Abbreviations, p. 6.

Addendo, 240.
Algebraic sum, 110.
Alhazen's Problem, 326.
Alternando, 237.

Altitude of a triangle, 74.
of a parallelogram, 280.

Analysis, 221.

Angle between two circles, 361,
a line and a circle, 361.

Angles, def. of, 2.

measurement of, 25.
arms, sides, vertex of, 2.

acute, 51.

obtuse, 51.
right, 15.

alternate, interior, exterior, 31.
Antecedents of ratios, 233.
Antisimilitude, rectangle of, 341.
circle of, 345.

Arcs, def. of, 122.

major and minor, 149.

Area, 2.

Axiom, def. of, 1.

on the intersection of lines, I.
on the intersection of two circles, 3.
on the equality of two magni-
tudes to a third, 3.

on the addition of equals to
equals, 3.

on the subtraction of equals from
equals, 4.

on the coincidence of figures, 9.
involved in the defs. of a straight

line and circle, 23.

on the condition of parallelism, 31.
on the contact of circles, 126.
on the coincidence of arcs, 147.
on the bisection of a circumfer-

ence by a diameter, 152.

on images, 313.

Axis of similitude, 343.
of perspective, 331.

Base of a triangle, II and 47.
Brahmegupta's Theorem, 168.
Brianchon's Theorem, 377..

Casey's extension of Ptolemy's
Theorem, 391.

Castillon's Problem, 382 and 383.
Central axis, 348.

Centre, of a circle, 3.

of an equilateral triangle, 74.

of mean position, IIO.

of similarity, 253 and 283.
of similitude, 339.

of perspective, 331.

Centroid, 70.

Ceva's Theorem, 328.

Chapple's Theorem, 295.
Chord, 122.

Circle, def. of, 3.

centre and radius of, 3.
circumference of, 3.

diameter of, 122.
Circum-centre, 72.
Circumscribed polygons, 193.
Co-axal circles, 348.
Collinear points, 69.
Commensurable, 230.

Common tangents to two circles:
construction to draw, 226.

direct and transverse, 340.
Complement of an angle, 15.
Complements of parallelograms, 45.
Complete quadrilateral, def. of, 299.
harmonic properties of, 370.
Componendo, 238.
Compound ratio, 243.