Cognition is not complete until the knowledge has been or can be applied. At times there may be a division of labor and glory in the discovery and application of truth. The discoveries of Professor Henry which made the electric telegraph possible involved thinking quite as valuable as the invention of Professor Morse. The achievement of Cyrus W. Field in laying the Atlantic cable involved thinking quite as important as the researches and experiments of Lord Kelvin which made the cable successful. Interesting examples of such division of labor in thinking cannot justify neglect of the applications after a general truth has been evolved and stated.
The instruction may sometimes begin with a statement of applications, in order to prepare the mind for the thinking that issues in knowing. The applications of color in the railway service, in navigation, and in the arts will create an interest in the study of color without which the presentation of the fundamental ideas may be in vain. Several lecturers have admitted that they failed, in the presentation of color lessons, to hold the attention of their pupil-teachers until they excited an interest in color by indicating important applications. This statement of applications by way of preparation must, however, not be confounded with the applications which should follow the framing of general propositions and the cognition of general truths.
The hypotheses of the scientist correspond to the general truths and principles which instruction always aims to reach. In all except the most advanced investigations, the pupil should work under the guidance of principles that have risen above the hypothetical stage. He should think under the inspiration of well-established truths. He should master the known in his chosen field before he seeks to enlarge the boundaries of human knowledge by invasions into the realm of the unknown. Sad is the spectacle of a talented mind wasting its strength in fruitless efforts to rediscover what is already well established.