iv ; INDEX TO ASTRONOMY. 
Periods of revolution of the planets, 105. 
Perieci, the, 146. 
Persians, length of year determined by, 74. 
Phases of the moon, 83. 
Pheenicians, application of astronomy to navi- 
gation by, 74. 
Phrystus of Wittemberg, author of the first 
treatise on the solar spots, 132. . 
Planetarium, the, 171. 
Planetary system, definition of, and description 
of various, 102 ; tabular view of the most im- 
portant elements of the, 105. 
Planets, apparent course of the superior and in- 
ferior, 80; heliocentric and geocentric place 
of the, 98; commutation and annual paral- 
lax, ib.; dates of the discovery of various 
primary and secondary since the invention 
of the telescope, 104; tabular view of their 
different elements, 105; primary causes of 
the elliptical orbits of the, 114; ratio of 
their diameters to the sun’s diameter, 118; re- 
lative volumes of the sun and, 119; distance 
from the sun, and apparent diameters at times 
of greatest apogee and perigee, 120; size and 
diameter of the sun as seen from the, 121. 
Planispheres, 93. 
Points, circles, and terms in the celestial and ter- 
restrial spheres, 76-79. 
Ptolemy, his astronomical labors, 74 ; planetary 
system of, 102; supposed inventor of the tri- 
quetrum, 167. 
Quadrant, the mural, 159 ; movable, 160. 
Quadratures, the, of the moon,-83. 
Quarters of the moon, 83. 
Rectification of a transit instrument, 161. 
Refraction, 126. 
Repsold’s transit instrument at St. Petersburgh, 
161; meridian circle, 163 ; equatorial, 164. 
Roemer, inventor of the transit instrument, 160. 
Rosse’s, Lord, telescope, 159. 
Rotation, apparent, of the celestial sphere, 79 ; 
of the planets, 105. 
Rudolphian tables, the, constructed by Kepler, 75. 
Saros, meaning of the term, 84. 
Saturn, moons of, 117; ring system of, 119, 141; 
physical condition of, 148. 
Seasons, the, 85; inequality of, a necessary con- 
sequence of the elliptic motion of the earth, 
109. 
Sector, the reflecting, 167. 
Selenography, 140. 
Sextant, the reflecting, 166. 
Shooting stars, 145. 
Solstices, the, 107. 
Sosigenes, inventor of the Julian calendar, 74, 
150. 
Sphere, the armillary, 76; points, circles, and 
terms in the celestial, ib. ; and in the terres- 
trial, 79 ; apparent rotation of the celestial, ib. 
Spherical Astronomy, 76. 
654 
~ 
Spots on the sun, 131 ; Herschel’s hypothesis with 
respect to, 132; first discovered by Harriot 
132. 
Stars, the fixed, their size, number, arrangement, 
and distances, 89; divisions of, 90; maps of 
the, 93; double, 94; multiple, variable, and 
new, 96; groups of, 144; shooting, 145; 
method of finding particular, 173. 
Struve’s observations on double stars, 89 ; his 
catalogue of double and multiple stars, 94. 
Sun, daily and yearly motion of the, 85 ; eclipses 
of the, 100; the only certain method of ob- 
taining its parallax, 111; relative volumes of 
the, and planets, 119 ; size and diameter of the, 
as seen from the planets, 121; total eclipse of 
the, on June 4th, 1788, 122 ; spots on the, 131 ; 
mock, 145; possibility of its being habitable, 
147. P 
Sunday letter, the, 151. 
Sun-dials, 167. 
Superior planets, illustration of the apparent 
course of, 81. 
Surfaces of the planets, 105. 
Syzigies, definition of, 83. 
2 
Tabular view of the most important elements of 
the planetary system, 105. 
Telescopes, 155; two kinds of, refractors and 
reflectors, ib.; Galilean and common, 156 ; 
description of the Dorpat refractor, 156; re- 
flecting, 158 ; Herschei’s improvements in, 158 ; 
Lord Rosse’s, 159; meridian telescope or 
transit instrument, 160 ; equatorial, 164. 
Tellurium, the, 171. 
Terrestrial sphere, points, circles, and terms in 
the, 79. 
Theodolite, the, 165 ; two kinds of, ib. 
Tides, explanation of the, 128. 
Topography of the moon, 134. 
Transit instrument, 160. 
Transits of the inferior planets, 111 ; principal 
phases of, 121. 
Triquetrum, the, 167. 
Troughton’s quadrants, 160. 
True anomaly, 99. 
Twilight, morning and evening, explanation of, 
127. 
Tycho de Brahe, planetary system of, 103; his 
mural quadrant, 159. 
Uranus, moons of, 117 ; observations of Madler 
on, 141. 
Variable stars, 96. 
Venus, apparent course of, 80; principal phases 
of a transit of, 111, 121; length of the day 
and nature of the seasons of, 147. 
Volumes of the planets, 105. 
Wheel clock, the, 169. 
Zodiac, the twelve constellations of the, 91. 
