THE

STEAM-ENGINE.

INTRODUCTION.

1. THE STEAM-ENGINE is a machine, in which steam (the vapour of boiling water) is used, and of which the object is, the production of a force, or moving power, by means of which continuous motion may be communicated to other bodies-as the wheels of a carriage; paddles or oars for propelling vessels on water; the rod of a pump for raising water; grindstones for reducing bodies to powder; machinery for spinning, weaving, turning, hammering, boring, communicating pressure, &c.

2. MOTION is the general object of all machines; and, in every sort of machinery, there are two parts which must be carefully distinguished :—First, The machinery which comes into immediate contact with the substance to effect some change upon which is the ultimate object of the operation; second, The engine, or machine, which sets that machinery in motion. The latter is called the first mover, first moving power, or prime mover.

3. In a common turning lathe, or in the case of the

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hand-pump for raising water-in the windmill, or the water-wheel for moving a grindstone-the MAN who, by his muscular power, sets the turning lathe in motion, or works the handle of the pump-the VANES OF THE WINDMILL, and the WATER-WHEEL-are the first movers. It is in them that the motion commencestheir object being simply the production of moving power, which has to be transmitted from them to the machinery which comes into immediate contact with the wood to be turned, the water to be raised, or the corn to be ground. The steam-engine is a FIRST, or

PRIME MOVER.

4. In every case of the production of motion by machinery, the first mover is simply an engine, or machine, so constructed as to take advantage of some natural properties of bodies which are capable of giving rise to motion. In describing the steam-engine, then, there are two things to be considered:-First, Those natural powers resident in bodies by which we can procure a force, or moving power; second, The machine, or engine, by which those powers are made effective for the general production of motion. We shall first direct our attention to the former-the source and mode of action of the natural forces, which, in the steam-engine, give rise to the motion.

5. Infinitely various as these sources of power may, at first sight, appear, and however complex the machinery by which they are applied so as to produce motion, upon analyzing them, it will be found that there are only three sources from which we can obtain a force, or moving power-ANIMAL STRENGTH, ATTRACTION, and REPULSION.

6. Of these, the first and most obvious, and the only one within reach of man in an uncultivated condition, is the MUSCULAR POWER OF ANIMALS, or, as it is frequently called, ANIMAL STRENGTH. This source of

power resides in the muscles-long, fleshy bodies, of a fibrous structure, fixed at each extremity, and possessed of the property of contracting, (diminishing in length,) in obedience to the will of the animal. By this contractile power, the more movable of the points to which the extremities of the muscle are attached, is made to approach the other. These muscles are possessed of great strength, being capable, as has sometimes happened, of breaking the bone to which they are attached. The muscles of the thumb are believed to exert a force nearly equal to a weight of 4000 pounds. We have familiar examples of the application of this power, in the plough, carts and carriages, canal-boats, horse and cattle mills, all set in motion, and continued in that state, by the contractile power of the muscles of animals. This source of power is not made use of in the steam-engine; but the power of an engine is generally estimated by the number of horses that would be required to do the same work-the first steam-engines having been used chiefly as substitutes for horse labour.

7. The other two sources of moving power areFirst, THE ATTRACTION WHICH EXISTS BETWEEN BODIES, and tends to make them approach each other; and, second, THE REPULSIVE POWER, which exists, more or less, in all bodies, and tends to drive their particles asunder. These influences are universally diffused through bodies, and are antagonists-i. e., opposed to each other in their action. They act with great energy, and both have been used as sources of power in the steam-engine. The first is applied in some kinds of engines only (now called atmospheric engines); the latter, either applied directly as a moving power, or used to prepare for the action of the attractive force, has been a leading element in the operation of every sort of steam-engine; and, as steam is the

medium through which the repulsive power is introduced, all are called steam-engines, although the steam may not be the direct cause of the motion. At first, they were termed fire-engines, the steam being formed by the action of fire upon water.

8. The attractive force was taken advantage of by man as a moving power-as in the water-wheel, the windmill, the common pump-long before the repulsive principle was applied, or even thought of, as a source of motion. Now, however, this great power, so long overlooked, has almost entirely superseded the other; acting in the form of steam, it is seen everywhere, and is the prime mover chiefly employed by all civilized nations of modern times.

PART I.

OF THE PHENOMENA OF ATTRACTION AND REPULSION, AND THEIR APPLICATION AS MOVING POWERS.

9. EXCLUDING the vital energy, then, which gives rise to muscular motion and all the phenomena of life, there are two great powers which are (one or other, or both) concerned in producing all the motions and changes which we see going on around us. These are ATTRACTION and REPULSION: they are universally diffused through bodies; and they are antagonists—i. e., opposed to each other in their action.

10. As the latter, Repulsion, is called into action in an unusual degree in bodies which are heated, while its power seems to diminish in proportion as they are cooled, it has generally been regarded as identical with the influence which gives rise to the phenomena of heat.