Triumphs of Invention and Discovery in Art and Science. Fyfe James Hamilton

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СКАЧАТЬ dimensions, molten metal is poured into the corners of the pan for the purpose of maintaining the fluid pressure on the mould, and thus securing a good and solid cast. For if the pan were allowed to cool more slowly, the thin metallic film at the back of the inverted plaster mould would probably solidify first, and thus prevent the fluid pressure which is necessary for filling up all the lines of the mould.

      Tomlinson concludes his description of these interesting processes by informing us that an experienced and skilled workman will make five dips, each containing two octavo pages, in the course of an hour, or, as already stated, at the rate of nearly ten octavo sheets a day.

      When the pan is opened, the cake of metal and plaster is removed, and beaten upon its edges with a mallet, to clear away all superfluous metal. The stereotype plate is then taken by the picker, who planes its edges square, "turns" its back flat upon a lathe until the proper thickness is obtained, and removes any minute imperfections arising from specks of dirt and air-bubbles left among the letters in casting the mould. Damaged letters are cut out, and separate types soldered in as substitutes. After all this anxious care to obtain perfection, the plate is pronounced ready for working, and when made up with the other plates into the proper form, it may be worked either at the hand-press or by machine.

      Other modes of stereotyping have been introduced, but not one has attained to the popularity of the method we have just described.

      The Steam Engine

      "It is said that ideas produce revolutions and truly they do – not spiritual ideas only, but even mechanical." – Carlyle.

      I. – THE MARQUIS OF WORCESTER

      As the last century was drawing to its close, two great revolutions were in progress, both of which were destined to exercise a mighty influence upon the years to come, – the one calm, silent, peaceful, the other full of sound and fury, bathed in blood, and crowned with thorns, – the one the fruit of long years of patient thought and work, the other the outcome of long years of oppression, suffering, and sin, – the one was Watt's invention of the steam engine, the other the great popular revolt in France. These are the two great events which set their mark upon our century, gave form and colour to its character, and direction to its aims and aspirations. In the pages of conventional history, of course, the French revolution, with its wild phantasmagoria of retribution, its massacres and martyrdoms, will no doubt have assigned to it the foremost rank as the great feature of the era, —

      "For ever since historians writ,

      And ever since a bard could sing,

      Doth each exalt with all his wit

      The noble art of murdering."

      But those who can look below the mere surface of events, and whose fancy is not captivated by the melo-drama of rebellion, and the pageantry of war, will find that Watt's steam machine worked the greatest revolution of modern times, and exercised the deepest, as well as widest and most permanent influence over the whole civilized world.

      Like all great discoveries, that of the motive power of steam, and the important uses to which it might be applied, was the work, not of any one mind, but of several minds, each borrowing something from its predecessor, until at last the first vague and uncertain Idea was developed into a practical Reality. Known dimly to the ancients, and probably employed by the priests in their juggleries and pretended miracles, it was not till within the last three centuries that any systematic attempt was made to turn it to useful account.

      But before we turn our attention to the persons who made, and, after many failures and discouragements, successfully made this attempt, it will be advisable we should say something as to the principle on which their invention is founded.

      The reader knows that gases and vapours, when imprisoned within a narrow space, do struggle as resolutely to escape as did Sterne's starling from his cage. Their force of pressure is enormous, and if confined in a closed vessel, they would speedily rend it into fragments. Let some water boil in a pipkin whose lid fits very tightly; in a few minutes the vapour or steam arising from the boiling water, overcoming the resistance of the lid, raises it, and rushes forth into the atmosphere.

      Take a small quantity of water, and pour it into the hollow of a ball of metal. Then with the aid of a cork, worked by a metallic screw, close the opening of the ball hermetically, and place the ball in the heart of a glowing fire. The steam formed by the boiling water in the inside of the metallic bomb, finding no channel of escape, will burst through the bonds that sought to confine it, and hurl afar the fragments with a loud and dangerous explosion.

      These well-known facts we adduce simply as a proof of the immense mechanical power possessed by steam when enclosed within a limited area. Now, the questions must have occurred to many, though they were themselves unable to answer them, – Why should all this force be wasted? Can it not be directed to the service and uses of man? In the course of time, however, human intelligence did discover a sufficient reply, and did contrive to utilize this astonishing power by means of the machine now so famous as the Steam Engine.

      Let us take a boiler full of water, and bring it up to boiling point by means of a furnace. Attach to this boiler a tube, which guides the steam of the boiler into a hollow metallic cylinder, traversed by a piston rising and sinking in its interior. It is evident that the steam rushing through the tube into the lower part of the cylinder, and underneath the piston, will force the piston, by its pressure, to rise to the top of the cylinder. Now let us check for a moment the influx of the steam below the piston, and turning the stopcock, allow the steam which fills that space to escape outside; and, at the same time, by opening a second tube, let in a supply of steam above the piston: the pressure of the steam, now exercised in a downward direction, will force the piston to the bottom of its course, because there will exist beneath it no resistance capable of opposing the pressure of the steam. If we constantly keep up this alternating motion, the piston now rising and now falling, we are in a position to profit by the force of steam. For if the lever, attached to the rod of the piston at its lower end, is fixed by its upper to a crank of the rotating axle of a workshop or factory, is it not clear that the continuous action of the steam will give this axle a continuous rotatory movement? And this movement may be transmitted, by means of bands and pulleys, to a number of different machines or engines all kept at work by the power of a solitary engine.

      This, then, is the principle on which the inventions of Papin, the Marquis of Worcester, Newcomen, and James Watt have been based.

      The great astronomer Huyghens conceived the idea of creating a motive machine by exploding a charge of gunpowder under a cylinder traversed by a piston: the air contained in this cylinder, dilated by the heat resulting from the combustion of the powder, escaped into the outer air through a valve, whereupon a partial void existed beneath the piston, or, rather, the air considerably rarified; and from this moment the pressure of the atmospheric air falling on the upper part of the piston, and being but imperfectly counterpoised by the rarified air beneath the piston, precipitated this piston to the bottom of the cylinder. Consequently, said Huyghens, if to the said piston were attached a chain or cord coiling around a pulley, one might raise up the weights placed at the extremity of the cord, and so produce a genuine mechanical effect.

      But Experiment, the touchstone of Physical Truth, soon revealed the deficiencies of an apparatus such as Huyghens had suggested. The air beneath the piston was not sufficiently rarified; the void produced was too imperfect. Evidently gunpowder was not the right agent. What was? Denis Papin answered, Steam. And the first Steam Engine ever invented was invented by this ingenious Frenchman.

      Papin was born at Blois on the 22nd of August 1645. He died about 1714, but neither the exact date nor the place of his death is known. The lives of most men of genius are heavy with shadows, but Papin's career was more than ordinarily characterized by the incessant pursuit of the evil spirits of adversity СКАЧАТЬ