Page:An introduction to linear drawing.djvu/31

10 SECOND CLASS. 1.Make two triangles of perpendicular sides.

After having made one angle, the pupil will draw a perpendicular to one of the sides, and then a perpendicular to the other side, until the perpendiculars cross each other.

One of the angles is acute, and the other obtuse; and if you lengthen one of the perpendiculars, a new angle will be formed exactly like the angle first made, as the dotted continuation of the perpendicular in fig. 1 shows.

2.Make two triangles of perpendicular sides.(fig.2.)

Make one triangle, and then draw a perpendicular to each side, until the perpendiculars touch and form angles. Each side of each triangle must be perpendicular to some side of the other triangle.



3.Make a trapezoid.(fig. 3.)

A trapezoid has four sides, of which, two, called the bases, are parallel. In the figure, these are the upper and lower sides. The height is a perpendicular from base to base. As this figure is easily made, the length of the bases and the height may be given: thus, "Make a trapezoid whose height shall be one inch,and whose bases shall be an inch and a half and two inches." When no two of the sides are parallel the figure is called a Trapezium.