famous for its beautiful situation, its splendid sands, its noble scenery, its fine old castle and other remains of antiquity, and its mineral waters. 17. DIFFERENT MODES OF ARTIFICIAL LIGHTING. This glorious The great natural source of light is the sun. luminary shines, however, only during the day-time, which in our northern winter lasts for not more than eight hours out of the twenty-four, leaving us for the remaining sixteen hours to the feeble light of the moon and stars, and to any modes of procuring artificial light which we can devise for ourselves. Even in summer the demands of modern civilization require more labour than can be performed during the hours of sunshine; indeed, many of the processes connected with ordinary modern requirements have to be continued without intermission through the whole of the twenty-four hours. "To rise with the lark and to lie down with the lamb" may be a pleasing proverb, and may be well suited to pastoral poetry, but it is utterly useless, and even absurd, as a practical precept. Few, if any, human labours can be carried on efficiently in utter darkness. "The night cometh when no man can work," is a maxim which expresses the same fact in popular and emphatic language. The "blind mole" is so endowed with instinct, and his operations are of such a uniform and simple character, that they can be executed without the assistance of any ray of light, but the wants of civilized man are too varied and complicated to be satisfied by such means. Again, the precious products of human skill and industry require to be protected after they have been called into existence. Darkness is favourable to dishonest undertakings, and therefore,— "When the searching eye of heaven is hid, Behind the globe, that lights the lower world, Without artificial light our lives and property would, to a much larger extent than at present, lie at the mercy of fraud and violence. "Men love darkness rather than light, because their deeds are evil." The skill and knowledge of mankind have, through the whole progress of human history, been employed in discovering and perfecting the means of artificial lighting. From the rude ages of antiquity, when the early inhabitants of the world obtained light by burning the dry materials which first came to hand, down to the present time, when modern science is striving to perfect the application of electricity to the lighting of our streets, public buildings, and ordinary dwellings, the conflict with darkness has continued without intermission. For many generations, candles and oil-lamps were almost the only means available for the lighting of houses. These useful articles are still used; but candles seem to be gradually disappearing, and oil-lamps are being continually improved. Oil was formerly obtained only from the fat of whales and other animals, but is now more conveniently and abundantly found in the form of petroleum or rock-oil. Perhaps the most important discovery hitherto made in connection with artificial lighting is coal-gas. This gas was discovered about the middle of the seventeenth century, but many years elapsed before it was employed for practical purposes. Our streets were formerly lighted by means of oillamps, which cast a dim and uncertain light upon the roads and houses, and great opposition was offered to the general introduction of gas-lamps. They were objected to as dangerous to health, and likely to cause explosions and fires. It was not till 1807 that a portion of London was first lighted with gas. The success of the experiment soon caused its universal adoption, and, in the estimation of the astonished citizens, night was turned into day. In our time this mode of lighting, brilliant as it has hitherto been considered, has met with a formidable rival in the electric light. The advantages of the latter are its far greater illuminating power, the absence of heat, and perhaps the greater economy of the system when it has been fully developed. Electric lighting is probably yet in its infancy. Edison and other famous inventors have exerted their utmost powers in the endeavour to improve it, and render it suitable for employment in our houses and shops. Exhibitions of the systems of various inventors have been held at Paris and at the Crystal Palace. Many thousands of persons have been attracted to the Crystal Palace and to South Kensington by the beautiful effects produced by the electric lamps exhibited to the visitors at these well-known resorts. Parts of London and other European and American cities are now illuminated by the electric light. Various devices have been employed to increase the illuminating power of an artificial light. The most common of these is the reflector, made of polished metal or of glass coated with quicksilver, and so arranged as to throw back or reflect the light which would otherwise pass away into space and be wasted. Reflectors of great power are used in lighthouses, in order that the lights may be intensified to the utmost, and cast their friendly warnings over the sea to the greatest possible distance. In London and other large and crowded cities, reflectors of this kind are used to throw the light of the sun into those parts of a building which are darkened by the proximity of other edifices, which intercept the solar rays. Such reflectors may be regarded as artificial means of obtaining light, though it is obtained from a natural source. 