A puncture can be made near the top and, when a new drawing or blue-print is inserted in this cylindrical case, a cardboard tag can be looped through the puncture. This label will give the title and number of drawings in that case.
A manuscript book methodically and neatly kept should tell immediately the number of the drawing and the case.
[Fig. 293] is good for practice in line drawing and also as an optical illusion. “You look and are deceived. At first glance you say, ‘Of course, those two lines are curved.’ You are mistaken. They are exactly parallel. In order to prove this hold them up edgewise to the eye. It is, of course, the subsidiary lines which lead the vision astray. It is a case of first impressions being quite wrong.”
Fig. 295.
Linear Perspective.
It should be mentioned that this subject is outside the limits of mechanical drawing, which only deals with objects that can be measured, projected or dimensioned to an accurate scale.
But, in rounding out the more formal subjects it is well to look a little outside the rigid lines of mechanics into the methods of nature, for no system of teaching drawing is complete that does not include some explanations for sketching from nature—the objects being always around the student, the eye always clear to see and the hand only needing the training to make permanent the impressions received.
The word perspective means to see through; the word perspective being derived from the Latin word perspicere, to look through, hence, perspective is a science which teaches us to see correctly and enables us to represent the appearance of anything we may wish to draw; care should be taken in perspective drawing, to select objects interesting in themselves, and the best specimens of their class, so as to cultivate taste, while they at the same time afford useful and instructive drawing lessons.