페이지 이미지
PDF
ePub

ERRATA

Page 8.–First line after the diagram should read “CD is

a part of the earth's path.” 100.-Question 3, first line of answer, for “ Take a

spar topmast” read “ Take a spare topmast.” 115.– Question 3, the third line of the answer, for

excepted" read “expected.”

REED'S SEAMANSHIP.

FOR SECOND MATES.

ADJUSTMENT OF THE SEXTANT.

The applicant will answer in writing, on a sheet of paper which will be given to him by the Examiner, all the following questions, numbering his answers with the numbers corresponding to the questions : 1. What is the first adjustment of the sextant ?

The index glass must be perpendicular to the plane of the sextant. 2. How do you make that adjustment ?

Place the index near the middle of the arc, and look into the index glass, so that you can see both the arc and its reflection ; if they be in one line the glass is perpendicular; but if not in one line, they are brought so by gently moving the screws in the frame upon which the glass stands, slackening the inner ones and tightening the outer one, or the reverse, as is necessary. 3. What is the second adjustment ?

The horizon glass must be perpendicular to the plane of the sextant. 4. Describe how you make that adjustment.

Place the index of the vernier at 0 on the arc. Hold the instrument obliquely with its face upwards, and look at the horizon ; if the reflected part and the direct portion of the horizon are in one line, this adjustment is perfect; but if not, they must be brought in one line by gently moving a screw at the back of the glass. 5. What is the third adjustment ?

The index and horizon glasses must be parallel when the index is at 0. 6. How would you make the third adjustment ?

Place the index at 0, and, holding the instrument vertically, look at the horizon ; if the reflected and direct

parts are in one line, this adjustment is perfect ; but if they are not in one line, move a screw at the back of the horizon glass until they are. 7. In the absence of a screw how would you proceed ?

I would find the index error. 8. How would you find the index error by the horizon ?

Put the sextant at 0; hold it vertically, and looking at the horizon, I would move the tangent screw until the horizon in both parts of the horizon glass forms one line ; the reading is the index error. 9. How is it to be applied ?

To be added when the reading is off the arc, and to be subtracted when the reading is on the arc.

10. Place the index at error of minutes to be added, clamp it, and leave it.

NOTE.—The Examiner will see that it is correct. 11. The Examiner will then place the zero of the vernier on the arc, not near any of the marked divisions, and the candidate will read it.

Note.--In'all cases the applicant will name or otherwise point out the screws used in the various adjustments.

The above completes the examination of Second and Only Mates.

In addition to the above, First Mates and Masters will be required to state in writing :12. How do you find the index error by the sun ?

I would clamp the index at about 30' on the arc, and looking at the sun, two suns will be seen, bring their upper and lower limbs in exact contact by the tangent screw, read it, and mark down as on ; then clamp the index at about 30' off the arc, bring the lower and upper limbs in contact as before, read it, and mark down as off. Half the difference of these two readings will be the index error. 13. How is the same applied ?

It is to be added when the greater reading is off the arc, and subtracted when the greater reading is on the arc.

14. What proof have you that these measurements or angles have been taken with tolerable accuracy ?

I would add the two readings together, and divide the sum by 4; if the measurements are correct, the result should be nearly equal to the sun's semi-diameter for that day, as given in the Nautical Almanac; if they do not so agree, I would repeat my observations until they do.

GEOGRAPHICAL AND ASTRONOMICAL

DEFINITIONS.

FIRST EXAMINATION ONLY. The applicant is to write a short definition against so many of the following terms as may be marked with a cross by the Examiner. The Examiner will not mark less than 10. The writing should be clear, and the spelling should not be disregarded.

Note.—T'hose candidates who have already passed the Board will not be required to do the following 45 questions. 1. The Equator.

A great circle on the Earth, at equal distances from both Poles. 2. The Poles.

The ends of the axis of the Earth. The North end is called the North Pole, and the South end the South Pole. 3. A Meridian.

A great circle on the Earth perpendicular to the Equator, and passing through both Poles. 4. The Ecliptic.

The apparent path of the sun through the heavens in a year. It is the real path of the Earth. 5. The Tropics.

Are two lesser circles parallel to the Equator, and 23° 28' each side of it. The one to the North of the Equator is called the Tropic of Cancer, the one to the South the Tropic of Capricorn. 6. Latitude.

The distance any place is North or South of the Equator, measured on a Meridian. 7. Parallels of Latitude.

Lesser circles parallel to the Equator. Every place on the same parallel has the same Latitude.

8. Longitude.

The distance any place is East or West of the first Meridian, measured on the Equator.

[graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][ocr errors][ocr errors][subsumed][merged small]

a part of the earth's path through the

heavens, and A B the axis of the earth. Then E Q is the Equator ; N and S the North and South Poles ; NMS, NGS, NHS, NPL S, &c. are Meridians ; t R is the Ecliptic; TR is the Tropic of Cancer, and t r the Tropic of Capricorn.

Again, let P be the position of any place on the earth :

Then, P L is its Latitude; and if Ñ GS be supposed to be the Meridian that passes through Greenwich Observatory, then N G S is called the First Meridian, and G L is the. Longitude of P.

XY, TR, and tr, are Parallels of Latitude. The point in the heavens directly above Z is called the Zenith,

that below F the Nadir.

« 이전계속 »