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77 14 W.

4. 1872, June ist, in longitude 44° 40' E., observed meridian altitude sun's L.L. was 72° 14' 10", zenith North of sun, index correction + 3' 45', height of eye 22 feet: required the latitude.

5. In latitude 62° 39' N., the departure made good was 25'07: required the diff. long. by parallel sailing. 6. Required the course and distance from Cape Lopatka to Callao.

Latitude Cape Lopatka 50° 33' N. Longitude Cape Lopatka 156°46' E. Latitude Callao

4 S. Longitude Callao 7. 1872, May 4th: find the A.M. and P.m. tides at Aberdeen, Dunbar, and Wick.

7a. 1872, December roth: find the times of high water A.M. and P.m. in longitude 45° W., change tide 3h 12m.

76. 1869, December 13th: find the A.M. and P. M. tides at Fécamp (Admiralty Tide Tables).

8. 1872, August 1oth, at 7h iom A.m, apparent time at ship, latitude 55° 10' S., longitude 156° E., sun rose by compass E. 11° 20' S. (ship’s head due West, deviation 11° 30' W.): required the variation.

9. 1872, January 29th, P.M. at ship, latitude at noon 28° 45' N., observed altitudo sun's L.L. 17° 46' 30", index correction - 3' 25", height of eye 16 feet, time by a chronometer, January 28d 16h 31m 30s, which was slow im 3. for mean noon at Greenwich, January ist, and losing 993 daily, course since noon N.W. by W. (true), dist. 20 miles: required the longitude of ship at noon.

THE SAME, AS PROPOSED AT LIVERPOOL.

1872, January 29th, at about 4h im P.M. at ship, latitude at noon 28° 45' N., longitude account 171o E., observed altitude sun's L.L. 17° 46' 30", index correction - 325", height of eye 16 feet, time by chronometer 4" 31m 30%, slow im 38 on January ist, and losing 983 daily, course since noon N.W. by W. (true), distance 20 miles : required the longitude at the time of observation, and also at noon.

ADDITIONAL FOR FIRST MATE.

II.

10. 1872, June 15th, mean time at ship 7h 15m A.m., latitude 52° 25' N., longitude 2° 18' E., sun's bearing by compass S. 78° 56' E., observed altitude sun's v.L. 29° 56' 40", index correction + 34", height of eye 18 feet, variation by chart 21° W.: required the error of compass and deviation.

1872, November 29th, P.M. at ship, latitude account 6° 20' S., longitude 123° 25' E., observed altitude of sun's L.L. 72°, index correction + 4' 0", eye 19 feet, time by watch November 28d 22h 46m, which had been found to be ih 53m slow on apparent time at ship, the difference of longitude made to West was 12''3, after the error on apparent time was determined: required the latitude.

ADDITIONAL FOR MASTER ORDINARY. 1872, May 15th, the observed meridian altitude of the star Orionis 52° 20' 30", zenith North of star, index correction - 4' 10", height of eye 15 feet: required the latitude.

13. Work the day's work on page 260, using the table of deviations, page 138.

12.

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4. 1872, October ist, in longitude 84° 40' E., observed meridian altitude sun's u.L., bearing North, was 57° 20' 30", index correction — 3' 36", height of eye 17 feet: required the latitude.

5. A ship from latitudo 35° 30' S., longitude 27° 28' W., sailing due East (true) 301 miles : required the compass course steered, and what will be the longitude in, variation 14 point E., and deviation 8° 50' E. 6. Required the course and distance from A to B. Latitude A 10° 8' S.

Longitude A 175° 18' E.
Latitude B 23 12 N.

Longitude B 141 15 E.
Variation point West, and deviation 7° 15' W.
7. 1872, August ist: find the times of high water A.m. and P. M. at Leith Pier, Tay
Bar, Rye Bay, and Dunkerquc.

7a. 1872, May 3rd: find the times of high water A.M. and P.m. in longitude 40° W., chango tide 2b 30m.

76. 1869, August 20th: find the A.M. and P.M. tides at Sheerness (Admiralty Tide Tables).

8. 1872, May 11th, at gh P.M. apparent time at ship, latitude 38° 50'S., longitude 139° 25' E., sun setting by compass W.N.W., variation by chart 5° 8' E.: required the error of compass and deviation.

9. 1872, August 24th, A M. at ship, latitude at noon 37° 59' N., observed altitude of sun's L.L. 37° 13' 30", index correction + 2' 40", height of eye 18 feet, time by chronometer, August 244 6h 8m 139, which was 4m 65 slow on Greenwich mean noon, August 1st, and losing 1199 daily, course since obscrvation N.N.W, 22''4 (true) : required the longitude at noon.

