II U Y H U Y the progress of science. At that time geology in any proper senss of the term did not exist. Mineralogy, however, had made considerable progress. Hutton s taste for cliemistry niturally led him into mineralogy. But he had conceived larger ideas than were entertained by the mineralogists of his day. He desired to trace back the origin of the various miner vis and rocks, ani thus to arrive at some clear under standing of the history of the earth. For many years he continued to ponder over the subject, making during that time many excursions to different parts of the country to obtain materials for his researches, or to test the hypotheses he had been led to form. At last, in the spring of the year 1785, he communicated his views to the recently established Royal Society of Edinburgh in a paper entitled Theory of the Earth, or an Investigation of the Laws Observable in the Composition, Dissolution, and Restoration of Land upon the Globe. In this remarkable work the doctrine is ex pounded that geology is not cosmogony, but must confine itself to the study of the materials of the earth ; that everywhere evidence may be seen that the present rocks of the earth s surface have been formed out of the waste of older rocks ; that these materials having been laid down under the sea were there consolidated under great pressure, and were subsequently disrupted and upheaved by the expansive power of subterranean heat ; that during these convulsions veins and misses of molten rock were injected into the rents of the dislocated strata; that every portion of the upraised land, as soon as exposed to the atmosphere, is subject to decay ; and that this decay must tend to advance until ths whole of the land has been worn away and laid down on the s^a-floor, whence future upheavals will once more raise the consolidated sediments into new land. In some of those broad and boll generalizations Hutton was anticipated by ths Italian geologists; but to him belongs the credit of having first perceived their mutual relations, an 1 combined them in a luminous coherent theory every where based upon observation. It was not merely the ground beneath us to which Hutton directed his attention. He had long studied the changes of the atmosphere. The same volume in which his Theory of the Earth appeared contained also a Theory of Rain, which was read to the Royal Society of Edinburgh in February 1784. He contended that the amount of mois- t ire which the air can retain in solution increases with augmentation of temperature, and therefore that on the mixture of two masses of air of different temperatures a portion of ths moisture must be condensed and appear in visible form. He investigated the data available in his time regarding rainfall and climate in different regions of ths globe, and came to the conclusion that the rainfall is everywhere regulated by the humidity of the air on the one hand, and the causes which promote mixtures of different aeri il currents in the higher atmosphere on the other. The vigour and versatility of his genius may be under stood from the variety of works which, during his thirty years residence in Edinburgh, he gave to the world In the year 1792 he published a quarto volume entitled Dissertations on different Subjects in Natural Philosophy, ia which he discussed the nature of matter, fluidity, co hesion, light, heat, and electricity. Some of these subjects were further illustrated by him in papers rerl before the Royal Society of Edinburgh. He did not restrain himself within the domain of physics, but boldly marched into that of metaphysics, publishing three quarto volumes with the title An Investigation of the Principles of Knowledge, and of the Progress of Reason -from Sense to Science and Philo sophy. In this work he develops the idea that the external world, as conceived by us, is the creation of our own minds influenced by impressions from without, that there is no resemblance between our picture of the outer world and the reality, yet that the impressions produced upon onr minds, being constant and consistent, become as much realities ta us as if they precisely resembled things actually existing, and therefore that our moral conduct must remain the same as if our ideas perfectly corresponded to the causes producing them. His closing years were devoted to the extension and republication of his Theory of the Earth, of which two volumes octavo appeared in 1795. A third volume, necessary to complete the work, was left by him in manuscript, and is referred to by his biographer Playfair, but seems to have disappeared. No sooner had this task been performed than he set to work to collect and systematize his numerous writings on husbandry, which he proposed to publish under the title of Elements of Agriculture. He had nearly completed this labour when an incurable disease brought his active career to a close on 26th March 1797. It is by his Theory of the Earth that Hutton will be remembered with reverence while geology continues to be cultivated. The author s style, however, being somewhat heavy and obscure, the book did not attract during his lifetime so much attention as it deserved. Happily for science Hntton numbered among his friends John Playfair, professor of mathematics in the university of Edinburgh, whose enthusiasm for the spread of Hutton s doctrine was combined with a rare gift of graceful and luminous exposition. Five years after Hutton s death lie published a volume, Illustrations of the HuUonian Theory of the Earth, in which he gave an admirable sum mary of that theory, with numerous additional illustrations and arguments. This work is justly regarded as one of the classical con tributions to geological literature. To its influem-e much of the sound progress of British geology must be ascribed. In the year 1805 a biographical account of Hutton, written by Playfair, was published in vol. v. of the Transactions of the Royal Society of Edinburgh. (A. GE.) HUY, in Flemish HOEY, a town of Belgium, at the head of an arrondissement in the province of Liege, situated in the most romantic portion of the Meuse valley near the confluence of the Hoyoux, on the railway between Liege and Namur, and about 20 miles west of the former city. It lies on both banks of the river, and the two portions are united by a bridge about 460 feet long. Of best note among the buildings are the town-house, the court-house, the hospital, and the collegiate church of Notre Dame, which is an excellent specimen of Gothic architecture, dating originally from the 14th century, but restored in the course I of the 16th and the 19th. The citadel of Huy is now demolished. It was a powerful fortress, constructed between 1817 and 1822 on the site of the older castle dismantled by the Dutch in 1718. Part of the works were excavated in the solid rock, and the whole building looked down on the valley of the Meuse with picturesque defiance. Of the industrial activity of the town the most important results are paper, tin-plate, zinc, iron, earthenware, and brandy ; and iron, zinc, and coal are extensively wrought in the vicinity. Ths population in 1876 was 11,774. Huy, in modern Latin Hoium, Hogum, Huyum, and Huum, ! existed at least as early as the 7th century, and according to some I authorities it was founded in 148 by the emperor Antoninus. Coins of Charles the Simple are extant with the legend in Vico . Hoio. The older name of the district in which it is situated was the Condroz, or territory of the Condrosii. Under the prince- bishops of Liege Huy was a- prosperous place, and it possessed no fewer than fifteen churches, as well as a number of monasteries, fora population of about 5000. It was in one of its suburbs that the ablmy of Neufmoustier was founded by Peter the Hermit, who died and was buried within its precincts (1115). Part of the cloisters are still standing ; and a monument was erected iu 1858 by M. Godin, the owner of the grounds, to mark the site of the hermit s tomb. Huy was captured by the Dutch in 1595, and in 1693 it was taken and burned by the French. The Dutch were in possession from 1702 till 1718, when they restored the town to the emperor. See Gorissen s edition of Melard, Hist, de la villc d du chateau dc Huy, Huy, 1839. HUYGENS, CHRISTIAAN (1629-1695), mathematician, mechanician, astronomer, and physicist, was born at the Hague, April 14, 1629. He was the second son of Constan-
tin Huygens, noticed below. From his father Christiaan
