8. On what days do the same stars come to the meridian at 4 o'clock in the morning?

9. On January 1st, when it is half past eight in the evening at London, what are the altitude and azimuth of the following stars:-Algol; Pleiades; Menkar; Aldebaran ; Sirius; Procyon; Taurus, &; Capella; Leo, y; Cassiopeia, a; Cygnus, ; Vega; and Draco, «?

10. What are the altitude and azimuth of the following stars at London on May 1st, when it is 10 o'clock in the evening:-Cygnus, ; Corvus, ; Regulus; Cancer, «; Procyon; Dubhe; Perseus, «; and Capella?

11. On October 6th, the azimuth of Menkar, at Newcastle, was S. 52 E.; required the hour and the altitude.

12. At London, on December 21st, the azimuth of Cor Hydra was S. 14 W.; required the hour and the altitude.

13. At the Cape of Good Hope, on June 21st, the azimuth of Spica Virginis was N. 89 W.; required the hour and the altitude.

14. On August 9th, the altitude of Phoenix, «, at Jerusalem, was 14o; required the hour and the azimuth.

15. At Quito, on March 22d, the altitude of Canopus (Argo, a) was 21°; what was the hour?

16. What was the hour at London, on September 1st, when the altitude of Arided was 80°?

17. The azimuth of the brightest of the Pleiades, at Newcastle, was S. 88 E., when it was 10 in the evening; what was the day of the month, and what was the altitude of the star?

18. At Boston, in America, the azimuth of Rigel was S. E. by E. 7° E., when it was 8 hrs. 1 min. p. m.; required the day of the month.

P2

19. What time does Dubhe set at Newcastle on February 28th?

20. When it was 5 in the morning at Rome, the azimuth of Capella was N. 60 W.; what was the day of the month?

21. What is the time of the rising, setting, and culminating of Castor; Sirius; Corona Borealis, «; Arcturus; and Procyon; at London, on January 31st?

22. How long is Sirius above the horizon at Petersburgh?

23. What time does Achernar rise at York on September 2d?

24. What is the time of the rising, setting, and culminating of Algenib, Menkar, Vega, and Cor Hydra, at St. Helena, on October 6th?

25. What stars of the first and second magnitudes are above the horizon at London, on January 1st, at 9 o'clock in the evening?

26. Required the situation of the stars at York, on May 1st, when it is midnight.

27. What constellations never set at Rome? What constellations never rise there?

28. What stars never rise at the north pole? What stars never set there?

29. Are there any stars which never appear above the horizon at the equator?

30. Where must I go never to see Menkar?

31. Where must I go never to lose sight of Aldebaran ?

SECTION II.

OF THE SUN.

The sun is the centre of the solar system, all the planets moving round it at different distances, and in different periods its figure is nearly globular, and its diameter is almost equal to 111 times that of the earth, being about 883,217 miles; hence its surface is 12,300 times, and its bulk, or solid content, 1,380,000 times that of the earth: but the density of the matter of which it is composed is known to be four times less than the density of our globe. It is the attraction of the sun that retains the planets in their orbits, and to him they are indebted for light, heat, and motion. The sun is not absolutely at rest, but is found, by the spots on its surface, to turn round on its axis from west to east in about 25 days. The mean distance of the sun from the earth is 95,000,000 miles.

"The sun agrees with the fixed stars in the property of emitting light continually; and it is not improbable that they have many other properties in common. The sun is therefore considered as a fixed star comparatively near us, and the stars as suns at immense distances from us."

From being the source of light and heat, the sun was long supposed to be a body of fire: but Dr. Herschel, in two papers lately published in the Philosophical Transactions, supposes that the body of the sun is an opaque habitable planet, surrounded by a luminous atmosphere, which, being at times intercepted and broken, gives us a view of the sun's body itself, viz. the spots upon its surface. The sun's atmosphere, he thinks, is nearly 2000 miles in height; and he supposes that the density of the luminous solar

clouds needs not be much more than that of our aurora borealis, to produce that degree of light and heat which we receive from him.

If this hypothesis be admitted, the sun, then, is similar to the other globes in the solar system, with regard to its solidity, its atmosphere, its surface, diversified with mountains and valleys, the rotation on its axis,—and the fall of heavy bodies on its surface. It therefore appears to be a very eminent, large, and lucid planet, probably inhabited, disseminating light and heat to all the bodies with which it is connected.

The annual revolution of the earth produces the apparent motion of the sun among the stars in the ecliptic, by which he describes his annual path. This produces a daily change in right ascension and declination. The sun's amplitude and azimuth vary, both with the day of the month and the latitude of the place. The amplitude is always of the same name with the declination: the greatest amplitude north is, when the sun is in the north tropic; and south, when he is in the south tropic. Places that have the greatest latitude (not greater than 6610) have the greatest variation of amplitude; places at the equator have the least variation.

As all the problems relating to the sun may be performed on either globe, those that are given here must be considered as only supplemental to the problems relating to the sun given in Part II. Most of them are similar to the problems relating to the stars given in the last section; an enumeration of them here is, therefore, not necessary.

PROBLEM XIV.

To find the sun's right ascension and declination for any

day.

Bring the sun's place to the brass meridian; then the degree over it shows the declination, and the degree of the equator under the meridian shows the right ascension.

This is the same as Problem I. Part III.

The sun's declination and right ascension may be found in Tables II. and III. or in White's Ephemeris, for any day of the year.

To find the sun's oblique ascension, ascensional difference, eastern amplitude, and time of rising, on any given day, at any given place.

1. Elevate the globe for the latitude, bring the sun's place to the meridian, and set the index to 12.

2. Bring the sun's place to the eastern side of the horizon, and the degree of the equinoctial now at the horizon is the sun's oblique ascension.

3. The right ascension being found by the last problem,