Mechanisms
If you are explaining a mechanism, you may follow different orders. You may explain chronologically, showing what happens first, what next, and so on, as in the printing press you would show what happens first to the paper, and then what processes follow. Here you must be careful not to give a long list at the beginning of all the different parts of the machine. Such a list bewilders and is rarely of any real value. Instead of saying, for example, that a reaper and binder consists of a reel, a knife, a canvas platform and belt, etc., you will do well to simplify at the beginning, and say, perhaps, that from the front the machine looks like a dash with an inverted V at one end: thus: ____Λ and then go on to relate the various parts to this simple scheme. The brief paragraph which follows illustrates the principle in a slight space.
The stone-boat is a peculiar vehicle incidental to America, and has nothing whatsoever to do with the water. It resembles a huge metal tray or shovel hauled by a team of horses. And its special path is as novel as the boat itself. It is only two wooden lines fashioned from tree-logs adzed roughly flat on the upper side, well greased, and laid promiscuously and roughly parallel on the ground. The stone is prized and levered on to the tray, and hauled with a speed, which, bearing in mind the primitive road, is astonishing, to the dump, where a sharp swing round on the part of the horses pitches the mass down the bank.[58]
If you prefer, you can use, instead of the chronological order, the device of showing what the need was for the machine and how it fills the need, or what the object of the machine is and how it accomplishes that object. An explanation of the cotton gin might present the woeful waste of time before the gin was invented and then show how the invention annuls that waste. One of the periscope might state the object of invisible observation and then show how, by tubes and mirrors, this object is accomplished. Or finally, as a third general method, you may state the root principle and then expand in detail. With this scheme you might state that the piano is an instrument in which felt hammers strike metal strings that are stretched across a sounding board, and then go on to show the significance, as related to this notion, of keys, pedals, music rest, and other details. Often this method is the most helpful for a reader, since it gives him at once a nucleus of theory round which he can group the details with immediate or rapid understanding of their relations and significance. In so simple a machine as the ice cream freezer to introduce names like "dasher" without previous warning may result in momentary confusion, whereas if the principle is stated at the beginning, and the reader knows that the object is to bring the cream into contact with the coldest possible surface so as to produce speed in freezing, the "dasher," when mentioned, is at once significant. The description and explanation of a track-layer, which follows, is so made as to be both clear and interesting.
The track-layer is one of the most interesting tools with which the railway-builder carries out his epoch-making work. It is a cumbersome, ungainly, and fearsome-looking implement, but with a convincing, grim, and business-like appearance. From the front it resembles a gallows, and for this reason has earned the sinister sobriquet of "the gibbet" among certain members of the engineering fraternity. On the front of the truck there is a lofty rectangular scaffolding of rigid construction, strongly based and supported for the hard, heavy work it has to perform. A jib runs forward into the air from the bottom of either leg to meet at the outer extremity and to form a derrick. The car on which the structure is mounted carries a number of small steam-engines, each of which has to perform a particular function, while at the commanding point high up on the rectangular construction is a small bridge, from which the man in control of the machine carries out his various tasks and controls the whole machine. Ropes, hooks, and pulleys are found on every side, and though, from the cursory point of view, it appears an intricate piece of mechanism, yet its operation is absurdly simple.
This machine constitutes the front vehicle of the train, with the bridge facing the grade and the projecting boom overhanging the track. Immediately behind are several trucks piled high with steel rails, fish-plates to secure connection between successive lengths of rails, spikes, and other necessaries. Then comes the locomotive, followed by a long train of trucks laden with sleepers. On the right-hand side of the train, level with the deck of the trucks, extends a continuous trough, with its floor consisting of rollers. It reaches from the rearmost car in the train to 40 or 50 feet in advance of the track-layer, the overhanging section being supported by ropes and tackle controlled from the track-layer truck whereby the trough can be raised and lowered as desired.
The appliance is operated as follows. The engine pushes the fore-part of the train slowly forward until the end of the last rail laid is approached. The rollers in the trough, which is in reality a mechanical conveyor, are set in motion. Then the gangs of men stationed on the rear trucks with might and main pitch the bulky sleepers into the trough. Caught up by the rollers, the ties are whirled along to the front of the train, and tumble to the ground in a steady, continuous stream. As they emerge, they are picked up by another gang of men who roughly throw them into position on to the grade. Other members of the gang, equipped with axes and crowbars, push, pull, haul, and prize the ties into their relative positions and at equal distances apart.
When thirty or forty sleepers have been deposited in this manner, a pair of steel rails are picked up by the booms from the trucks behind the track-layer, are swung through the air, and lowered. As they near the ground ready hands grasp the bar of steel, steady it in its descent, and guide it into its correct position. The gauge is brought into play dexterously, and before one can realize what has happened the men are spiking the pair of rails to the sleepers, have slipped the bolts into the fish-plates connecting the new rail with its fellow already in position, and the track-layer has moved slowly forward some 13 or 16 feet over a new unit of track, meanwhile disgorging further sleepers from the mouth of the trough.
The noise is deafening, owing to the clattering of the weighty baulks of timber racing over the noisy rollers in the conveyor, the rattle of metal, and the clang-clang of the hammers as the men with powerful strokes drive home the spikes fastening the rail to its wooden bed, and the hissing and screeching of steam. Amid the silence of the wilderness the din created by the track-layer at work is heard for some time before you can gain a glimpse of the machine train. The men speak but little, for the simple reason that they could scarcely make themselves heard if they attempted conversation. Each moves with wonderful precision, like a part of an intricate machine.
In this way the rail creeps forward relentlessly at a steady, monotonous pace. The lines of sleepers and rails on the track disappear with amazing rapidity, and the men engaged in the task of charging the conveyor-trough and swinging the rails forward, appear to be in a mad race with steam-driven machinery. The perspiration rolls off their faces in great beads, and they breathe heavily as they grasp and toss the weighty strips of timber about as if they were straws. There is no pause or diminution in their speed. If they ease up at all the fact becomes evident at the front in the course of a few seconds in a unanimous outcry from the gangs on the grade for more material, which spurs the lagging men on the trucks behind to greater effort. The only respite from the exhausting labor is when the trucks have been emptied of all rails or sleepers and the engine has to run back for a further supply, or when the hooter rings out the time for meals or the cessation of labor.
The track-layer at work is the most fascinating piece of machinery in the building of a large railway. The steam-shovel may be alluring, and the sight of a large hill of rock being blown sky-high may compel attention, but it is the mechanical means which have been evolved to carry out the last phase—the laying of the metals—that is the most bewitching. One can see the railway growing in the fullest sense of the word—can see the thin, sinuous ribbon of steel crawling over the flat prairie, across spidery bridges, through ravine-like rock-cuts, gloomy tunnels, and along lofty embankments. Now and again, when the apparatus has secured a full complement of hands, and every other factor is conducive, the men will set to work in more deadly earnest than usual, bent on setting up a record. Races against time have become quite a craze among the crews operating the track-layer on the various railways throughout America, and consequently the men allow no opportunity to set up a new record, when all conditions are favorable, to slip by.[59]