LESSONS FOR LEARNERS.
PRACTICAL GEOMETRY.
We will not commence our instructions with the hackneyed “definitions,” but give our readers full credit for the knowledge of what is a point, a right or straight line, a curved line, parallel lines—and so forth, and proceed at once to practice.
There are some persons who think that with a drawing-board and square, they can, without fail, make all sorts of horizontal, perpendicular, or parallel lines, and that therefore any geometrical rules for such purpose are to them unnecessary. But, suppose the drawing-board, or the square is absent, or that neither can be had. In such an emergency the want of the following items of knowledge would be severely felt, and, therefore, the acquirement and retention of them is something desirable, and even highly necessary.
Problem I. To erect a perpendicular on a given right line.
Fig. 1
A, B, is the given right line. From the point C, with a radius longer than the perpendicular distance describe the arc, or part of a circle, D, D. And from the points of intersection with the right line A, B, describe arcs cutting each other at C and E. Join C and E, and the perpendicular is obtained on either side of the right line A, B.
Problem II. To erect a perpendicular at the middle of a right line.
From the extreme points of the right line A, B, with radii less than the length of the line describe two arcs intersecting each other at C and D, and through the points of their intersection draw the line, which will be perpendicular to the given right line at the middle.