Exposition a Familiar Kind of Composition

Your textbook in science, whether you are studying physiography, biology, physics, or chemis¬try, uses exposition almost exclusively. It consists largely of definitions, classifications, and the expla¬nation of general processes. Your English, Latin, French, or German grammar also contains ex¬amples of this kind of discourse which deal with definitions, classifications, and enumerations.--A The definitions of terms and the explanations of mathe¬matical processes found in your algebra are also examples of exposition. You can mow see that this form of composition is not something very new and difficult. It is, in fact, the form you use more fre¬quently than any other in the schoolroom. The
recipes in the family cook-book, and the directions which accompany Butterick's patterns, are homely examples of exposition.
Not only have you studied textbooks which make use of formal exposition, but you have very proba¬bly used this type of discourse many, many times informally in conversation with your friends. The following is an example of colloquial exposition :
"So you have invented another 'scope, have you ? Let me see ! there is the microscope, telescope, and now what's this new 'scope ? "
"The spectroscope is an instrument for forming and examining spectra ; particularly those produced -by flames in which different substances are volatized so as to determine the composition of the substances."
"Well, that description is just about as clear to me as your 'scope itself," said the dwarf.
"Well, now, you see this prism I hold in my hand, which is made of clear glass, and has three rectangular plain faces, or sides, and two equal triangular ends. Now look at the light through it. What do you see ? "
"All the colors of the rainbow," exclaimed the dwarf.
"Just so," said the giant ; "a ray of light passed through the prism, and falling on a white screen, will show the seven colors of the rainbow. Now scientists have found that the light from the flames of certain metals, passing through prisms arranged in a certain way, will throw particular colors upon a screen ; and putting this in practice they have formed the spectro¬scope containing several glass prisms, which, combined with a telescope, enables them to catch the rays of light from the planets, and so decompose them as to get differ¬ent colors reflected ; and knowing what colors the flames of certain metals will produce, they thus determine what - metals are to be found in those distant worlds."
- LYDIA H. FARMER, A Story Book of Science.
This quotation is an example of exposition be¬cause it explains a class-name — the spectroscope.