columns, 114.

Refraction explained, 175.

Resin, soot of, used to make black, 218.

Resonant sites of theatres ([Greek: antechountes]), 153.

Retaining walls, 190 _f._

Reticulatum opus, 51.

Retrogression of planets, 261.

Rhine, 231.

Rhodes, 55 _f._, 167, 219, 220;
length of shadow of gnomon at, 270;
siege of, 316 _f._

Rhone, 231.

River (constellation), 268.

Rivers rise in the north, 231.

Rome, 63, 64, 78, 80, 145, 217;
site of, determined by divine intelligence, 174;
length of shadow of gnomon at, 270.

Romulus, hut of, 40.

Roofs, of mud, 39 _f._;
timbers of, 107;
of Tuscan temples, 122;
of circular temples, 124.

Rooms, proportions of, 176 _ff._;
proper exposure for, 180 _f._;
should be suited to station of the owner, 181 _f._

Round Building at Delphi, 198.

Salmacis, spring of, 54.

Salpia in Apulia, 21.

Sambuca illustrates effect of climate on voice, 171.

Samos, 12, 103, 263, 269, 273;
Doric temple of Juno in, 198.

Sand, 44 _f._, 48.

Sandarach, 214; made from white lead, 219.

Sardis, 53.

Sarnacus, 199.

Saturn (planet), 260, 261, 262.

Satyrus, 199.

Scaena of theatre, 146;
dimensions of, 148;
scheme of, 150;
decorations of, 150;
of theatre at Tralles, 212.

Scale, musical, 141.

Scaling machine, 311.

Scamilli impares, 89, 155, 320.

Scaphe (sun dial), 273.

Scopas, 199.

Scopinas, 12, 273.

Scorpion (constellation), 266.

Scorpiones, rules for making, 303 _ff._

Scotia, 90, 112.

Scutula of ballistae, 306 _f._

Seats in theatre, dimensions of, 148.

Selinusian chalk ([Greek: isatis]), 220.

Semiramis, 235.

Senate house, location of, 137.

Septentriones (She-Bears), 267.

Septimius, P., 199.

Serapis, site of temple of, 31.

Serpent (constellation), 266.

Serpent-holder (constellation), 266.

Sesterce, 74.

She-Goat (constellation), 266.

Ship, motion of, explained, 291.

Shipyards, 164.

Sicily, 236.

Siege machines, 309 _ff._

Signinum work, 247 _f._

Signs of the Zodiac, 258;
sun's course through, 264 _f._;
shown on dials, 276 _f._

Silanion, 199.

Silenus, on the proportions of Doric structures, 198.

Simae ([Greek: epaietides]), 96, 108.

Sinope, 214.

Smyrna, 197, 214;
Stratoniceum at, 154.

Snake (constellation), 268.

Socrates, 69, 70, 195.

Soli, 235.

Soracte, stone quarries of, 49.

Sounding vessels in the theatre, 143 _ff._

Southern Fish (con