186

LATITUDE BY REDUCTION TO MERIDIAN.

Ex. 5. 1865, May 29th, P.M. at ship, lat. acct. 37° 15′ S., long. 107° W., obs. alt. sun's L.L. 30° 22′ 30′′ N., index corr. + 49′′, eye 22 feet, time by watch 29d 7h 9m 118, which had been found to be 6h 36m 568 fast on app. time at ship, diff. of long. made to West was 27' after the error on app. time at ship was determined.

Ex. 6. 1865, June 19th, A.M. at ship, lat. acct. 44° 24′ N., long. 14° 5′ W., obs. alt. sun's L.L. 68° 37′ 5′′ South of observer, eye 18 feet, time by watch 18d 20h 40m 40a, which was found to be 3h 2m 2 slow on app. time at ship, diff, of long, made to East was 32''5 after error on app. time at ship was determined.

Ex. 7. 1865, July 16th, P.M. at ship, lat. acct. 0° 38′ S., long. 2° E., obs. alt. sun's L.L. 67° 41′ (zen. S.), eye 15 feet, time by watch oh 11m 93, found fast on app. time at ship 563, diff. of long. made since 1 to East.

Ex. 8. 1865, August 30th, P.M. at ship, lat. acct. 41° 5' N., long. 139° 25′ E., obs. alt, sun's L.L. 57° 20' S., index corr. + 2′ 21′′, eye 14 feet, time by watch 29d 22h 22m 223, found to be 2h om 183 slow of app. time at ship, diff. of long. made to West was 34'.

Ex. 9. 1865, Sept. 9th, P.M. at ship, lat. acct. 9° 20′ S., long. 178° 30′ E., obs. alt. sun's L.L. 85° 19′ (zen. N.), eye 20 feet, time by watch 11h 59m 403, slow on app. time at ship 9m 218, diff, of long. made to East was 10.

Ex. 10. 1865, Oct. 11th, P.M. at ship, lat. acct. 45° 51′ N., long, 85° 3′ E., obs. alt. sun's L.L. 36° 38′ 15′′ S., index corr. 5′ 15′′, eye 16 feet, time by watch 10d 18h 50m 10s which was 5h 40m 12s slow on app. time, diff. of long 33′ West.

Ex. 11. 1865, Nov. 3rd, P.M. at ship, lat. acct. 32° S., long. 109° 39′ E., obs. alt. sun's L.L. 71° 50' N., index corr. + 32", eye 18 feet, time by watch 2d 22h 22m, which was found 2h slow, diff. of long. 28'7 West.

Ex. 12. 1865, Dec. 23rd, A.м, at ship, lat. acct. 47° 22′ S., long. 27° 3′ W., obs. alt. sun's L.L. 65° 10′ 15′′ N., index corr. +45", eye 12 feet, time by watch 22d 22h 59m 423, found to be 28m 40s slow, diff, of long, was 36' East.

Ex. 13. 1865, Jan. 5th, P.M. at ship, lat. acct. 8° 50' N., long. 130° 14′ W., obs. alt. sun's L.L. 58° 6′ 10′′ S., eye 21 feet, time by watch oh 2m 40s, found 13m 48s slow on app. time, diff. long, made since 16' East.

Ex. 14. 1865, April 28th, A.M. at ship, lat. acct. 18° 46' S., long. 34° 12′ W., obs. alt. sun's L.L. 56° 18′ (zen. S.), index corr.+1′5′′, eye 21 feet, time by watch 11h 40m 50a, found fast 2m 17s on app. time at ship, diff. long. made since 17 West.

Ex. 15. 1865, July 13th, A.M. at ship, lat. acct. 54° 35′ S., long. 152° 20' W., obs. alt. sun's L.L. 13° 17′ N., index corr. + 47", eye 12 feet, time by watch 13d 7h 54m 123, which had been found to be 8h 14m 17s fast on app. time at ship, diff. of long. made to West was 34' after error on app. time was determined.

obs.

Ex. 16. 1865, March 20th, A.M. at ship, lat. acct. 19° S., long. 33° 33′ W., alt. sun's L.L. 70° 21′ N., index corr. - 2′ 10′′, eye 16 feet, time by chron, 20d 7h 48m 179, found fast on app. time at ship 8h 6m 11s, diff. of long. made since 14 East,

Ex. 17. 1865, April 12th, A.M. at ship, lat. acct. 0°, long. 164° 12′ W., obs. alt. sun's L.L. 80° 36' N., index corr. - 5' 10', eye 21 feet, time by watch 12d oh om 2s, fast on app. time at ship 10m 51o, diff. of long. made to East was 7'.

Ex. 18. 1865, Sept. 16th, A.м. at ship, lat. acct. 42° 36′ S., long. 137° 10′ E., obs. alt. sun's L.L. 44° 6' N., index corr. + 2' 10', eye 19 feet, time by watch 16d 8h 41m 433, which had been found to be 9h 2m 478 fast of app. time at ship, the diff. of long. made to West was 14' after the error on app. time at ship was determined,

Ex. 19. 1865, March 16th, A.M. at ship, lat. acct. 37° 42′ N., long. 61° 40′ E., obs. alt. sun's L.L. 50° 0′ 30′′ S., index corr. + 34", eye 15 feet, time by watch 10h 53m 31", found slow on app. time at ship 1h 3m 228, diff. of long. made since 18' West.

