Expository Writing

by Mervin James Curl

This root principle, nucleus, core, kernel can often be stated in one sentence. You can say, for instance, in speaking of bridges like those across the East River, "A suspension bridge consists of a roadway hung by wires from huge cables which are anchored at the ends and are looped up over one or more high supports in the stream." This sentence may not be immediately and entirely clear, but it serves to show quickly what relations parts have to each other, and to it the reader may refer in his mind when detailed treatment of the maze of wires and bolts becomes bewildering. Often this sentence need not be expressed alone; it should always be thought out in the writer's mind.

If it is expressed, such a sentence may stand at the beginning as a sort of quick picture, or it may come at the end as a collecting statement of what has preceded, or at any point where it seems to be of the most value to the reader. It may take various forms as, for example, it may state in essence how the machine or process works, is operated, or what it is for, or of what it consists. If it occurs at the end as a summary, it may be a summary of facts in which the points made or the parts described are enumerated, or it may be a summary of essence, in which the significance or the principle of the thing is stated. In the following examples the sentence will be found near the beginning in both cases, and in the nature of a statement of the principle of operation.

Of tools used for cutting, perhaps the most remarkable of all is the oxygen blow-pipe. This is a little tool something the shape of a pistol—which a workman can easily hold in one hand. It is connected by a flexible tube to a cylinder of compressed oxygen, and by another tube to a supply of coal-gas. Thus a jet of oxygen and a jet of coal-gas issue from the nozzle at the end of the blow-pipe, and, mingling there, produce a fine point of flame burning with intense heat. If this be directed upon the edge of a thick bar or plate of steel it will in a few seconds melt a tiny groove in it, and, if the pipe be moved along, that groove can be developed into a cut and in that way very thick pieces of steel can be severed quite easily. The harder the steel, too, the more easily it is cut, for hard steel contains more carbon than soft, and that has a tendency to burn with oxygen, actually increasing the heat of the flame. A bar of iron a foot long can be cut right down the center in fifty seconds. It is said that scientific burglars have been known to use blow-pipes to open safes with; but a very strange thing about them is that, while they will cut hard steel of almost any thickness almost like butter, they are completely baffled by a thin sheet of copper. The reason of this is that copper is such a good conductor of heat that the heat of the flame is conducted quickly away, and so the part in contact with the flame never becomes hot enough to melt.[55]

There is another very efficient substitute for the dynamite cartridge, which may abolish blasting even in hard-rock mines. It is a hydraulic cartridge, or an apparatus that works on the principle of the hydraulic jack. Unlike dynamite, which consists of a lot of stored and highly concentrated energy that is let fly to do what destruction it may, the hydraulic cartridge is absolutely inert and devoid of potential energy when placed in the blast-hole. Only after it is in place is the energy applied to it. This it gradually accumulates until it acquires enough to burst open the rock without wasting a lot of energy in pulverizing it. The apparatus is under the direct control of the miner all the time. There is nothing haphazard about its operation.

The cartridge consists of a strong steel cylinder, made in various sizes. Disposed at right angles to the length of the cylinder are a number of pistons, or rams, that may be forced out laterally by pumping water into the cylinder. The cartridge is introduced into the blast-hole with the rams retracted. Then a quick-action pump is operated to move the rams out so that they come in contact with the rock. After this, by means of a screw-lever a powerful pressure is exerted upon the water, which forces out the rams until the rock gives way under the strain.[56]

Processes

The development of this kind of exposition will vary somewhat according to the nature of the subject. If you are explaining a process—how to make a campfire, or how to find the width of an unbridged river, or how to make bread—you will naturally follow the chronological order and tell what to do first, what second, and so on. If several materials are to be used in the process, you may enumerate them all at the beginning, for collection, or state them piece by piece as they are needed. For example, you may say, "In making a kite you will need so many pieces of such wood of such and such sizes, with paper or cloth, strong twine, glue, nails, etc." You may cast the whole process into a personal mood by telling how some one, perhaps yourself, did it on a previous occasion. This method, if it is judiciously used, adds interest. You must take care not to seem to encumber obviously simple directions, however, with the machinery of personal narrative so that the whole account is longer than it should be. In case you are treating some process in which mistakes are easily made, you can often help the reader by showing how some one—preferably yourself—did it wrongly and thereby came to grief. Or you can state concisely what not to do if there is chance for mistake. In developing films, for example, you may warn the reader not to mix any of the Hypo with the Fixing Bath; in picking his apples not to break the twigs of the tree; in paddling a canoe through rapids not to become excited. Note how, in the account which follows of how to handle a punt, the author makes the material quite human and personal—to the reader's pleasure.

You may get yourself a tub or a working-boat or a wherry, a rob-roy or a dinghy, for every craft that floats is known on the Thames; but the favorite craft are the Canadian canoe and the punt. The canoe you will be familiar with, but your ideas of a punt are probably derived from a farm-built craft you have poled about American duck-marshes—which bears about the same relationship to this slender, half-decked cedar beauty that a canal-boat bears to a racing-shell.

During your first perilous lessons in punting, you will probably be in apprehension of ducking your mentor, who is lounging among the cushions in the bow. But you cannot upset the punt any more than you can discompose the Englishman; the punt simply upsets you without seeming to be aware of it. And when you crawl dripping up the bank, consoled only by the fact that the Humane Society man was not on hand with his boat-hook to pull you out by the seat of the trousers, your mentor will gravely explain how you made your mistake. Instead of bracing your feet firmly on the bottom and pushing with the pole, you were leaning on the pole and pushing with your feet. When the pole stuck in the clay bottom, of course it pulled you out of the boat.

Steering is a matter of long practice. When you want to throw the bow to the left, you have only to pry the stern over to the right as you are pulling the pole out of the water. To throw the bow to the right, ground the pole a foot or so wide of the boat, and then lean over and pull the boat up to it. That is not so easy, but you will learn the wrist motion in time. When all this comes like second nature, you will feel that you have become a part of the punt, or rather that the punt has taken life and become a part of you.