18. OF HEAT; ITS APPLICATIONS AND EFFECTS. The precise nature of heat has not yet been discovered. It does not appear to be an actual substance, for a heated body is no heavier than a cold one. An increase of heat is not accompanied by an increase of weight. It may be produced by simply rubbing two bodies together. All bodies with which we are acquainted possess more or less heat. There is no absolutely cold body—that is, there is none from which heat is altogether absent. Those which are OF HEAT; ITS APPLICATIONS AND EFFECTS. 69 popularly termed cold are only such as contain less than an ordinary amount of heat. Sparks of fire are said to have been obtained out of lumps of ice by striking them sharply together.. The effects of heat are stupendous. By its means the hardest metals can be reduced to a liquid state; coal and other minerals can be converted to a powder, and water can be turned into steam or vapour. The grandest changes in nature are produced by its agency, and the proudest and most durable of the works of man may be utterly destroyed in a short time by its operation. The ordinary action of heat is genial and beneficial. The warm rays of the sun (the great source of heat to our planet) cheer and animate man and the lower animals, and shed a kind and vivifying influence on the vegetable world of trees and flowers. Without heat there would be neither animal nor vegetable life on the surface of our globe. In the extreme polar regions, though they are not quite destitute of heat, there is an entire absence of life; nothing but an unbroken solitude, a pathless desert of snow and ice, surrounds the poles within a radius of two or three hundred miles. Heat is useful to us for other purposes than that of warmth To it we owe our cheerful winter fires, which enable us to defy the frost and snow of Christmas time, and from it we derive the means of cooking our food. Through its powerful agency we are able to carry on the processes of boiling, roasting, and baking, to which we are indebted for our puddings, our cooked vegetables, our roast joints, and even the very bread which is denominated the staff of life. From heat the manufacturer obtains the force which impels his machines, and the enginedriver the power which draws his long train of loaded carriages at the rate of fifty or sixty miles an hour. Without heat to melt iron, copper, gold, and other metals, we should have none of the utensils, ornaments, coins, or other articles made from these substances. Without heat the very blood would be frozen in our veins, and we should soon cease to exist; but for its vital influence we should never even have come into existence. The idea of heat is so intertwined with our ordinary life that it supplies us with many of the figurative expressions employed in our daily conversation. Its metaphorical usage is so common that it almost escapes our observation. We talk of the heat of anger, the warmth of friendship, or the coldness of a reception, without noticing that we are expressing our thoughts in emblematical language. This form of metaphor, like many others most familiar to us, is probably derived from our Authorised Translation of the Bible. Thus we read in Judges ii. 14, that "the anger of the Lord was hot against Israel;" and in 2 Sam. xi. 15, that David commanded Uriah to be placed in the "forefront of the hottest battle." 19. THE POST OFFICE. The Post Office is one of the most useful institutions in this country. Through its agency we can communicate readily, quickly, and cheaply with our absent and distant friends, either by letter or post-card; or, if the business on hand be urgent, by means of the telegraph. If, again, we wish to save small sums of money and at the same time to invest them with perfect safety, and to receive a moderate but certain rate of interest, we can avail ourselves of the Post Office Savings Bank. Its system of immediate and deferred annuities also enables us to make provision for old age by payment of small sums week by week or month by month, as convenient. It gives facilities for purchasing small portions of Government stock more readily and conveniently than through the medium of the Stock Exchange. The Postmaster-General has lately extended still further the advantages of the Post Office, by establishing a Parcel Post, by means of which a parcel, not exceeding seven pounds in weight, can be forwarded to any part of the country for one shilling, while smaller parcels may be sent at lower charges in proportion to weight. |