PARALLEL lines are said to be parallel to each other when they are throughout their whole lengths the same distance apart.
PERPENDICULAR. When one straight line, meeting another, makes the angles at the point of contact equal, each of the angles is called a right angle, and the lines are said to be perpendicular to each other. Remember especially that perpendicular and vertical have not the same meaning. Vertical means an unvarying upright position. Perpendicular means that one line or plane meets another line or plane at right angles.
The [fig. 295] on [page 246] is a study in perspective, showing a water reflection. As rays from every visible part of the object are reflected, all following the same law, the reflection will appear to the eye inverted, and of the same size as the object. The arch itself forms the upper half of a hollow cylinder, and the reflection forms the lower half. The reflection shows much more of the interior of the arch than can be seen directly. The leaning tree, the boy fishing, and the receding banks, all are seen in accordance with the laws of reflection and perspective.
THE HORIZONTAL LINE, THE POINT OF SIGHT AND THE VANISHING POINTS are the principal items. These should be studied in every room and during every walk, and the more pleasing accidents of form stored in the mind or committed to paper for future use.
Fig. 304.
OPTICS, the science of sight, gives us the following laws:
1. That we see by the agency of light.
2. That light passes from objects to our eyes.
3. That light travels in straight lines, which are called Visual Rays.