Flamsteed was succeeded by Halley, particularly famed for his investigations of comets. The next great astronomical event was the discovery of Uranus by Sir William Herschel in 1781. Sir William Herschel also discovered two more of Saturn’s satellites, and began the great work of resolving the Milky Way and other clusters into swarms of suns, single stars into double and triple stars, inquiries into the mysteries of the nebulæ, and in every way enlarging the general conception of the sidereal universe.
To the end of the Eighteenth and beginning of the Nineteenth Centuries belongs the brilliant French astronomer and mathematician Laplace, who published in 1799-1808 his Mécanique Céleste, in which he announced his Nebular Hypothesis (described on page 433 of Vol. II. The discoveries of the Planetoids are described on [pages 396-403], and that of Neptune in 1846 on [pages 430-432]). The latest important additions to the Solar System are the discovery by Prof. Barnard of Jupiter’s Fifth Satellite in 1892 and Saturn’s Ninth by Prof. W. H. Pickering in 1904. The discovery even of a Seventh Satellite of Jupiter has just been announced from the Lick Observatory.
It would be impossible to mention the names of the astronomers whose work from the middle of the last century to its closing years has been distinguished in various fields. Space only permits brief mention of the new methods of research by means of the spectroscope and celestial photography. With the first the name of the English astronomer, William Huggins, is identified and has yielded most important and startling information regarding the composition of heavenly bodies, and with the application of the photographic telescope these new methods have created a revolution in astronomical observation.
It may be interesting to gain a slight idea of the numbers of stars revealed by the camera by referring to Sir Robert Ball:
“If we take a position on the equator, from whence, of course, all the heavens can be completely seen in the lapse of six months, the number of stars that can be reckoned with the unaided eye will, according to Houzeau, amount to about six thousand. If we augment our unaided vision by a telescope of even small dimensions, such as three inches in diameter, the number of stars in the Northern Hemisphere alone is upward of three hundred thousand. We may assume that the Southern Hemisphere has an equally numerous star-population, so that the entire multitude visible with this optical aid is about six hundred thousand. Thus we see that the use of a telescope small enough to be carried in the hands suffices to multiply the lucid stars one-hundredfold. Great telescopes no doubt soon show us that the hundreds of thousands are only the brighter members of a host of millions, and now we receive the assurance of photography that the telescopic stars are only the more conspicuous members of that vast universe. Mr. Roberts indeed declares that the multitudes of stars on the photographic plate grow with each increase of exposure to such a degree that it would almost seem as if the plate would be a wellnigh continuous mass of stars if the operations could be sufficiently protracted.”
Naturally the past years have witnessed the making of new catalogues and maps of stars, and many valuable computations of parallaxes, etc. Some of the results obtained by these new methods are described in the chapters on the Nebulæ and Swarms of Suns, The Great Nebula of Orion, and The Colored, Double, Multiple, Binary, Variable, and Temporary Stars in Vol. I. From this brief survey of the progress of Astronomy the fact will be appreciated, therefore, that all the discoveries and researches have resulted in a larger conception of the universe, and the Solar System sinks into insignificance in the vast ocean of stars and suns.
The study of the Earth’s crust and its contents divested of superstition dates from the end of the Seventeenth Century. Nicolaus Steno (1638-1687), a Dane, devoted himself to geology, and in 1669 observed successive layers of strata. He is called “the father of Palæontology.” In 1680 Leibnitz proposed the theory that the Earth was originally in a molten state. The classification of strata was begun about the middle of the Eighteenth Century. The views of James Hutton (1788), who returned to the theories advanced by Ray (a return to the views of Pythagoras), were continued by Sir Charles Lyell.
Geology and Palæontology have progressed side by side. Among the most famous investigators are Cuvier, Dawson, Marsh, Owen, Huxley, Agassiz, De Blainville, Kaup, Sir Roderick Murchison, Boyd Dawkins, Sir William Flower, R. Lydekker, and E. D. Cope.
To the review of the new developments of meteorology and the science of probabilities by Sir Ralph Abercromby, on pages 784-792 of Vol. II, it is only necessary to add that the interest in meteorological research developed greatly after Torricelli’s discovery in 1643 of weight and pressure in the atmosphere led to the perfection of the barometer and the development of the thermometer and hygrometer, both in the Seventeenth Century. The theory of trade-winds George Hadley announced in the Philosophical Transactions for 1735. Dalton’s Meteorological Essays, published in 1793, and Dr. William Charles Wells’s Theory of Dew, published in 1814, attracted much attention. Regarding the inquiries into the laws of light by Snell, Newton, Descartes, Thomas Young, and Sir George Airy, the reader is referred to the chapter on The Rainbow in Vol. II, by John Tyndall, with whose researches in the latter half of the Nineteenth Century every one is more or less acquainted.
Little need be said here regarding the history of Botany, which is reviewed on pages 984-1000 of Vol. II. We may add, however, that one of the first to revive this study was Otto Brunsfels, whose Historia Plantarum Argentorati was published in two folio volumes with cuts in Strasburg in 1530. He had many followers on the Continent and in England. During the revival of learning, chairs of Botany were founded in the universities; botanic gardens were established in many places (the Jardin des Plantes was founded in 1626); and botanists began to travel to remote countries to search for unknown flora.