Page:An introduction to linear drawing.djvu/24

 In making horizontal lines, the pupil should make them parallel to the top or bottom of his slate or paper, and in making perpendiculars they should be parallel to the sides of the slate or paper. Parallel lines are lines running in the same direction equally distant from each other in every part; thus, the horizontal lines in figures 1, 2, 3, 4, are parallel to each other. Lines may be drawn parallel at any distance from each other.

18. Draw two parallel horizontal lines, then three, four, five and six.

14. Draw two parallel perpendiculars, then three, four, five and six.

15. Draw an oblique line and cut it into two, four, three and six parts.

An oblique line is one between a horizontal and a perpendicular; that is, a leaning line.

16. Draw two parallel obliques, then three, four, five and six.

17. Draw parallel lines an inch apart, then half an inch, a quarter, &c.

18. Draw a perpendicular, and cut it into two, three four, five, six equal parts.

It is difficult to cut a perpendicular into equal parts, because of an optical deception which leads us to think the upper parts shorter than they really are. This must be guarded against.

19. Join two dots or points by a right line.

The pupil will move his pencil two or three times from the left dot to the right, before he draws the line. This precaution is more necessary when the operation is performed on paper than when on a slate, where it may be erased if wrong.