The Material used in Exposition

181.	The Material used in Exposition. The material used in amplifying or setting forth the meaning of general terms, processes, etc., is of six principal kinds, illustrations of which are given below.
1. Definition. We may explain an idea by defin¬ing it.
"History is past politics."
SUGGESTION.—What is the term defined ?
2.	Repetition. We may explain an idea by restat¬ing it from a slightly different point of view. It may, for instance, be restated in more general or more particular terms.
"Nature is an endless combination and repetition of a few laws. She hums the well-known air through innumerable variations."
SUGGESTION.- Is the thought repeated in a more general or a more concrete form?
3.	Illustrations or instances. We may explain an idea by means of illustrations.
"She [Nature} delights in startling us with resem¬blances in the most unexpected quarters. I have seen the head of an old sachem of the forest which at once reminded the eye of a bald mountain summit, and the furrows of the brow suggested the strata of the rock."
SUGGESTION.- Find the illustration in this quotation.
4.	Analogy or comparison. One of the most effect¬ive ways of explaining an idea is to compare it with something else.
"The Gothic cathedral is a blossoming in stone sub¬dued by the insatiable demand of harmony in man. The mountain of granite blooms into an eternal flower, with the lightness and delicate finish as well as the a6rial proportions and perspective of vegetable beauty."
SUGGESTION.- Find the analogy in this extract.
5.	Classification. (See the paragraph from Bur¬roughs's Springs, § 180. We have there a paragraph made up by enumerating the different kinds of springs.)
6. Narration generalized is used sometimes in the explanation of general processes or methods. The following account of the
manufacture of flour is an example of narration generalized used in explaining a process :
"After the wheat has been cleaned, of what may be called field impurities, including cockle, it passes to graders, which separate the small, shrunken, or imper¬fect kernels from the plump and sound ones ; thus enabling the miller to keep up his higher grades of flour by using only sound wheat, while the inferior quality may be kept separate and reduced to a lower grade flour. This grading is perhaps more generally practised in mills using soft wheat exclusively than in those which use mainly hard wheat, with only a suffi¬cient mixture of soft to expedite its reduction.
The next operation is a radical one, consisting of the passing of the wheat through a machine, known as the scourer and•smutter. Crease dirt, while hardly percep¬tible to the casual observer, is peculiarly abhorrent to the good miller, and must be taken out before pure white flour can be made."
It is in books on science that we most frequently find examples of the exposition of processes. Scien¬tific exposition as well as scientific description does not properly belong to the study of literature as an art, because it aims merely at clearness of statement. Compare the description of a bird in a textbook on ornithology with Shelley's Skylark if you wish to understand the difference in method.
183. Expository Paragraphs to be Classified for Material. The material used to develop the fundamental thought in the following extracts should be classified by showing that it is repetition, definition, exemplification, analogy, classification, or narration generalized.
The following conversation between a fisherman and his pupil is taken from Walton and Cotton's The Complete Angler :
Piscator: Well, scholar, you see what pains I have taken to recover the lost credit of the poor despised chub [a kind of fish]. And now I will give you some rules how to catch him 
Go to the same hole in which I caught my chub, where, in most hot days, you will find a dozen or twenty chevens floating near the top of the water. Get two or three grasshoppers as you go over the meadow, and get secretly behind the tree, and stand as free from motion as possible. Then put a grasshopper on your hook, and let your hook hang a quarter of a yard short of the water But it is likely the chubs will sink down towards the bottom of the water, at the first shadow of your rod — for the chub is the fearfullest of fishes,— and will do so if but a bird flies over him and makes the least shadow on the water. But they will presently rise up to the top again and there lie soaring till some shadow affrights them again. I say, when they lie on the top of the water, look out the best chub— which you, setting yourself in a fit place, may very easily see,—and move your rod as softly as a snail moves to that chub you intend to catch.
To punish a man because he has committed a crime, or because he is believed, though unjustly, to have committed a crime, is not persecution. To punish a man because we infer from the nature of some doctrine which he holds, or from the conduct of other persons who hold the same doctrines with him, that he will com¬mit a crime, is persecution, and is, in every case, foolish and wicked.
Iv.
The more we study the body and the mind, the more we find both to be governed, not by, but according to laws, such as we- observe in the larger universe.— You think you know all about walking,— don't you, now? Well, how do you suppose your lower limbs are held to your body ? They are sucked up by two cupping ves¬sels (" cotyloid "— cuplike — cavities), and held there as long as you live, and longer. At any rate, you think you move them backward and forward at such a rate as your will determines, don't you ? On the contrary, they swing just as any other pendulums swing, at a fixed rate determined by their length. You can alter this by muscular power, as you can take hold of the pendulum of a clock and make it move faster or slower ; but your ordinary gait is timed by the same mechanism as the movements of the solar system.
- OLIVER WENDELL HOLMES,
The Autocrat of the Breakfast Table.