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CONSTABLE

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CONSTANTINE I

the force found necessary to produce upon a gram of matter a velocity of one centimeter a second. The form of energy to which all other energies can be reduced is that of heat. The proof, therefore, of the conservation of energy in any system depends upon the measurement of heat in terms of motion. That heat could so be measured was advanced as a theory by Count Rumford and Sir Humphrey Davy in 1798, and by Julius Robert Mayer in 1842; but it was first publicly demonstrated by James Frescott Joule in 1843. In 1845 he was able to state that the energy required to heat one gram of water at i° C. is the same as that required to lift about 423 grams to a height of one meter. This result is very near that which is at present accepted.

According to the theory of matter which regards it as composed of very small particles moving and attracting one another, all potential energy is a kind of strain. There are strains of extension, of compression and of distortion, of electrification, of magnetization, of chemical separation and of gravitation. Perhaps all these may really be called strains of distortion. Kinetic energy may be of the following kinds, all of which are regarded as forms of motion: translation, rotation, vibration; and, as subclasses of these, heat, current-electricity, light, chemical activity, emanation (as in radio-activity) and probably other forms of motion. Now it seems that all these forms of energy, potential and kinetic, are transformable into heat; but heat is transformable into other kinds of energy only when there exists a difference of temperature between different parts of a system. Wherever, in any system, differences of temperature are in whole or in part removed, therefore, the energy of heat which that system contained is in whole or in part changed from being available into a condition of being unavailable for transformation into any other kind of energy. Now in any and all systems, in whatever processes they undergo, there takes place this transformation of available into useless energy. The useless energy is called the entropy of the system.

The theory of the conservation of energy is not understood until it is supplemented by this theory of the destruction or dissipation of available energy in all systems and throughout the universe. The grandest application of this theory open to us is undoubtedly the recognition of the sun and the earth, together with the surrounding ether, as a conservative system. Then the transformation of the heat of the sun into light, into the uplift of waters from the oceans, into the chemical energy of plants and of animals, into the resultant deposits of sediment and the erosion of mountain-ranges, into the heat of coal and the energy

of Niagara, with all the applications of these forces to meet human necessities; the spectacle of all these countless changes and productions is dominated by the thought that of the energy thus poured forth none is lost, but abides in a potential or a kinetic form. And yet the available energy is continually diminished, as these changes, one and all, end their career in the form of heat, thereby continually diminishing the difference of temperature between the sun and that which surrounds it. Nevertheless we must remember that, admirable and consistent as these theories of conservation and entropy appear, they are subject to revision with the advance of knowledge and of mechanical art. PERCY HUGHES.

Constable, John, an English landscape-painter, was born in 1776 and died in 1837. He entered the Royal Academy when 23 years old, but his progress was slow. Not until 1814, 12 years after he had begun to exhibit pictures, did he succeed in selling one. But in 1819 his View on the Stour attracted much attention, and his reputation spread widely. His pictures are remarkable for the truth and vividness with which they reproduce country-scenes and the phases of nature. A French critic said that their leaves and grass are fresh with dew, and Fuseli jokingly asserted that they made him call for his umbrella. Among his best paintings are Salisbury Cathedral, The Cornfield, The Lock and The Valley Farm

Con'stance, Lake, lies 1,290 feet above the sea, between Switzerland and Germany, north of the Swiss Alps. It is forty-two miles long and seven and a half miles in average width, covering an area of 208 square miles; its greatest depth is 906 feet. The Rhine flows through it from east to west. The shores are formed by hilly lands; cornfields, vineyards, orchards and wooded hills, with here and there a ruined castle, surround the lake. The water is dark green, and in the spring often rises ten or twelve feet after a thaw. The fisheries are important.

Constantino I (kon'stan-ttn'}, Roman emperor, called the Great, born 274 A. D., was the son of Constantius Chlorus. When 22 years old, he served as a soldier in Egypt and in Persia. In 305 Constantius and Galerius became emperors respectively of the west and the east. Constantine was now in the army of Galerius, who saw a possible rival in the young leader's brilliant genius and popularity among the soldiers, and so took every means to place him in danger. But Constantine hastily joined his father in the west, and on his death succeeded him in 306. However, things got into a muddled condition two years later, for six emperors were ruling at once, three in the east and three in the west. Constantine thus found himself opposed by two