Our rude ancestors long ago discovered its great utility, and they cudgeled their brains to aid the flame of fire and obtain a still fiercer heat. The bellows was the result--the wind pointed the way to this invention. Then followed by slow degrees the acquirement of further knowledge concerning fire and its uses. Our forefathers learned the processes of melting and smelting--later were established various metallurgical operations. The path was thus prepared for Tubal Cain and other artificers in metals. Man eventually became exceedingly skilled in applying heat forces in his many requirements in articles of brass, tin, zinc, steel, etc. HEAT--EXPANSION AND CONTRACTION. From an article by J. Gordon Ogden, Ph.D., in “Popular Mechanics,” September, 1910, we quote: “Expansion is one of the most remarkable of the phenomena to be reckoned with in the natural world. Practically every bit of matter from the Great Brooklyn Bridge to the tiny hairspring in one’s watch is under its imperial domination. It is a tremendous force, and the world of mechanics has to treat it with the deference and respect due to its gigantic power. Unlike gravity, and other forces of nature, it is whimsical and takes sudden fits and starts, now acting one way, now another. It affects different bodies in different ways, and seems to be at variance with the time-honored forces whose action can be predicted under all circumstances. At least that is what it apparently does. In our meagre knowledge of the great underlying laws that control the universe it is possibly unwise to speak so unkindly of expansion, as though it were a spoiled child in need of correction; its behavior, however, is so contrary to what one might expect that one is at a loss to say anything else. “The walls of a building are sometimes rectified by the enormous force exerted by the contraction of iron rods. Bars of iron are placed so as to join the two walls where the bulging is most pronounced. These bars terminate in screws furnished with nuts. The whole of their length is heated and the nuts tightened. On cooling the bars will contract with practically irresistible force, causing the walls to straighten up. This operation is repeated until the rectification is completed. Boiler plates are fastened with red-hot rivets. The contraction of the rivets incident upon their cooling draws the plates tightly together, forming a steam-proof joint.”