Separation of elements in involution, 148

Separation of harmonic conjugates, 38

Sequence of points, [49]

Sign of segment, [44], [45]

Similarity, [106]

Skew lines, [12]

Space system, [19], [23]

Sphere, [21]

Steiner (1796-1863), [129], [130], [131], 177, [179], [184]

Steiner's construction, [129], [130], 131