Ex. 20. 1865, December 31st, A.M. at ship, lat. acct. 52° N., long. 12° 53′ W., obs. alt. sun's L.L. 14° 46′ S., eye 19 feet, time by watch oh 56m, which was fast on app. time at ship 1h 5m 20s, diff. of long. 21'4 West.

Ex. 21. 1865, March 5th, P.M. at ship, lat, acct. 33° 35′ N., long. 78° E., obs. alt. sun's L.L. 49° 53′ 15′′ S., index corr. 3' 15", eye 22 feet, time by watch 4a 19h 2m 12o, found to be 5h 17m 12s slow, diff. of long. was 10' East.

Ex. 22. 1865, September 22nd, A.M. at ship, lat. acct. 45° 45′ S., long. 111° 42′ W., obs. alt. sun's L.L. 43° 50' N., index corr. - 5′ 40′′, height of eye 18 feet, time by watch 23d 7h 41m 10s, found to be 8h 4m 10s fast, diff. of long, was 13''5 East.

Ex. 23. 1865, December 23rd, P.M. at ship, lat. acct. 42° 16′ N., long. 4° 39′ W., obs. alt. sun's U.L. 24° 14′ 10′′ S., eye 11 feet, time by watch oh 50m 583, fast on app. time at ship 19m 38s, diff. of long. 21'3 West.

ON FINDING THE LATITUDE BY A MERIDIAN ALTITUDE OF A FIXED STAR.

RULE LXI.

1o. Take from Nautical Almanac the star's declination.

2o.

directs.

To the observed altitude apply the index error, as the sign attached

3°. Subtract the dip answering to the height of eye (Table 5, Norie; Table 30, Raper).

4°. Subtract the refraction (Table 4, Norie; Table 31, Raper), and thus get the true altitude.

5°. Subtract the true altitude from 90°; the remainder is the zenith distance.

6. Mark the zenith distance N. or S., according as the observer is North or South of the star.

7. Underneath this last place the declination, and take their sum if they have the same names; but take their difference, if they have unlike names ; the result, in either case, will be the latitude.

The declination of a fixed star changes so slowly that it may be taken out of the Nautical Almanac by inspection, without any practical error resulting; a Greenwich date, therefore, is clearly unnecessary.

8°.

When the zenith distance and declination are of the same name, the latitude is of that name; when the zenith distance and declination are of different names, the latitude takes the name of the greater.

Date,

a Andromedæ.

The stars are inserted in the Nautical Almanac in the order of their Right Ascension, from oh to 24h; it will, therefore, very much facilitate the finding of the given star in the Nautical Almanac, to turn, in the first instance, to the three pages (324-326, Nautical Almanac, 1865) and thence obtain the star's Right Ascension, which find at the top of one of the pages following (327-385, Nautical Almanac, 1865), which will give the star, and the declination will be found opposite the day in the side column which is nearest the given day. The degrees (°) and minutes (') are placed at the top of the column (as annexed), and the seconds (") are ranged below, for the sake of economizing space in the second column below the name of the star. If the seconds exceed 60", only take the excess of 60" and increase the minutes () at the top by 1'. Thus, on January 21st, the declination of Andromeda is 28° 20′ 52′′ N., and on October 18th, the declination is 28° 21′ 11′′ N.,-70"7 being '11", which last added to 28° 20′, which stands at the head of the column, gives the declination.

R.A

Decl. N.

Oh 1m

28° 20'

Jan. 1

25$.50

54"-6

11

25135

53'5

21

25.21

52°2

31 25'09

50'7

&c.

Ex. 2.
1865, March 12th, long. 10° E.,
obs, mer, alt. of the star Pollux, bearing
North, was 71° 59′ 10′′, index corr. +
1'15", height of eye 18 feet: required the
latitude.

Observed altitude of star
Index correction

27

71° 59′ 10′′

+

1 15

Index corr. + 1' 15", Dip - 19", true alt. 71° 55′ 56′′, 16' 44" N.

-4′ 50′′,
Latitude 13° 29′ 10′′ N.

EXAMPLES FOR PRACTICE.

In each of the following examples it is required to find the latitude :

N.W.

W.S.W.

33

455555 ∞ 444 N M M Nonst∞06 +2 M M N N M N N M +333 +33 3 3 +444

2

N.W. by W.

S.W.

S.

W.

LEE

WAY.

REMARKS, &C.

A point, in lat. 37° 3′ N., long. 9° o' W., bearing by compass N.E. E., distance 15 miles,

S.W. by W.

9

W. S.

43

Correct the courses for variation and leeway, and find the course and distance from the given point, and the latitude and longitude in by inspection.

4. 1865, January 1st, in longitude 109° 41′ W., the observed meridian altitude of sun's L.L. was 59° 59′ 50′′, bearing South, index error +50", height of eye 15 feet: required the latitude.

5. In latitude 59° 58′ N., the departure made good was 124 miles: required the difference of longitude by parallel sailing.

6. Required the course and distance from A to Tynemouth Light, by Mercator's