Galileo Galilci (b. 1564, d. 1642) first applied the telescope (which he made from a general description of the instrument of Hans Lipperhey of Holland, who was the first inventor of the telescope) to the investigation of the heavens. Ile was rewarded by the discovery of on the moon's surface. The important discoveries of the four satellites of Jupiter, the ring of Saturn—not then distinctly recognized as a circle— the spots on the sun, and the crescent form of Venus, followed in quick succession.
For propagating the Copernican doctrine of the world, Galileo incurred the displeasure of the priests, and was compelled by the Inquisition to retract his opinions.
But the eternal laws of nature are not to be suspended by the recantation of a philosopher forced by the tyranny of priestcraft. The earth moved grandly on round the sun in spite of both; and scientific truth was now too old to remain in the restrictive leading-strings of any ecclesiasticism.
The next great epoch in the history of A. brings us to England and Newton (b. 1642, d. 1727). In the interval, practical A. had profited largely by the logarithms of Napier; the mathmatical researches of Descartes; the application of the telescope to the quadrant by Gaseoigne, an Englishman, and afterwards by Auzout and Picard; by Homer's dis covery of the progressive motion, and measurement of the velocity, of light; by the invention of Vernier; and the application of the pendulum to clocks by Huygliens, who also brought into use the spiral spring, and made some valuable observations on the ring and satellites of Saturn; as well as by the investigations of Norwood, Horrocks, Hooke, Hevelius, Gilbert, Leibnitz, and Domiuicus Cassini, to the last of whom especially the scientific world owes much. Among a variety of other valuable observations and dis coveries may be mentioned his thorough investigation of time zodiacal light, his deter mination of the rotations of Jupiter and Mars, and of the motions of Jupiter's satellites from their eclipses, his discovery of the dual character of Saturn's ring, and also of four of his satellites. Newton's fame rests upon his discovery of the law of gravitation, upon which the common belief is lie was led to speculate by the fall of an apple. Newton announced his discovery in the Principle in 1687, which was briefly that every particle of matter is attracted by, or gravitates to, every other particle of matter, with a force inversely proportional to the squares of their distances. The first gleam of this grand conclusion is said to have so overpowered Newton that he had to suspend his calculations, and call in a friend to finish the few arithmetical computations that. Were incomplete. This discovery is perhaps the grandest effort of human genius of which we have any record. Newton also made the important discovery of the revolution of comets round the sun in conic sections, proved the earth's form to be an oblate spheroid, gave a theory of the moon and tides, invented fluxions, and wrote upon Optics.
While the foundations of physical A. were thus broadly laid by Newton, Flamsteed —the first astronomer-royal at Greenwich, to whom, until recently, .scantjustice has been done—and Halley were greatly improving and extending the practical department of the science. To the former we are indebted for numerous observations on the fixed stars, on planets, satellites, and comets, and for a catalogue of 2884 stars. His Historia aeleslis formed a new era in sidereal A. Dr. Halley, who succeeded Flamsteed as astronomer-royal, discovered the accelerated mean motion of the moon, and certain inequalities in Jupiter and Saturn, but he is most famed for his successful investigations into the motions and nature of comets. His successor was Dr. Bradley, who, in the year of Newton's death, made the important discovery of the aberration of light, which furnishes the only direct and conclusive proof we have of the earth's annual motion. To him also we are indebted for our knowledge of the notation of the earth's axis. Ile was, besides, an unwearied observer, and left behind him at his death upwards of 60,000 observations. Altogether, Bradley's is deservedly one of the most honored names in modern A. Dr. Maskelyne, who was appointed to the observatory after Bradley, origi nated the Nautical Almanac.
Merely to mention the names of men who from the death of Bradley to the present time have added, by theory and practice, to our knowledge of A., would extend, this synopsis much beyond the limit necessarily assigned to it.. If the 18th c. opened with lustre derived from the physical demonstrations of Newton, it closed magnificently with the telescopic discoveries of Sir William Herschel, who added to our universe a primary planet (Uranus) with its satellites, gave two more satellites to Saturn, resolved the milky way into countless myriads of stars, and unraveled,the mystery of nebulm and of double and triple stars. Laland, Lagrange, Lacaille, and Delambre, in the latter bait of the 18th c., did much by their researches and analyses to systematize and improve the science of A. The instrumental means of observation were also, during that time brought to high perfection. Laplace, in his great work the llecanique Celeste (1799 1808), gave what further proof was needed of the truth and sufficiency of the Newtonian theory, The 19th c. opened with the discovery of the four small planets—Ceres, in 1801, by Piazza; Pallas and Vesta by Olbers—the former iu 1802, and the latter in 1807; and Juno, by Harding, in 1804. In 1845, Hencke discovered the fifth of this group revolving between Stars and Jupiter, to which the name of Asti.= was given; and by the end of 1879, 200 planetoids (q.v.) had been discovered. The greatest event of the century has been the discovery of the planet Neptune in 1846.