From heat comes all power. When the latent forces of Nature were first set aflame by primitive man he touched the spring of civilization. Since that time fire has been working for human progress. It is one of the most powerful agents in the development of civilization.
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.”
“Tyndall, in his work on heat, gives an excellent illustration of the force of expansion and contraction. ‘The choir of Bristol Cathedral was covered with sheet lead, the length of the covering being 60 feet and its depth 19 feet 5 inches. It had been laid in the year 1851, and two years afterward it had moved bodily down for a distance of 18 inches. The descent had been continually going on from the time the lead had been laid down, and an attempt to stop it by driving nails into the rafters had failed, for the force with which the lead had descended was sufficient to draw out the nails. The roof was not a steep one, and the lead could have rested on it forever without sliding down by gravity. What, then, was the cause of the descent? The lead was exposed to the varying temperatures of day and night. During the day the heat imparted to it caused it to expand. Had it lain upon a horizontal surface, it would have expanded all around; but as it lay upon an inclined surface it expanded more freely downward than upward. When, on the contrary, the lead contracted at night its upper edge was drawn more easily downward than its lower edge upward. Its motion was, therefore, exactly like that of a common earthworm; it pushed its lower edge forward during the day and drew its upper edge after it during the night, and thus by degrees it crawled through a space of 18 inches in two years.’
“Mention has been made in a preceding article of the effect of unequal expansion upon two different metals that have been bolted together. It is by this principle that the action of the ordinary thermostat, so familiar now as a controller and regulator of the temperature of high buildings, is explained—a rod made up of two different metals whose rates of expansion are different. When the temperature of the room in which the thermostat is placed becomes too high the rod curls toward the metal point S and touches it, completing an electrical contact which causes a motor to shut off the draft. When the temperature of the room falls below a certain point the rod curls in the opposite direction toward the metal point T. This causes a motor to open the draft and thus furnish a more abundant supply of hot air.