Radius, the, of the earth's orbit, 218.

Rasis. _See_ Rhazes.

rays of magnetick virtue, 95.

Reinoldus, Erasmus (or Rheinholdus), 213.

_remora_, the (or sucking fish), 7, 63, 110.

resin becomes electrical by friction, 48, 52.

respective points, 5, 153, 161, 162.

reversal of polarity, 101, 137.

revolution of the globe, 46, 81, 91, 220.

repulsion, electrical, denied to exist, 113.

Rhazes (Muhammad ibn Zakar[=i]y[=a]), 34, 35.

rings, on the verticity of, 129.

Rodriguez de Lagos, 177.

Rosetius Calaber, Hannibal, 3.

Ruellius, Joannes, 7.

Rueus, Franciscus (de la Rue), 6.

Saffron of Mars, 34, 91, 93.

sagda, or sagdo, the, 111.

Sanuto, Livio, 5, 153, 167.

sapphire, the, 48.

scales of iron, 22.

Scaliger, Julius Caesar.

on cause of magnetick direction, 5, 64, 153.

on a fall of meteorick iron, 26.

on preservation of loadstones, 37.

on amber, 47.

on magnetick attraction, 70.

admits the loadstone to have a soul, 68.

on diamond attracting iron, 112.

scoria or slag of iron, 34, 35.

sealing wax is electrical, 48, 53.

Sebastian Cabot. _See_ Cabot.

Serapio, or Serapio Mauritania (Yuhanna ibn Sarapion), 2, 6.

Severtius, Jacobus, 5.

shielding, magnetick, by iron plate, 83, 85.

{246} _siderites_ ([Greek: siderites]) 8, 11, 143.

_siegelstein_ 11.

silk suspension for magnetick iron, 29, 30.

Silvaticus, Matthaeus, 3.

silver, loadstone for, 109, 110.

similars, doctrine of attraction of, 50, 62.

Simon Stevinus, *v _bis_, 167, 168.

slate, magnetick properties of, 43.

smeargel (emery), 22.

Solinus, Caius Julius, 1, 9, 111.

Solomon the King, 4.

Sotacus, 9.

Stadius, 213.

stars are at various distances, 215.

steel, 23, 39, 69, 71, 93, 95, 147.

Stevinus, Simon, *v _bis_, 167, 168.

_stomoma_ ([Greek: stomoma]) 23, 33, 36.

Strabo, 25.

_succinum_. _See_ amber.

Sudini, or Sudavienses, 47.

sulphur, electrical by friction, 48, 53, 56, 59.

[Greek: sundrome], *vj.

[Greek: sunentelecheia], 68.

Sussex, iron ore in, 22.

sympathy and antipathy, 65, 68, 112.

Tacitus, Cornelius, 25.

Taisner, or Taisnier, Joannes, 5, 107.

Tariassiona or Tarazona, 23.

terrella.

definition of, *vj, 12, 13.

poles and axis of, 13, 72, 81, 144.

divided into two parts, 72.

magnetick vigour, diagram of, 74, 75.

how small pieces of iron behave toward, 75, 76.

orbe of virtue of, 76, 77, 104.

"geography" of, 78.

aequinoctial circle of, 79, 144.

parallels of, 80, 211.

magnetick horizon of, 80.

proportion of the forces in, 81, 82.

experiment with iron sphere, 85.

small iron sphere and rod, 94, 102.

centre of magnetick virtue in, 95.

irregular terrella to exhibit variation, 155, 157.

to illustrate the dip of the needle, 190, 192.

analogy of, with the earth, 41, 78, 119, 211.

testing loadstones, methods of, 108.

Thales of Miletus, 11, 61, 68, 208, 210.

_theamedes_, the, 18.

Thebitius, or Thebit ben Korrah, 117, 236.

Themistius, 71.

Theophrastus, 1, 9, 11.

Thomas Aquinas, 3, 64.

tides, the cause of, 86.

Tycho Brahe, 174, 229.

Variation of the compass, 7, 46, 79, 116, 151-163, 166, 167, 180.

variation at the Azores, 4, 154, 156, 167.

versorium, magnetick, definition of, *vj.

use of, 13, 115, 147.

versorium, non-magnetick, use of, 48, 49, 50.

verticity, 28, 115, 119-147.

acquired, 67, 68, 84, 85, 104, 123, 125, 129, 138, 139, 141, 142, 211.