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In the computation of the preceding eclipses of the sun and occultations, the ellipticity of the earth was assumed to be one three-hundredth, and the semidiameter of the sun was diminished 31" for irradiation, and that of the moon 2” for inflexion, according to the theory of Dusejour.

The elements are given in apparent time for the meridian of Greenwich, reckoned according to the manner of astronomers from noon to noon. When apparent is to be converted into mean time, the equation of time must be applied with the sign prefixed to it, but when mean time is to be reduced to apparent, the sign of the equation must be reversed.

No sign is prefixed the hourly motion of the moon in longitude, or of the sun in right ascension (AR), as they are always additive.

In the computation of an eclipse of the sun, or of an occultation, for any place, the latitude of the place and the moon's equatorial parallax must be reduced for the ellipticity of the earth, which is generally supposed to be one three-hundredth ; these reductions will be found in the 38th table of the “ New American Practical Navigator," or they may be computed by the following formulæ.

Let L be the latitude and R the reduction of the latitude, then log. cotang. (L-R)= 0,0029001 + log. cotang. L. The reduction of equatorial parallax, (57' for example,) may be found thus, 5.7'' – 5.7"' cos. 2 L.

ECLIPSES OF THE SATELLITES OF JUPITER IN 1830, Visible in the United States ; the phases of which are expressed in mean solar time for the meridian of Washington (5h. 7m. 428. west of Greenwich), reckoned, according to the manner of Astronomers, from

noon to noon.

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June

d. h. Jan. 15 17 49 47

17 16 59 41

31 16 5 21 Feb. in 17 58 51

17 15 52 15
18 16 40 40
23 ' 16 14 4
24 16 52 27

24 19 51 16 March 2 18 7 29

11 14 29 15
18 16 22 38
22 16 18 23
25 14 17 48

25 18 16 2 April 1 15 46 1

3 14 37 47 8 16 41 18 10 16 31 14 16 13 18 17 17 18 24 45 23 15 52 19 26 14 46 44

30 18 26 14 May 3 16 40 23

5 11 8 46
7 11 42 14

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13 2 30 14 12 33 21 14 15 41 12 18 12 50 43 19 14 56 20 21 16 31 41 25 15 24 28 26 16 50 15 28 11 18 48 31 12 40 46 31 14 59 3

4 13 12 52 11 . 15 7 3 12 9 48 52 13 9 35 35 17 9 16 19 11 39 54 19 12 22 43 20 11 29 56 26 12 27 27 26 14 56 38 26 15 39 51 27 13 24 24 3 16 26 33 3 17 30 42 6 12 1 43 7 9 27 7

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d. h.
Em. Sept. 15 7 14 11

16 11 20 8
20 12 23 47
22 9 941

29 11 5 10
Oct.

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4 5 51 18
8 7 29 28
11
8 23

1
15 9 24 53
Im.

18 11 4 56 Em.

19 4 30 11

19 7 52 54 Im.

22 11 20 15 Em.

24

5 49 7

26 30 57 Im.

29 6 55 51 Em.

31 7 44 26 Nov. 5 5 37 33

7 9 39 39

12 8 14 54 Im.

14 11 34 48
Em.

15 4 48 16
16 6 3 33
19 10 52 20
23 7 58 36

30 9 53 33
Dec.

4 32 59

2 4 22 18 Im.

7 5 26 42 Em.

9 6 17 9

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The eclipses before the opposition of Jupiter on the 5th of July, will take place on the west side of the planet, and afterwards on the east. The immersions only, of the 1st and 2d satellites will be visible before the opposi. tion, and the emersions only, after; but both the phenomena of the same eclipse, of the two outer satellites, can sometimes be seen.

The eclipses take place farthest from the body of Jupiter, when he is in quadrature, and nearest when in opposition or conjunction; but for some weeks before and after he is in the latter position, the eclipses cannot be observed; the planet and his satellites being lost in the rays of the Sun.

Eclipses of these satellites, particularly of the first and second, are very useful in determining, to a very considerable degree of accuracy, the longitude of any place; which, although not so exact as that obtained by an observed occultation of a star by the moon, is deduced without the long and fatiguing calculation necessary, in obtaining it by the latter method; they have likewise the additional advantage of being of very frequent occurrence.

To determine the time at which either of the preceding eclipse 3 will take place, on any other meridian than that of Washington, it is necessary, merely to add four minutes for every degree of longitude less than 76° 55' 30'', and subtract the same quartity for every degree greater. For Boston, add 23m. 258. ; for New York, ilm. 385. ' For Charleston, subtract 11m. 30s. ; for Cincinnati, 30m. 6s.; for New Orleans, 52m. 543.