THE SAME, AS PROPOSED AT LIVERPOOL:

10.

II.

1872, August 24th, at about 8h 40m A.M. at ship, latitude at noon 37° 59' N., longitude account 143° 45' W., observed altitude sun's L.L. 37° 13' 30", index correction + 2' 40", height of eye 18 feet, time by chronometer 6h 8m 13*, which was 4m 63 slow on Greenwich mean noon, August ist, and losing 1189 daily, course since observation N.N.W., 22:4 (true): required the longitude at noon.

ADDITIONAL FOR FIRST MATE. 1872, February 27th, mean time at ship 5' 25m P. M., latitude 37° 20' S., longitude 14° 10' W., sun's bearing by compass W. by N. 1 N., observed altitude sun's l'. I.. 14° 50' 30°, index correction — 1'3", height of eye 19 feet: required the variation.

1872, May 29th, A.M. at ship, latitude account oo 31' N., longitude 150° 40' W., observed altitude of sun's L.L., North of observer, was 67° 41', index correction ti', height of eye 20 fect, time by watch 294 3h 32mm, which had been found to be 4h 28m fast on apparent time at ship, the difference of longitude made to the East was 26''9 after the error on apparent time was determined: required the latitude,

ADDITIONAL FOR MASTER ORDINARY. 1872, June r’th, the longitude 98°W., observed meridian altitude of a Serpentis, zenith South of observer, was 29° 0' 40", index correction + 4' 20", height of eye 24 feet: required the latitude.

13. At the Cape of Good Hope the variation is about 289 W., if the sun at noon bear due North by compass, what is the deviation ?

12.

DESCRIPTION OF A SEXTANT.

A Sextant is constructed on the same principles as a quadrant, and furnishes the means of measuring the angle between two objects in whatever direction they may be placed, so that the angle does not exceed 140°

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B C is the arc or limb which is graduated from oo to about 140° (from C towards B), and each degree in the best instruments is again sub-divided into six equal parts of 1o' each, while the vernier g used in estimating the sub-divisions of the arc shows 10". The divisions are also continued a short distance on the other side of zero (o), towards C, forming what is termed the arc of excess, for the purpose of determining the index error in the manner that will be subsequently explained. The microscope M, and its reflector r secured at the point d by a movable arm d r to the index A E, may be adjusted to read off the divisions on the graduated limb and the vernier g. The index A E is secured to the arc B C by the intervention of a clamp screw & at its back, which must be loosened when the index has to be moved any considerable distance, and when the contact nearly has been made by hand, the screw is again to be fixed, and a tangent screw s' enables the index to be moved by a small quantity along the limb, so as to render the contact of the objects observed more perfect than could be effected by moving the index solely by the hand; the other extremity of the index has a silvered glass or reflector I fixed perpendicular to the plane of the instrument and directly over the centre; another glass b is fixed perpendicular to the plane of the instrument frame H, of which the lower half only is silvered and the upper transparent; the plane of this glass, usually termed the horizon-glass, is made parallel to the plane of the index giass I, when the vernier g is adjusted to zero on the divided arc B C, or if not so made, the want of parallelism constitutes what is termed the index error of the instrument. The telescope t is carried by a ring fastened to a stem E, which can be raised or lowered by a mill-headed screws' at the back of the frame, for the purpose of so placing the field of the telescope that it may be bisected by the line on the horizon-glass, separating the silvered from the unsilvered part, whereby the brightness of the reflected object and that seen by direct vision may be made equal, and the quality of the observations improved. It is usual to supply a direct and inverting telescope, of which the latter is to be preferred, as possessing greater magnifying power, and thus showing a better contact of the images of the objects. Two wires parallel to each other, and to the plane of the instrument, are placed in the inverting telescope, within which limit the observation should be made.

Dark glasses of different colours and shades are a necessary accompaniment to the sextant to enable the sun to be observed, and they are usually attached to a hinged joint as K. Four of these glasses or shades are placed at a, between the index and horizon-glasses, so as to admit of one or more of them being interposed between the index and horizon-glass. Three more such glasses, sometimes called back shades, are placed behind the horizon-glass at K, any one or more of which can also be turned down to moderate the intensity of the light before meeting the eye, when observing a bright object, such as the sun. There is also a dark glass, which can be placed at the eye-end t of the telescope, which method is preferable to the other, as no error in this is liable to be introduced in the passage of the rays from the index to the horizon-glass.*

With respect to the dark glasses, when it is possible (as in observing altitudes of the sun in the mercurial horizon, &c.) to make the observation with a single dark

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