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

V111 ANALYSIS.
Art. Art.
To rectify the globe for the sun's Effect of a change in the place of the,lace............................. 73 earth's perihelion............. 104
Tfie latitude of the place being given, Causes of the inequality of the solar
to find the time of the sun's rising days............................ 105
and setting....................... 74 Explain the first cause, depending on
PROBL EMS ON THE CELESTIAL GLOBE.- the unequal velocities of the sun.. 10Q
To find the right ascension and decli- Explain the second cause, depending
nation....................... 75 on the obliquity of the ecliptic..106-108
To represent the appearance of the When does the sidereal day comheavens at any time...76 en.........e................ 109
To find the altitude and azimuth of a The Calendar.-Astronomical year destar....................... 77 fined............................ 110
To find the angular distance of two How the most ancient nations deterstars from each other............. 78 mined the number of days in the
To find the sua's meridian altitude, year.............................. 111
the latitude and day of the month Julius Cesar's reformation of the calbeing given...................... 79 endar explained. 111
Errors of this calendar............. 112
Chapter III.-PARALLAX - REFRACTION- Reformation by Pope Gregory....... 112
TWILIGHT. Rule for the Gregorian ealendar..... 112
Parallax defined-diurnal........... 80 New style, when adopted in England. 113
True place......................... 81 What nations still adhere to the old
Relation of parallax to the zenith dis- style............. 113
tance, and distance from the center What number of days is now allowed
of the earth..................... 82 between old and new style...... 114
To find the horizontal parallax from How the common year begins and
the parallax at any altitude....... 83 ends..................... 115
Amount of parallax in the zenith and How leap year begins and ends....... 115
in the horizon................... 83 Does the confusion of different calenEffect of parallax upon the altitude of dars affect astronomical observations 116
a body........................... 84
Mode of determining the horizontal Chapter V.-ASTRONOMICAL INSTRUMENTS
AND PROBLEMS-FIGURE AND DENSTrr
parallax of a body........... O 85 E EART
Amount of the sun's hor. par...... 86 OF THE EARTH.
Use of parallax..... 87 How the most ancient nations acquired
Refraction.-Its effect upon the alti- their knowledge of astronomy..... 117
tude of a body............. 88 Use of Instruments in the AlexanIts nature illustrated........... 88 drian School.................... 117
Its amount at different angles of ele- Ditto, by Tycho Brahe.............. 117
vation............................ 89 Ditto, by the Astronomers Royal.... 117
How the amount is ascertained.....90-91 Space occupied by 1" on the limb of
Sources of inaccuracy in estimating an instrument.................... 117
the refraction................... 92 Extent of actual divisions on the limb. 118
Effect of refraction upon the sun and Vernier defined..................... 118
moon when near the horizon...... 93 Its use illustrated.............. 119
Oval figure of these bodies explained. 94.Chief astronomical instruments enuApparent enlargement of the sun and merated.......................... 120
moon near the horizon......... 95 Observations taken on the meridian. 120
Twilight.-Its cause explained....... 96 Reasons of this..................... 120
Length of twilight in different lati- Transit Instrumen t defined.......... 121
tudes.............. 97 Ditto, described..... 121
How the atmosphere contributes to Method of placing it in the meridian. 122
diffuse the sun's light........... 98 Line of collimation defined......... 123
Chapter IV. —Tm E. T System of wires in the focus........ 128
Astronomical Clock-how regulated.. 124
Time defined..................... 99 What does it show.................. 124
What period is a sidereal day........ 100 How to test its accuracy............. 124
Uniformity of sidereal days......... 100 Rate and error...................... 124
Solar time, how reckoned........... 101 American method.................. 125
Why solar days are longer than side- Mural Circle-its object............ 126
real............................ 101 Describe it..............,... 126
Apparent time defined............., 102 How the different parts contribute to
Mean time...... 103 the object............ 126
An astronomical day..............., 103 Use of the Mural Circle for arcs of
Equation of time defined.......... 104 declination........... 127
When do apparent time and mean Altitude and AzimutA Instrument detime differ most........... 104 fined............................. 128
When do they come together......... 104 Its use............................ 128