Ex. 2. 1872, February 16th, at 4h 58m P.M. apparent time at ship, latitude 51° 9′ N., longitude 15 W., sun's magnetic amplitude W. 8° 26' N.: required the variation.

Ex. 3. 1872, April 13th, at 5h 47m 20s A.M., apparent time at ship, latitude 20° 2′ N., longitude 107° 56' E., sun's magnetic amplitude E. by N.

(A.M. and N. decl) True amplitude E. 9° 39' N.
(E. I point N.) Mag. amplitude E. 11 15 N. = E. by N.

Variation 36 E., the true amplitude being
to the right of magnetic.

The result as deduced above is generally called variation, but the effects of the iron in the ship modify the bearing by compass. Every error determined on board ship is compounded of variation proper and deviation and is the whole correction necessary to be applied to every bearing taken, and course steered, but will vary with the position of the ship's head and the heel of the ship. If the iron in the vessel exercises no influence on the compass, the result obtained is only variation, and ought to agree with that registered on the chart.

Ex. 4. 1872, June 10th, at 4h 45m P.M., apparent time at ship, latitude 36° 42' S., longitude 120' 30' E., magnetic amplitude N.W.

W.

Variation 7 20 W., because the true amplitude is to left of magnetic.

Ex. 5. 1872, July 31st, at 4h 26m A.M. apparent time at ship, latitude 46° 3' N., longitude 165° 58′ W., sun's magnetic amplitude E. 14° 4' N.

Ex. 6. 1872, Sept. 23rd, at 6h om A M., apparent time at ship, latitude 24' 40' S., longitude 179° 42′ E., sun's magnetic amplitude E. 10° 40' S.

Ex. 7. 1872, December 10th, at 8h 27m A.M., apparent time at ship, latitude 54° 35′ N., longitude 53° 15′ W., sun's magnetic amplitude S. by E.

Ship date, Dec.
Long. 53° 15' W.

9d 20h 27m

Decl. at noon, Dec. 10th 22° 59′ 5′′ S.

Green. date, Dec. or, Dec.

sine

9.828513

The decl. is taken out at once from the Nautical Almanac; it being noon there is no correction.

(A.M. and S. decl.) True amplitude E. 42° 22' S.

Mag. amplitude E. 78 45 S.

Variation 36 23 W., the true amplitude
being to the left of magnetic.

Ex. 8. 1872, December 20th, at 4h 31m P.M., apparent time at ship, latitude 41° 12' N., longitude 110° 45′ E., sun's setting amplitude S.W. by W.

Green. date, December 19d 21h 8m. Declination 23° 27′ S. sine

Latitude

41 12

9'599827

secant o123543

H. diff. noon, Dec. 20th
T. from noon, 2h 52m=

+1′′-18

2.87

826

944

236

3'3866

Ex. 9. 1872, November 15th, at 6h 45m P.M., apparent time at ship, latitude 31° 56' N., longitude 75° 30′ W., sun's setting amplitude W. 15° 40′ S. H. diff. noon, 15th +37"-82 T. from noon 11h 47m=

(P.M. and S. decl.) True amplitude W. 22 18 S.

Mag. amplitude W. 15 40 S.

Variation 6 38 W., the true amplitude
being to the left of the magnetic.

Ex. 10. 1872, July 20th, at 7h om P.M., apparent time at ship, latitude 34° 51′ S., longitude 172° 28′ E., sun's magnetic amplitude W. by N. N.

Ex. 11.

N.

Variation 8 32 E, the true amplitude
being to the right of the magnetic.

1872, March 24d 5h 58m P.M., apparent time at ship, latitude 22° 15′ S., longitude 179° 12′ W., sun's magnetic amplitude W. § S.

The Greenwich date is March 24d 17h 54m 48°. Then 24h - 17h 55m 6h 5m, or 6h nearly, the time from noon, March 25th.

The decl. noon, March 25th, is 2° 3′ 13′′ N., increasing. H. diff. 25th noon 58-82 X 61358802, or 5′ 59′′ subtractive, the decl. increasing will be less 6h 5m before noon than at noon, Red, decl. 1° 57′ 14′′ N.

Ex. 12. 1872, March 6d 5h 30m A.M., apparent time at ship, latitude 50° 50' N., longitude 47° 12′ E., sun's rising amplitude E. † S.

The Greenwich date is May 5d 14h 21m 125; time from nearest noon, May 6th, is 9h 39m, or 9h 65. Decl. page I, N. A., May 6th, noon, 16° 42′ 7′′ N. (incr.) H. diff. May 6th at noon, 41" 72 × 9h·65= 402" 5980, or corr. 6' 43". The decl. being increasing and required for 9h65 before noon, the corr. must evidently be subtracted to take the decl. back to Greenwich date, whence red. decl. is 16° 35′ 24′′ N.

9.655254

(A.M. and N. decl.) True amplitude E. 26° 53′ N.

Mag. amplitude E. 2 49 S.

Variation 29 42 W., the true amplitude
being to the left of the magnetic.

EXAMPLES FOR PRACTICE.

In each of the following examples the variation is required :—

CIVIL DATE.

APP. TIME.

O A.M.

51 22 S.

48

o E.

E.

2 P.M.

8.

July 14th,

6 50 58 A.M.

52 30 N.
28 59 S.

24 22 N.

21

4 S.

36 19 E.

57 30 W.

E.

42 44 S.
56 41 S.

175 15 W.

N. by W. W.
N.F.

N.W. by W.

E. by N. N.

E.

81 15 E.

E.

13.

Nov. 3rd,

Dec. 4th,

7 56 48 P M.

634 O P.M.

29 20 S.

49 59 S.

160 45 E.

15.

March 20th,

55 10 N.

68 45 E.

W. by S. & S.
N.W. W.

98 45 W.

ON FINDING THE TIME OF HIGH WATER.

FIRST METHOD-By Nautical Almanac.

In the Nautical Almanac the mean time of high water at London Bridge is given for every day of the year, on the assumption that the time of high water on the days of the full and change, or as it is termed, the ESTABLISHMENT OF THE PORT (see Nautical Almanac for 1872, page 519) is 2. The first high water which occurs after mean noon of each day is inserted in the first column, and the second in the second column. Where a line () is inserted, it indicates that there is only one high water on that day. Thus, on 1872, March 6th, there is only one high water: it occurs March 6th, at 11h 57m (P.M.); but the succeeding high tide does not take place until o1 34" after mean noon March 7th. The time given, it will be observed, is expressed in astronomical time. Again, on January 8th, 1872, there is only one high tide: it occurs at January 8 12h 18m astronomical time; e. 12h 18m past the noon of