While we watch the steamer glide around Castle Garden into East River, evening begins to come on; we must hasten uptown. As we pass along Broadway, lights flash out in the darkness and our thoughts are again turned to fire and steam. We have heard that the source of the electric light is in the dynamo, and that steam power is used to turn that great machine. The enormous engine, the mammoth boat, the brilliant light--all need the power of steam, and nothing but fire will produce this steam. What, then, is fire? and is its only use that of changing quiet, liquid water into powerful steam? Let us see. Did you notice that machine shop which we passed when we were in Cleveland a few days ago? Did you see those furnaces with the huge volumes of flame bursting out of the open doors? You know that great heat is necessary to make tools and other implements of iron, and all the instruments of everyday life that are formed out of metals. Our pens and needles, our hoes and rakes, our horseshoes, our stoves and furnaces, our registers and the iron of our desks--all depend upon heat for their production. Fire can do much for us. To change water into steam is but one of its powers. Fire and heat are behind most of the operations of modern life. As we open the door of the house we are met by a current of warm air rushing out into the chilly evening. It is the last of October, and in the middle of the day windows and doors have been left wide open to let in all the light and warmth of the bright sunshine. But it is evening now, and the sun has long since sunk below the horizon; it no longer gives us any of its heat. All night the air will grow colder and colder, and were we unprotected by clothing we should suffer from the chill atmosphere. Even coverings are not sufficient to keep the heat of our bodies from passing off into the air, just as the warm air rushed out through the open hall door. It has been found necessary to warm the air in our houses so that the bodily heat, which we need to sustain life, may not so easily be lost. The heat which the sun furnishes us is called natural heat; that which is produced by the skill of man is called artificial heat. This artificial heat is used for a fourth purpose also. As we have seen, it makes steam for the locomotive, the steamboat, and other engines; it is necessary in the manufacture of tools and various utensils out of iron and other metals; and it warms our houses and schools, our offices and stores. It is also used everywhere and by everybody in cooking. Had we no fires or artificial heat of some sort we should have to eat our meat and fish raw; we could only mix our meal and flour with cold water, which would not be palatable to most of us; our vegetables, uncooked, would fail to satisfy us; and many of us would find ourselves limited to fruits and nuts, which would be hardly sufficient to keep us in good health, to say the least.