Acute angle, 11.
Adjacent, angles, 8.

polygons, 194.

The numbers refer to pages

Angle, 6.

acute, 11.

cosine of, 416.
dihedral, 284.

in an arc, 111.

obtuse, 11.
polyhedral, 296.

reflex, 12.
right, 9.

sine of, 416.
spherical, 380.
straight, 12.

tangent of, 416.
trihedral, 296.
Angles, adjacent, 8.
alternate, 62.

complementary, 67.
supplemetary, 11.
of a triangle, 7.
vertical, 8.
Apothem, 239.

Arc of a circle, 100.
length of, 245.
Arcs, similar, 249.
Area, 195, 245, 394.
Axiom, 16.

Axis, of a circle, 372.

Axis, radical, 170.
of symmetry, 88.

Centroid of a triangle, 80.

Chord, of a circle, 100.

of contact, 119.
Circle, 14.
arc of, 100.
centre of, 14.
chord of, 100.
diameter of, 14.
radius of, 14.
secant of, 115.
sector of, 101.
segment of, 101.

tangent of, 116.

Circles, coaxial system of, 170.
concentric, 18.

in contact, 130.
Circular, cone, 361.
cylinder, 354.

Circumference of a circle, 244.

Circumscribed figure, 119.

Closed surface, 310.

Coaxial circles, 170.

Commensurable magnitudes, 141.
Common tangents, direct and in-

verse, 133.

Concentric, circles, 18.

spheres, 370.
Concurrent lines, 79.

Decagon, 233.
Diagonal, 71.

Diagonals, principal, 252.
Diameter, 14.

Dihedral angle, 284.

plane angle of, 285.

Figures, identically equal, 9.

isoperimetric, 228.

symmetrical, 88.

Frustum, of a cone, 365.

of a pyramid, 328.

Great circle, 371.

Harmonic division, 186.

Hexagon, 233.

principal diagonals of, 252.

Hexahedron, 311.

Homologous sides, 30.

Hypotenuse, 44.

Icosahedron, 311.

Incommensurable magnitudes, 141.

Indirect proof, 47.

Inscribed figure, 111.
Inverse points, 88.

Isoperimetric figures, 228.
Isosceles, triangle, 22.

trihedral angle, 302.

Length of an arc, 245.

line, 53.

to a plane, 275.

Dodecagon, 233.

Dodecahedron, 311.

Equilateral triangles, 22.

Extreme and mean ratio, 177.
Extremes, 149.

Line, oblique to a plane, 266.

parallel to a plane, 266.
perpendicular to a plane, 266.
straight, 3.

Line-segments, 3.

Lines, concurrent, 79.

parallel, 61.

perpendicular, 9.

skew or gauche, 271.

Mean proportional, 152.
Means, 149.

Measure, 140.

Median of a triangle, 79.

Minimum value, 111, 226.

Multiple, 140.

Octagon, 233.

Octahedron, 311.

Orthocentre of a triangle, 83.

Parallel, lines, 61.
planes, 266.
Parallelepiped, 317.
rectangular, 317.
right, 317.

Parallelogram, 74.

altitude of, 197.

Pentagon, 233.

Pentahedron, 311.

Perimeter, 79.

Perpendicular, to a line, 9.
to a plane, 266.

Plane surface, 4.
Points, concyclic, 114.
inverse, 88.

Polar spherical triangles, 387.
Poles of a circle, 372.

Polygon, 71, 73.

convex, 71, 73.
diagonal of, 71.

opposite sides of, 72.

perimeter of, 79.

regular, 233.

spherical, 382.

Polygons, adjacent, 194.

mutually equiangular, 161.

similar, 161.

Polyhedral angle, 296.

Polyhedral angles, symmetrical, 297.
Polyhedron, 310.

circumscribed, 378.

Polyhedrons, similar, 339.

Postulate, 15.

Principle of continuity, 125.

Prism, 311.

truncated, 315.

Problem, 17.

Projection, 212, 292.

Proportion, 149.

Pyramid, 328.

Quadrant, 372.
Quadrilateral, 73.

Radical axis, 170.
Radius, 14.

Ratio, 142, 144, 148.

extreme and mean, 177.
Rectangle, 74.

Regular polygon, 233.

apothem of, 239.

centre of, 239.

radius of, 239.

Regular pyramid, 328.

slant height of, 328.
Regular polyhedron, 342.
Rhombus, 74.

Right angle, 9.

Right triangle, 44.

Right circular, cone, 362.
cylinder, 354.

prism 311.

Scalene triangles, 22.
Secant of a circle, 115.
Section of a surface, 310.
Sector, of a circle, 101.

of a sphere, 406.
Segment, of a circle, 101,

of a sphere, 401.

Semicircle, 101.

Similar, arcs, 249.

polygons, 161.
polyhedrons, 339.
sectors, 250.
segments, 249.

Sine of an angle, 416.
Sphere, 370.
Spherical, angle, 380.

excess, 391.

polygon, 382.

pyramid, 406.

sector, 406.

segment, 401.

triangle, 382.

unit of surface, 397.

Square, 74.

Surface, closed, 310.

conical, 361.

cylindrical, 353.

plane, 4.

Symmetrical, figures, 88.
polyhedral angles, 297.
spherical triangles, 384.
Symmetry, axis of, 88.

Tangent, of an angle, 416.

to a circle, 116.
to a cone, 362.

Tangent, to a cylinder, 355.

to a sphere, 375.

Tangents, common, direct and in-
verse, 133.

Tetrahedron, 311.

Theorem, 17.

Third proportional, 152.

Transversal, 62.

Trapezium, 74.

Trapezoid, 74.

isoceles, 77.
Triangle, 5.

altitude of, 198.

centroid of, 80.

equilateral, 22.
isosceles, 22.
median of, 79.
right, 44.
scalene, 22.

spherical, 382.

Trihedral angle, 296.

isosceles, 302.

Truncated, prism, 315.
pyramid, 328.

Vertex, 5, 71, 310.

Volume of a polyhedron, 315, 324.

Zone, 401.