In Mechanical Drawing, Parts I to III, inclusive, the funda-mental principles were explained and illustrated. In Machine Drawing, Parts I and II, the production of working drawings has also been discussed to some extent, and the usual characters and symbols explained and applied. The elementary work already outlined has been treated chiefly from the standpoint of correctness of line representation considered by itself, without a detailed study of the use to which the drawings so produced are to be applied.

Evidently this is the proper method, for the student should gain a thorough understanding of the principles which underlie line representation before attempting to apply them to any extended practical use. In all of this preceding work it was intended that the theoretical principles should overshadow any incidental references made to practical application, however true and pertinent the latter may have been for purposes of illustration. Hence, before taking up any advanced work, the student should fully realize the importance, in fact, the absolute necessity, of thoroughly understanding the fundamental principles which have been outlined in the preceding books.

At this point the student must realize that a lack of proper elementary and fundamental training will make him "go lame" at every point of his course, and probably prevent the attainment of proficiency which otherwise would naturally and almost instinctively come with advanced study. It is thorough and ready knowledge, always at his fingers' ends, of all the principles of Mechanical Drawing, which makes the expert draftsman.