38. When Arcturus in Bootes was on the meridian, Altair in the Eagle was rising; required the latitude.

39. The latitude of a place, day of the month, and two stars that have the same azimuth, being given, how do you find the hour of the night?

40. On the 20th of February, what is the hour at Edinburgh when Capella and the Pleiades have the same azimuth, and what is the azimuth?

41. The latitude of a place, the day of the month, and two stars that have the same altitude, being given, how do you find the hour of the night?

42. At what hour at Dublin, on the 15th of May, will Benetnach in the Great Bear's tail, and y, in the shoulder of Bootes, have each 56 degrees of altitude?

43. The altitudes of two stars having the same azimuth, and that azimuth being given, how do you find the place of observation?

44. The altitude of Vega in the Harp, was observed to be 700, and that of Ras Algethi in the head of Hercules, 39 degrees; their common azimuth at the same time was 60° from the south towards the west; required the latitude of the place of observation.

45. The hour of the day being given, how do you find on what day of the year any known star will pass the meridian of a given place?

46. On what day of the month, and in what month, does Aldebaran come to the meridian of Philadelphia, at 5 o'clock in the morning at London?

47. The altitudes of two known stars being given, how do you find the latitude of the place of observaLion?

48. In north latitude the altitude of Procyon was observed to be 50 degrees, and that of Betelgueze in Orion, at the same time, was 58 degrees; required the latitude of the place of observation.

49. The latitude of a place and day of the month being given, how do you find how long Venus rises before the sun when she is a morning star, and how long she sets after the sun when she is an evening star?

50. On the 1st of September, 1825, the longitude of Venus was 3 signs, 25° 59′, and latitude 1° 16′ south; was she a morning or an evening star? If a morning star, how long did she rise before the sun at London; if an evening star, how long did she shine after sun-set ?

BOOK.III.

OF THE SOLAR SYSTEM, AND THE FIRMAMENT OF THE FIXED STARS.

CHAPTER I.

Of the bodies which compose the solar system.

1. The SOLAR SYSTEM Consists of the Sun in the centre; and of eleven primary planets, which, taken in the order of their proximity to that luminary, are Mercury, Venus, the Earth, Mars 8, Juno, Vesta, Ceres, Pallas, Jupiter 4, Saturn, and Uranus or Herschel

These are called primary planets, because they perform revolutions round the sun in their respective periodic times. The four planets, Juno, Vesta, Ceres, and Pallas, are sometimes called minor planets or asteroids.

2. It also contains eighteen other small planets, that revolve round several of the primary ones, and on that account are called secondary planets or satellites; besides a considerable but indeterminate number of COMETS.

The Moon is therefore considered as one of these secondary planets, or satellites, because she performs her revolutions round the Earth; the rest are, the four satellites or moons of Jupiter, the seven satellites of Saturn, and six belonging to the planet Uranus or Herschel. All the planets, both primary and secondary, are opaque bodies, which borrow their light from the Sun.

The solar or planetary system, is usually confined to narrow bounds; the stars, on account of their immense distance, and the little relation they seem to bear to us, being accounted no part of it.

3. The primary planets all revolve eastward, or in the order of the signs of the zodiac, round the sun as a centre, in elliptic orbits, or paths which are nearly circular. All these orbits, ex cept that of the Earth, lie in planes different from that of the ecliptic, and the angle which the plane of any makes with that of the ecliptic, is called the inclination of that orbit.

4. Mercury, the nearest planet to the sun revolves round that luminary in about 88 days, at the mean distance of 37 millions of miles.

For the exact duration of the sidereal revolutions of the planet, the student is referred to the table towards the end of this chapter.

The period of time which a planet employs during its side*real revolution, or in passing from any fixed star till its returning to the same again, is the length of that planet's year.

5. Venus revolves round the sun in about 225 days, at the mean distance of 69 millions of miles. 6. The Earth revolves round the sun in about 365 days, at the mean distance of 95 millions of miles. 7. Mars completes his revolution in about 687 days, at the mean distance of 145 millions of miles. S. Vesta completes a revolution in about 1335 days, at the mean distance of 225 millions of miles. 9. Juno, in 1591 days, at the mean distance of 253 millions of miles.

10. Ceres, in 1681 days, at the mean distance of 262 millions of miles.

11. Pallas, in 1682 days, at the mean distance of 263 millions of miles.

12. Jupiter, in about 4333 days, at the mean distance of 494 millions of miles.

13. Saturn, in about 10,759 days, at the mean distance of 906 millions of miles,

14. Uranus or Herschel, in about 30,689 days, at the mean distance of 1822 millions of miles.

The two planets, Mercury and Venus, are called inferior planets, because their orbits are included in that of the Earth, and because they perform their revolutions in less than a year.

The eight planets, Mars, Juno, Vesta, Ceres, Pallas, Jupiter, Saturn, and Uranus, require a longer period than a year to complete their revolutions round the Sun; and as their orbits include that of the Earth, they are called superior planets.

15. The Moon, the Satellites of Jupiter, Saturn, and Uranus, describe orbits round their respective primaries, similar to those which the planets describe round the sun.

16. The motions of the Comets are very complicated; their orbits, instead of being nearly circular, like those of the planets, are very eccentric. Sometimes a comet approaches so near the sun as to be hid in his rays; at other times, it recedes from that luminary so far as to be carried beyond the planetary system, and does not return for several hundred years.

The comets are opaque bodies, which borrow their light from the sun; they are principally distinguished from the planets by their tails, or some hairy or nebulous appearance, and their always disappearing after having been visible only for a few months.

TABLE.

Of the sidereal revolutions of the primary planets.

Days. Years. Days. Hours. Min. Sec. 87.96926 0 87 23 15 44

Mercury

Ο 224 16 49 11

The year in this table contains only 365 days of mean

solar time.