better than peruse Dunkin's Obituary Notices of Astronomers,' and the admirable obituary notices published yearly by the Royal Astronomical Society. Other books worth consulting are Lockyer's 'Primer of Astronomy,' Schiaparelli's 'Le Stelle Cadenti,' which Lockyer calls the greatest contribution to astronomical literature which the last century produced. Schiaparelli's latest work, 'L'Astronomia nell' Antico Testamento,' has an especial bearing on the astronomy of the Bible. In this volume the great Italian astronomer throws much light on the astronomical knowledge of the Hebrews, which appears to have been considerable. Schiaparelli shows that some passages in the Bible, especially in Job, Amos, and Ezekiel, indicate that the Hebrews were acquainted with the planets Venus and Saturn, with eclipses, meteoric showers, and other astronomical phenomena.

CHAPTER VIII.

SCIENCE: CELESTIAL EVOLUTION.

THE human mind is not content with mere observation of celestial phenomena. From time immemorial astronomers have attempted to look before and after, to read the past history and speculate on the future of the marvellous panorama of the heavens. To Kant is commonly assigned the credit of originating the nebular hypothesis in its present form. It should be stated, however, that a remarkable speculation as to the origin of the solar system was made by our own James Ferguson, who conceived the idea that the matter now forming the sun and planets originally existed in detached

condition throughout space, and that the various particles were drawn together by the force of gravitation to form the celestial

bodies.

From this it will be seen that Ferguson anticipated the main feature of the theories of Kant and Laplace.

In his 'Natural History of the Heavens,' published in 1755, Kant traced the formation of the solar system from the contraction of a vast mass of evenly diffused particles of matter. This theory was unknown to Laplace, who in 1796 propounded his theory of the evolution of the solar system at the close of his popular work, 'The System of the World.' The great French astronomer noticed that in the solar system all the planets revolved round the sun in the same direction, from west to east, and that the satellites of the planets obeyed the same law. He also observed that the sun, moon, and planets rotated on their axes in the same direction as they revolved round the sun. It was plain that this was not the result of chance. But Laplace also noticed that the planets revolved round the sun, and the satellites round their primaries in almost the same plane as the earth moved, the "plane of the ecliptic." This added further evidence to the impossibility that the movements of