Pantometria — A Geometrical Treatize of Measuring

The First Book

Of straight-lined angles there are three kinds: the orthogonal, the obtuse, and the acute angle.

When any right line falls perpendicularly upon another—that is to say, making the angles on either side equal—each of those angles is an orthogonal or right angle, and that falling line is a perpendicular.

Geometric diagram showing a vertical line (AB) intersecting a horizontal line (DC) at right angles. The vertical line is labeled "A Perpendicular" and the angle at point A is labeled "A right angle".

B A C the right angle contained by the perpendicular and one part of the ground line, equal to B A D the right angle contained by the perpendicular and the other portion of the ground line; and therefore, both are orthogonal.

The broad or obtuse angle is greater than the orthogonal.

A diagram of an obtuse angle (greater than 90 degrees) with the vertex pointing down and to the right.

The acute or sharp angle is lesser than the right angle.

A diagram of an acute angle (less than 90 degrees) with the vertex pointing to the right.

A figure is comprehended within limits and bounds, whether it be one or many.

A circle is a plain figure determined with one line, which is called a circumference, in whose middle there is a point named its center. From this point, all right lines drawn to the circumference are equal.

A circle with a central point. The word "circumference" is broken into parts and placed around the exterior of the circle: "A" at the top, then "cir", "cum", "f", and "rens." A label "A circle" is written inside.