Page:Euclid's Elements 1714 Barrow translation.djvu/14

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X. When a right line CG tanding upon a right line AB, makes the angles on either ide thereof, CGA, CGB, equal one to the other, then both thoe equal angles are right angles; and the right line CG, which tandeth on the other, is termed a Perpendicular to that (AB) whereon it tandeth.

Note, When everal angles meet at the same point (as at G) each particular angle is decribed by three letters; whereof the middle letter heweth the angular point, and the two other letters the lines that make that angle: As the angle which the right lines CG, AG make at G, is called CGA, or AGC.



XI. An obtue angle is that which is greater than a right angle; as ACD.

XII. An acute angle is that which is les than a right angle; as ACB.

XIII. A Limit, or Term, is the end of any thing.

XIV. A Figure is that which is contained under one or more terms.

XV. A Circle is a plain figure contained under one line, which is called a Circumference; unto which all lines drawn from one point within the figure, and falling upon the circumference thereof, are equal the one to the other.



XVI. And that point is called the Center of the Circle.

XVII. A Diameter of a circle is a right line drawn through the center thereof, and ending at the circumference on either ide,