4. THE SACRAMENT OF FIRE JOHN OXENHAM Kneel always when you light a fire! And on the ascending flame inspire Of warmth and light; For here again is sacrifice For your delight. Within the wood, That lived a joyous life Through surny days and rainy days And winter storms and strife; Within the pea That drank the sweet, The moorland sweet, Of bracken, whin, and sweet bell-heather, While snug below in sun and snow, Where forests lie entombed, Oak, elm, and chestnut, beech, and red pine bole; God shrined His sunshine and enwombed For you these stores of light and heat, Your life-joys to complete. These all have died that you might live; 269448A To loose their long captivities, Kneel always when you light a fire! And grateful be For God's unfailing charity! 5. HOW MEN MADE HEAT WORK FRANKLIN T. JONES Read this selection so that you will be able to give a clear, connected account of its contents. To do this, carefully read the selection and then glance over it as a whole to discover the main parts of the author's thought and the order in which these parts come. ANIMALS AS SOURCES OF POWER At first man learned to add to his own strength that of the animals. The Eskimo trained his dog to help him draw a sled over the ice. In the ancient world and even down to modern times the ox has been a helper on the farm and on the journey. The natives of India use the elephant to help them carry their burdens and to lift logs for them in their lumbering. The horse has long been used by man; in the early days only for what were considered the more important and nobler services, such as carrying man himself, and in warfare. POWER FROM WIND AND WATER After the use of animals came the harnessing of the wind and water. In the earliest days we find that man knew how to use the wind to drive his boats. The war boats of the Greeks and Romans, unable to rely on the uncertain wind, were driven by oars, but the merchant boats, which did not have to move so regularly, were carried along with the help of sails. Still later the wind was harnessed by the invention of the windmill and was used to grind grain, thus helping man in what had been up to that time one of the most laborious of his tasks. After a time man also learned to use the power of the swift streams to do his work. Water is even now one of the most important sources of power. The building of great electric plants in mountain regions where water power is abundant promises to be increasingly a source of profit to man and an aid to industry. With every new kind of power which he has taken into his service man has found new reasons for making tools and machinery. Without the help of a plow the ox could not till the soil, for the plow is a kind of hand supplied to the animal by the wisdom of man. It would be hard to decide which required the greater intelligence on the part of man, to make the plow or to tame the ox. In the same way the use of wind to drive a boat means making a sail and setting up a mast in the boat. The power of the river can be used only by the man who can invent a water wheel. Machinery needs power to drive it, and power is of no use until it is harnessed by machinery. HEAT AS A SOURCE OF POWER There is one kind of power in the world which it took man a long time to learn to use. That power is heat. The comfort that comes from a fire and the usefulness of a fire in cooking food were known in the earliest ages, but the use of heat to lift weights and to save human strength was possible only after man had gone a long way on the road of invention. The first successful method of using heat for power was devised in the tin mines of England in the seventeenth century. These mines could be worked only when they were kept free from water. We are told that pumping out the water from one of these mines required the labor of five hundred horses and the men to drive them. SAVERY'S ENGINE In 1698 Thomas Savery secured a patent for a pumping device which was the first steam engine. It looked not at all like a modern engine. It had no wheels or moving shafts, but it used heat to do work. The work that it did was to suck water out of the mines, making heat from a coal fire do what men and horses had done before. Savery's engine was by no means economical of fuel. It is easy to understand what we mean by the statement that a machine wastes power. If a man who is trying to lift something can not get hold of it in such a way as to apply all of his strength, his lifting will be very wasteful. We try to make it easy to lift things by putting handles on them. Handles are inventions intended to save human energy. In exactly the same way when a machine can not use its power as it should, there is waste. Savery's engine was wasteful because the tank had to be first heated and then cooled, and a great deal of power thus went to waste. It has been calculated that Savery's engine used steam so that he obtained only about one-twentieth of the work that can be secured from the same amount of steam in a modern engine. Even a modern engine does not use all the power that there is in steam. Anyone who has seen the steam escaping from a locomotive will realize that a good deal of heat is wasted even in the most perfect modern engine. NEWCOMEN'S ENGINE The problem of saving heat and using it to the best advantage has been one of the reasons for constant improvement in machinery. Within a few years after Savery had invented his engine a new pumping engine was invented by Thomas Newcomen. This mechanism worked very much better than Savery's pump and came into extensive use in pumping water out of mines. Many pumping engines of the Newcomen type were manufactured, making possible the enlargement of the mines. In some cases the mines were sunk to twice the depth that was formerly possible, thus opening up rich stores of new ore. WATT'S ENGINE Accident plays a great part in the history of men and even of nations. James Watt (1736-1819) was not permitted by the guilds or trades-unions to open an instrument-maker's shop in Glasgow. As a result he secured employment at the University of Glasgow to repair apparatus. A model of a Newcomen engine was brought into the shop for repair. Watt at once saw that to work properly a steam engine should always work while hot instead of while alternately hot and cold, as engines previously invented had operated. He realized that steam, and hence fuel, could be saved and an engine be made capable of doing more work by keeping the cylinder and working parts heated. He therefore introduced a condenser, which accomplished the result desired. The original piston steam engine of Newcomen and Watt resembled the modern gas engine in the fact that its cylinder was closed at one end only. The force due to the steam was all applied inside the closed end. In economizing steam Watt closed both ends of the cylinder and then applied steam alternately on both sides of the piston. Since that time engines have been doubleacting; that is, steam is admitted first at one end, then at the other end of the cylinder. Watt also made use of the expansive power of steam, though it remained to later inventors to perfect the high-pressure, non-condensing steam engines which we are accustomed to use. Since Watt's day, invention after invention has improved and perfected the steam engine until we have the powerful engines of modern times. THE POWER OF ENGINES What the engine does for us can be made clear by one or two comparisons. Thomas Savery used the word "horsepower" in telling about the work of his pump. James Watt took over the word "horsepower" and gave it a more exact meaning. He estimated that the average cart-horse of London could travel at the rate of 21⁄2 miles an hour and at the same time raise, by means of a rope led over a pulley, a weight of 150 pounds. This is equivalent to raising a weight of 33,000 pounds one foot high in one minute. When we say, then, that a locomotive has 1,500 horsepower we mean that this locomotive has 1,500 times the power necessary to raise 33,000 pounds one foot, or the power of raising 49,500,000 pounds one foot, in one minute. The same truth can be put in another way by comparing the carrying power of a freight train with the carrying power of men. A freight train can carry more wheat from Kansas City to Chicago in a given time than could be transported on the backs of 1,000,000 men. |