Aids in Gaining Clearness
Clearness then, through centralization, is the all-important necessity of expositions of this type. To aid in gaining this quality you will do well to avoid technical terms, as has already been mentioned. You can make use of graphic charts when they will be useful, so long as they are not merely a lazy device for escaping the task of writing clearly. Some machines, such as the printing press or the rock drill, defy explanation without charts and plates. Textbooks often wisely make use of this device. You can also use familiar illustrations, as the one here used of the reaper and binder or the one likening Brooklyn Bridge to a letter H with the sides far apart, the cross piece extended beyond the sides, and a cable looped over the tops of the sides. Such illustrations at the beginning of the whole or sections are useful in helping the reader to visualize. Another important aid to clearness is to take care that nothing is mentioned for which the way has not been prepared. Just as in a play we insist that the action of a character be consistent, that a good man do not suddenly commit wanton murder, and that the villain do not suddenly appear saintly, so we rightly demand that we be not suddenly confronted with a crank, wheel, office, or step in a process which bewilders us. You ought to write so that your reader will never pucker his brow and say, "What is this?" And when a detail has some special bearing, introduce it at the significant point. To have told little Johnny in the beginning that he must keep his chemicals away from flame would have avoided explosion and death; to declaim loudly after the explosion is of no value. And finally, from a purely rhetorical standpoint, make careful transition from section to section so that the reader will know exactly where divisions occur, and make liberal use of summaries whenever they may be useful without being too cumbersome.
Notice how, in the following paragraph, the writer has given the gist of the machines so that, if he wishes to expand and make a full treatment, he will still have a nucleus which will considerably facilitate the reader's understanding.
Continuous dredges are of four types—the ladder, the hydraulic, the stirring, and the pneumatic dredges. The ladder dredge excavates the bottom by means of a series of buckets running with great velocity along a ladder. The buckets scrape the soil at the bottom, raise the débris to the surface and discharge it into barges or conveyors so as to send it to its final destination. The hydraulic dredge removes the material from the bottom by means of a large centrifugal pump which draws the materials, mixed with water, into a suction tube and forces them to distant points by means of a long line of pipes. The stirring dredges are those employed in the excavation of soils composed of very finely divided particles; they agitate the soils and the material thus brought into suspension is carried away by the action or current of water. The pneumatic dredges are those in which the material from the bottom is forced into the suction tube and thence into the discharging pipe, by the action of continuous jets of compressed air turned upward into the tube.[60]
Notice also the care with which the author of the paragraph which follows and explains the phonopticon states early in his treatment the scientific basis for the operation of the machine, without knowing which a reader would be hopelessly confused to understand how the machine could possibly do what the author says it does.
The element selenium, when in crystalline form, possesses the peculiar property of being electro-sensitive to light. It is a good or bad conductor of electricity according to the intensity of the light that falls upon it, and its response to variations of illumination is virtually instantaneous.
This interesting property has been utilized in a wide variety of applications, ranging from the transmission of a picture over a telegraph line to the automatic detection of comets; but by far the most marvelous application is that of the phonopticon.... It is an apparatus that will actually read a book or a newspaper, uttering a characteristic combination of musical sounds for every letter it scans.
The principle of operation is not difficult to understand. A row of, say, three tiny selenium crystals is employed, each crystal forming part of a telephone circuit leading to a triple telephone-receiver. In each circuit there is an interrupter that breaks up the current into pulsations, or waves, of sufficient frequency to produce a musical note in the receiver. The frequency differs in the three circuits, so that each produces its characteristic pitch. Although the conductivity of selenium is increased by intensifying its illumination, the electrical connections in this apparatus are so chosen that while the crystals are illuminated no sounds are heard in the telephone, but when the crystals are darkened, there is an instant audible response.
The apparatus is placed upon the printed matter that is to be read, with the row of crystals disposed at right angles to the line of type. The paper directly under the crystals is illuminated by a beam of light. This is reflected from the unprinted part of the paper with sufficient intensity to keep the telephone quiet, but when the crystals are moved over the black printing, the light is diminished, and the crystals lose their conductivity, causing the telephone to respond with a set of sounds which vary with the shape of the letter. Suppose the apparatus was being moved over the letter V, the upper crystal would encounter the letter first, then the middle one would respond, next the lower one would come into action for an instant, followed by a second response of the middle crystal and a final response of the upper crystal. A set of notes would be sounded somewhat after this fashion: me, re, do, re, mi. The sound combination with such letters as S and O is more complicated but it is distinguishable. When we read with the natural eye we do not spell out the words letter by letter, but recognize them by their appearance as a whole. In the same way with the mechanical eye entire words can be recognized after a little practice.
Of course the phonopticon is yet in the laboratory stages, but it offers every prospect of practical success, and its possibilities are untold. It is quite conceivable that the apparatus may be elaborated to such an extent that a blind man may see (by ear) where he is going. His world may never be bathed in sunshine, but he may learn to admire the beauties of nature as translated from light into music.[61]