angles, the triangle A is called an orthigonium, or right-angled scalenon, because its angle at the point D is a right angle. Also, the triangle B is called an ambligonium, or an obtuse-angled scalenon, because its angle at the point I is a blunt or obtuse angle. And lastly, the triangle C is called an oxigonium, or an acute-angled scalenon, because all its angles are acute or sharp. It is to be noted generally in all triangles, that in comparison of any two sides of a triangle, the third side is called the base; as of the triangle A, in respect of the two lines E-D and E-F, the line D-F is the base; in regard of the two lines F-D and F-E, the line E-D is the base; and in respect of the two lines D-E and D-F, the line E-F is the base.

DEFIN. XXIV.

A square, or quadrat, is a four-sided figure, whose sides are all equal, and angles all right angles.

Euclid, Book 1, Def. 30. Ramus, 12. 2. 2. Con. 1.

A geometric diagram of a square with vertices labeled A and B at the top, and C and D at the bottom.
As the figure A-B-C-D is a square, or quadrat, because all the lines thereof are equal, and all the angles are right angles. These four-sided figures likewise, as well as triangles, take their name partly from their sides and partly from their angles, as by their several definitions hereafter appears.

DEFIN. XXV.

A long square is that whose angles are all right angles, and whose opposite sides only are equal.

Euclid, Book 1, Def. 31. Ramus, 1. 13.

A geometric diagram of a rectangle ("long square") with vertices labeled A and B at the top, and C and D at the bottom. The horizontal side AB is longer than the vertical side AC.
This figure differs little from the square, or quadrat, last defined, having all equal angles like it; but the sides are unequal. As in this figure A-B-C-D, all the angles are right angles, and the opposite sides only are equal, as the length A-B is equal to the length C-D, and the breadth A-C to the breadth B-D; but compare them otherwise, and they are unequal.

DEFIN. XXVI.

A rhombus (or diamond) is a figure with four equal sides, but no right angle.

Euclid, Book 1, Def. 32. Ramus, 8. 14.

As this figure A-B-C-D is a rhombus, having all its sides equal, and likewise the opposite angles; but the angles at A and D are acute angles, and those at B and C are obtuse. Between a square, or quadrat,