Imágenes de página




INTRODUCTION. For the last two hundred years there has been a large class of industrious and intelligent men who have employed themselves in scientific investigations. By them the earth has been explored; they have ascended to the summits of its mountains, and descended into the depths of its cavities. They have measured and weighed the globe itself, and from its strata drawn the materials for the exercise of their ingenuity and skill. With shrewd and patient observation they have combined and separated different substances, searching out their various elements, properties, and affinities. Nothing, in short, has escaped their curiosity and research. The very sunbeam has been stopped by them in its way, and directed through prisms, that they might ascertain its character and composition; which, when discovered, they have applied to copy the forms and colours of the things which the bright beam illuminates. But of all they have done nothing is inore strange, nor more important to the human race, than their investigation of steam, which, by an ingenious mechanical contrivance, they have, in THE STEAM ENGINE, employed as a motive force.

The purposes to which this wonderful triumph of human ingenuity has been applied are numerous and diversified. From depths, inaccessible without its aid, it draws the metal from which other engines may be constructed, and the coal destined to give them activity. By its assistance iron is rolled, drawn, forged, and formed into shapes for machines which it puts into motion, spinning and weaving every article of dress, from the delicate fancy lace to the closely-woven woollen cloth. It lifts, draws, bores, drills, planes, saws, and with an exactitude not to be obtained by any manual skill, may be applied to almost every mechanical process. By its power we are conveyed on land at a speed which, thirty years ago, would have been deemed fabulous ; or transported, with ease and comfort, over river, lake, and sea, in defiance of current, wind, or tide. The question seems no longer to be, steam do ?”. The inquiry rather is, “What remains for it to accomplish?"

This mighty engine is the application of a well-known and easily-understood natural force, but one from which it could scarcely have been imagined that such important results were to be obtained. The vapour which flows in white

" What can

streams from the spout of a tea-kettle when water is boiling, is the moving power of that mechanism by which such varied labours are performed. To describe the gradual steps by which the properties of this vapour and their applicability to the wants of social life were discovered, will form one of the main subjects of this volume.

There is no experiment in the whole range of science which would create more curious wonder than the boiling of water and the production of steam, if it were but novel. T'hat water should be put into a close vessel as a heavy fluid, obedient, like all other solids and liquids, to the law of gravitation, and that after a short period of exposure to heat it should burst out as an elastic, bounding vapour, rising and spreading instead of falling, is a phenomenon quite as surprising as the formation of a solid by the mixture of two liquids, or any other marvel of modern chemistry. But it is generally viewed without interest, because it is daily seen, and what little is known about its properties is commonly learned from household tradition, rather than from thought, or investigation. Few, however, are so ignorant as not to know that when water has been made hot enough to boil, the heat it continues to receive is employed in converting it into steam, and that this steam has a great expansive power. Now it is this property of expansion which gives steam its mechanical force. The same principle which, on a small scale, causes the cover of the tea

kettle to rise, will, when steam is generated in larger vessels, and allowed to gather force by accumulation, lift up the most ponderous weights. To the force of this vapour, indeed, there is no limit but the magnitude and strength of the boilers in which it is generated. If steam, however, come into contact with a cold substance, it is instantly condensed into water, loses its elastic power, and collects in liquid, inert drops upon the substance which has absorbed its heat. How to regulate the ex.pansion and condensation of steam, so as to convert this furious and ungovernable power into a tractable agent, available for the wants of man; how to employ it in lifting weights, or dragging loads, and then to bring it into a liquid inoperative condition, exactly at the instant when it has done what is required, is the problem which, after tasking the energies of successive races of natural philosophers, may be said to have received its solution from the genius of JAMES Watt.

When we examine the ponderous volumes which have been written in explanation of the steam engine, in its numerous varieties of form and construction—all more or less valuable, and worthy of the engineer's attention—we are surprised that one mechanical contrivance should have found employment for so much ingenuity and skill. No other invention, perhaps, has received so many improvements and adaptations. One-hundredth part, indeed, of what has been written upon it would have been

« AnteriorContinuar »