A DEFINITIONS. 1. Point is that which hath no parts, or which hath no mage Sec Notes. nitude. II. A line is length without breadth. III. The extremities of a line are points. IV. V. VI. VII. A plane superficies is that in which any two points being taken, See N. che ftraight line between them lies wholly in that superficies. VIII. " A plane angle is the inclination of two lines to one another See N. " in a plane, which meet together, but are not in the same IX. to one another, which meet together, but are not in the N. B. •N. B. When several angles are at one point B, any one ' of them is expressed by three letters, of which the letter that "js at the vertex of the 'angle, that is, at the point in which • the straight lines that contain the angle meet one another, is put between the other two letters, and one of these two is • somewhere upon one of those straight lines, and the other upon the other line: Thus the angle which is contained by ' the straight lines AB, CB is named the angle ABC, or CBA; that which is contained by AB, DB is named the angle ABD, or DBA ; and that which is contained by DB, CB is • called the angle DBC, or CBD; but, if there be only one angle ' at a point, it may be expreffed by a letter placed at that point ; ( as the Angle at E.' X. ther straight line makes the adjacent XI. XII. XIII. XIV. XV. OF EUCLI D. Book 1. XV. led the circumference, and is such that all straight lines XVI. 354 And this point is called the centre of the circle. XVII. A diameter of a circle is a straight line drawn through the See N. centre, and terminated both ways by the circumference. XVIII. XIX. XX. XXI. XXII. XXIII. XXIV. XXV. XXVI. Book I. ΔΔΔ XXVI. XXVII. XXVIII. A A A XXIX. XXX. equal, and all its angles right angles. XXXI. XXXII. are not right angles. XXXIII. See N. A rhomboid, is that which has its opposite sides equal to one another, but all its fides are not equal, nor its angles right angles. XXXXIV OF EUCLID. 13 Book I. XXXIV. Xxxv. which, being produced ever so far both ways, do not meet. L 1. II. III. And that a cisele may be described from any centre, at any distance from that centre. A X I OM S. TH ES, 1. 11. IV. y. VI. VII. VIII. IX. |