Aug. 28.

Position and Magnitude of the Rings of Saturn, according to Bessel

and Struve, for every fortieth day in the year. Jan 1. - 7° 25' 14° 38' 46.00"

11.62'' Feb. 9. -7 33

15 57
46.96

12.91 March 21. -740

17 2
45.26

- 13.25
April 30.
-740

17 4
42.22

- 12.40 June 9. - 7 34

16 2
39.49

10.90 July 19.

7 22
14 12
37.90

9.30
12 2
37.67

7.86 Oct. 7.

6 48
10
38.87

6.76 Nov. 16. 6 36

8 44 41.32

6.27
Dec. 26.
6 34
8 40 44.34

6.68
p.
1.
a.

b. p: Angle between the semiconjugate axis of the ring ellipse, with the circle of declination; positive when east, negative when west.

l. Angle of elevation of the earth, above the plane of the ring, as seen from Saturn, positive when north, negative when south.

a. Semitransverse axis of the ring ellipse.

b. Semiconjugate axis; positive, when the northern surface of the rings is visible; negative, when the southern. It has lately been ascertained, that the planet is not exactly in the centre

of the rings.

The planet Mercury will be visible in the evening until the 11th of February, then in the morning to the 22d of April, then in the evening to the 15th of June, then in the morning to the 4th of August, then in the evening to the 12th of October, then in the morning to the 3d of December, then in the evening.

It is with difficulty that this planet can be seen in any other position, except when at or near its greatest elongation from the Sun, which this year happen January 27th (elongation 18° 24'), March 10th (27° 30'), May 21st (22° 32') July 8th (26° 29'), Sept. 17th (26° 29'), and Oct. 28th (18° 37'); but the following periods will be most favorable for observing it, this year, as during them it will not only be at its greatest distance from the Sun, but will be nearer the elevated pole, and consequently, will remain longer above the horizon. From Jan. 16th to Feb. 4th, in the evening after sunset, bearing W. 15° S. « May 1st “ June 4th, in the morning before sunrise, “ E. 23 N. Oct. 19th " Nov. 7th,

E. 6 S. The planet Venus will be visible in the evening to the 7th of March, then in the morning to the 20th of December, then in the evening; its greatest western elongation (45° 59') will take place on the 16th of May; but it will be the brightest, as evening star, on the 13th of January, and as morning star, on the 25th of April.

The planet Mars will be visible in the morning to the 19th of September, then in the evening to the end of the year.

The planet Vesta will be visible in the morning to the 8th of October, then in the evening.

The planet Pallas will be visible in the morning to the 27th of April, then in the evening:

The planet Juno will be visible in the morning to August 25th, then in the evening

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The planet Ceres will be visible in the morning till the 30th of April, then in the evening

The planet Jupiter will be visible in the morning till July 5th, then in the evening:

The planet Saturn will be visible in the morning till the 31 of February, then in the evening to the 14th of August, then in the morning to the end

The planet Uranus or Herschel will be visible in the evening till the 26th of January, then in the morning to August 1st, then in the evening to the end of the year.

The superior planets, or all but Mercury and Venus, will appear brightest when nearest to the earth, that is, when in opposition to the sun.

of the year.

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HEIGHT OF THE GREATEST OR SPRING TIDES IN 1830, Computed by the formula of La Place (Mécanique Céleste, vol. II. p. 289.) New or Full Height of New or Full

Height of Moon. the Tide. Moon.

the Tide. Full M. Jan. 8th, 10h. a. 0.88 Full M. July 5th, 9h. a. 0.85 New . 24 j1 0.99 New •

19 7

0.89 Full Feb.

2
0.88 Full Aug. 4

8

0.94 New! 22 11 1.11 News

18 7

0.89 Full March 9

0.88 Full Sept. 2

6

1.04 24 9 1.12 New

16 10

0,89 Full April 8 2 m. 0.86 Full Oct. 2 3 m.

1.14 22 6 1.08 New

16 3 a. 0.86 Full

7
0.83 Full

31 0

1.13 New o

22 2 m. 0.99 New Nov. 15 9 m. 0.83 Full June 6 9 0.81 Full

29 10 a. 1.05 20 10 0.94 New Dec. 15 3 m. 0.82

Full
29 9

0.98 The unit of aliitude, is the altitude of the tide which happens about a day and a half after the time of new or full moon; at the moment of new or full moon the sun and moon being at their mean distance from the earth, and in the plane of the equator.

