Harmonic points, 29, 31, 32, 33, 34, 35, 36, 43, 71, 161

Harmonic tangents to a conic, 91, 92

Harvey (1578-1657), 169

Homology, 180, 182

Huygens (1629-1695), 162

Hyperbola, 110, 111, 113, 114, 115, 116, 117, 118, 162

Imaginary elements, 146, 180, 181, 182, 185

Infinitely distant elements, 6, 9, 22, 39, 40, 41, 104, 107, 110

Infinity, 4, 5, 10, 12, 13, 14, 15, 17, 18, 19, 20, 21, 22, 41

Involution, 37, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 161, 163, 170

Kepler (1571-1630), 162

Lagrange (1736-1813), 176, 179

Laplace (1749-1827), 179

Legendre (1752-1833), 179

Leibniz (1646-1716), 173

Linear construction, 40, 41, 42

Maclaurin (1698-1746), 177, 178

Measurements, 23, 40, 41, 104

Mersenne (1588-1648), 168, 171

Metrical theorems, 40, 104, 106, 107, 141

Middle point, 39, 41

Moebius (1790-1868), 179

Monge (1746-1818), 179, 180

Napier (1550-1617), 162

Newton (1642-1727), 177

Numbers, 4, 21, 43

Numerical computations, 43, 44, 46

One-to-one correspondence, 1, 2, 3, 4, 5, 6, 7, 9, 10, 11, 24, 36, 87, 43, 60, 104, 106, 184

Opposite sides of a hexagon, 70

Opposite sides of a quadrilateral, 28, 29

Order of a form, 7, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21

Pappus (fourth century A.D.), 161

Parabola, 110, 111, 112, 119, 162

Parallel lines, 39, 41, 162

Pascal (1623-1662), 69, 70, 74, 75, 76, 77, 78, 95, 105, 125, 162, 169, 171, 172, 173

Pencil of planes of the second order, 59

Pencil of rays, 6, 7, 8, 23; of the second order, 57, 60, 79, 81

Perspective position, 6, 8, 35, 37, 51, 53, 71

Plane system, 16, 23

Planes on space, 17

Point of contact, 87, 88, 89, 90

Point system, 16, 23

Point-row, 6, 7, 8, 9, 23; of the second order, 55, 60, 61, 66, 67, 72

Points in space, 18

Pole and polar, 98, 99, 100, 101, 138, 164, 166

Poncelet (1788-1867), 177, 179, 180, 181, 182, 183, 184

Principal axis of a conic, 157

Projection, 161

Protective axial pencils, 59

Projective correspondence, 9, 35, 36, 37, 47, 71, 92, 104

Projective pencils, 53, 64, 68

Projective point-rows, 51, 79

Projective properties, 24

Projective theorems, 40, 104

Quadrangle, 26, 27, 28, 29

Quadric cone, 59

Quadrilateral, 88, 95, 96

Roberval (1602-1675), 168

Ruler construction, 40

Scheiner, 169

Self-corresponding elements, 47, 48, 49, 50, 51