An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

9X A.NA LYSIS.
Art. Art.
Its converse................... 173 Direction of this motion............ 136
Measure of velocity in an orbit.;.... 174 Time of revolution of the line of apModification for those nearly circular. 174 sides............................. 196
Centlrifugal force......... 175 Present longitude of the perihelion... 196
First law of central force in circular Cause of advance of apsides......... 196
orbit......................... 176 Anomaly defined................... 197
Second ditto....................... 177 Anomalistic year, its length...... 197
Law of gravity in an elliptical orbit.. 178 Slow change in duration of the seasons. 198
Proof............................. 179 MEAN AND TRUE PLACES OF THE SUN.. 199
Same law for different orbits-proof.. 181 Mean Motion defined.............. 199
Bodies on the earth compared with Illustrated by surveying a field.... 199
the moon..................... 182 Mean and true longitude'distinuished 199
-Samle law explains disturbances...... 182 -Equations defined........ 200
Gravity as quantity of matter........ 182 Their object................... 200
Projectiles...................... 183 Mean and Trule Anomaly defined 200
Why parabola, not ellipse........... 183 Equation of the center.............. 200
Time of complete revolution of a pro- Explain from the figure.......... 200
Iectile........................... 183GEOGRADifferent forms of projectile paths... 184
Place of perigee and ap)oee.. 184
- — n - -~- r~- - LUTIONS.
Annual and diurnal rotation by one
impulse.......................... 185 Distance of the moon fiom the earth. 201
Effect of impulse on the system..... 186 Her mean horizontal parallax........ 201
Two bodies supposed............... 186 Her diameter....................... 201
Motion of center............. 186 Volunle, density, and mass.......... 201
Motion of each body................ 186 Shines by reflected light............ 202
Epicycloids, two forms.............. 186 Appearance in the telescope.......... 202
Where retrograde,nmotion......... 186 Terminator defined................. 203
How center can be kept at rest... 186 Its appearance...................... 203
Why planet returns from aphelion... 187 Proofs of mountains and valleys......203
Why it departs from perihelion..... 187 Form of the valleys................ 204
Chance inl centrifugal force, compared Ring-mountains-bulwark plains.... 204
withl that in centripetal........... 187 Lava-lines seen at full moon......... 205
Chapter IV. —PRECESSION OF THE EIUI- Water, clouds, vegetation. 205
NRoXES-NUTATION-AB HRRATION-MEAN Explain the lethod of estimating the
AND TaRUxE PlLACES OF THE SUN. height of lunar mountains......... 206
Has the moon an atmosp]here....... 209
Precession of the equinoxes defined.. 188 Improbability of identifying artificial
Why so called.. 188 structures in the moon.... 210
Amnount of precession annually... 189 PHASES OF THE MOON, their cause.... 211
Revolution of the equinoxes..... 1... 1'89 Successive appearances of the moon
Revolution of the pole of the equator fi'om one new moon to another.... 211
around the pole of the ecliptic..... 190 Syzygies defined.................. 211
Changes among the stars caused by Explain the phases of the moon from
precession.................... 190 figure 46......................... 212
The presentpole-star not always such. 190 REVOLUTIONS OF THE MOON. Period
What will be the pole-star 13,000 years of her revolutions about the earth.. 213
hence?........................... 190 Her apparent orbit a great circle..... 213
Cause of the precession of the equi- A sidereal month defined....... 213
noxes.................1..... 191 A synodical do............. 213
Explatin how the cause operates..... 191 Length of each..................... 213
Proportionate effect of the sun and Why the synodical is longer........ 213
1mXoon in producing precession..... 192 How each is obtained. 213
The:law of' compounud rotations...... 192 Inclination of the lunar orbit........ 214
Tropical year defined............... 193 Nodes defined....................... 214
H-ow,nluchl shorter than the sidereal Why the moon sometimes runs high
year.............................193 and sometimes low............... 215
Use of.the precession of the equinoxes Harvest moon defined.............. 216
in chronology.................... 193 Ditto explained..... 216
NUn1AxION, defined.................. 194 Explain why the moon is nearer to us
Explain its operation............... 194 when on the meridian than when
Caullse of notation................. 194 near the horizon............. 217
ABERRATION, defined............ 195 Time of the moon's revolution on its
Illulstrated by a diagram............. 195 axis 218
Amnount of aberration................ 195 How known........................ 218
Effebct on the places of the stars...... 195 Librations explained............... 219
MOTION OF THE ArsDEs - the fact Diurnal libration.... 219
stated.......................... 196 Length of the lunar days........... 220