The unit of altitude of any place, multiplied by the numbers in the preceding Table, will give the height of the tide at that place.

The unit of altitude at Boston, Salem, Marblehead, and Cape Ann, is

• May

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At New YORK, St. Augustine, Block Island, Elizabeth Town Point, Florida Keys, Hillsborough Inlet, Nantucket Shoal and Town, New Bedford, Rhode Island, and Sandy Hook, 5 feet.

At CHARLESTON, S. C., Monomoy Point, Port Hood, Prince Edward's Islands, St. Simon's Bar, and St. Simon's Sound, 6 feet. These, multiplied by the numbers in the preceding table, give the following, as the heights of the greatest tides, this year, in those places. Tide of Boston, N.York, Charleston, Tide of Boston, N. York, Charleston.

&c.
&c.
&c. &c.

&c. ft. in. ft. in. ft. in.

ft. in. ft. in. ft. in. Jan. 9 9 11 4 5 5 3

April 9 98 4 1 5 2 25 11 2 4 11 5 11

23 12 2 5 5 6 6 Feb. 8 9 11 4 5 5 3

May 8 94 4 2 4 11 23 12 6

6 8

23 11 2

4 11

5 11 March 10 9 11 4 5 5 3 June 7 9 1 4 1 4 10 25 12 7 7 6 9

21 10 7 4 8 5 8

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Tide of Boston, N. York, Charleston, Tide of Boston, N. York, Charleston,

&c.
&c.
&c. &c.

&c.
ft. in. ft. in. ft. in.

ft. in. ft. in. ft. in. July 6 97 4 3 5 1 Oct. 17 9 8 4 4 5 2 20 10 0

5 4 Nov. 1 12 9 5 8 6 10 Aug. 5 10 7

5 8

16. 9 4 4 *2 4 11 19 10 0

5 4 Dec. 1 11 10 5 3 6 4 Sept. 3 11 8

6 3

16 9 3 4 1 4 11 17 10 0

5 4

30 11

0 4 11 5 11 Oct. 12 10

5 8 6 11 It appears by the preceding Table, that the tides of February 23d, March 25th, October 3d, and November 1st, will be the greatest of all in 1830, but the positions of the Sun and Moon will not be so favorable this year as the last, for producing a great elevation of the sea; the height of the tides, however, depends so much on the strength and direction of the wind, that it not unfrequently happens that a tide, which would, independently of this, have been small, is higher than one in other respects much greater.

The following Table contains the unit of altitude of several ports and places on our coast, from the best authorities. The height of the enormous tides in the Bay of Fundy was ascertained from actual observation by a gentleman of Boston, in the summers of 1828 and 1829. Advocate Harbour (Bay of} Elizabeth Isles

9 feet. } 50 feet. Fundy)

Elizabeth Town Point

5 Andrews, St. 25 Florida Keys

5 Annapolis (Bay of Fundy) 35

Gay Head

7 Apple River

32
George's River

9 Augustine, St.

5
Georgetown Bar

4 Basin of Mines (Bay

of
Goldsborough

12
60
Fundy)

Green Islands

16 Bay, Bristed

Gut of Annapolis

28
Broad
9 Gut of Cansor

8
Casco
9 Halifax

8
Chignector (Forma part 360

Hillsborough Inlet
John's, St. (N. B.)

30
St. Mary's

16

St. (N. F.)
Vert
9 Kennebec

9
Beaver Harbour
7 Kennebunk

9 Bell Island Straits

30
Louisburg

51
Block Island
5 Machias

12 Cape Ann 11 Marblehead

11 Blomidom (Bay of Fu.) 55 Mary's, St., Bar

7
Chat

13
Monomoy Point

6
Cod

64 Moose River (Bay of Fundy) 35
Henlopen

5
Island

25
Henry.

Mount Desert

12 Look Out

9 Mouths of the Mississippi 13
May

6 Nantucket (Shoal and Town) 5
St. Mary
14 Nassau (N. P.)

7
Sable

9 New Bedford Split (Bay of Fundy). 49 Newburyport

10 CHARLESTON (S. C.) 6 New Haven Cumberland (Basin Fort),

NEW YORK

5 71 head of the Bay of Fundy Partridge Island (Bay of Fu.) 55 Digby (Bay of Fundy) 35 Passamaquoddy River 25 Eastport 25 Penobscot River

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