JUNE 7.] THE NEW ZEALAND GAZETTE. 1491

3. What do you mean by deviation of the compass, and how is it caused?

4. Having determined the deviation, how do you know when it is easterly, and when westerly?

5. How could you find the deviation of your compass when in port, or when sailing along a coast?

6. Name some suitable objects by which you could readily obtain the deviation of your compass when sailing along the coasts of the channel you have been accustomed to see?

7. The bearing of two objects when in a line with each other was found on the chart to be magnetic, but when brought in a line on board they bore by your compass; required the deviation of your compass for the direction of the ship’s head at the time?

8. What means are there for checking the deviation of your compass by night?

9. Do you expect the deviation to change? If so, state under what circumstances.

10. What is meant by the variation of the compass, and what is the cause of it?

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APPENDIX M.

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COMPASS-ADJUSTMENT.

It is of the utmost importance that masters of ships should thoroughly understand the tentative method of compass-adjustment as generally practised in merchant ships, and Examiners are therefore directed to fully satisfy themselves that all candidates for masters’ certificates have this particular knowledge. It should be tested in connection with the Forms Exn. 7 and 7a, with the aid of Captain Beall’s deviascope, and candidates will be required to prove (1) their knowledge of the laws of deviation and the tentative methods of compass-adjustment; (2) that they understand the practical application of the answers given by them to any of the other questions on Forms Exn. 7 and 7a that the Examiner may ask.

A concise statement of the present method of tentative compass-adjustment is appended for the use of Examiners. It is, however, distinctly to be understood that the Marine Department is not in any way advocating the correction of that part of co-efficient B which arises from vertical induction in soft iron by a permanent magnet instead of by a soft-iron bar. The Department has no authority to interfere with the methods in use amongst compass-adjusters for the adjustment of compasses in iron ships, but the Examiners must satisfy themselves that masters are acquainted with the ordinary method as at present practised.

The Tentative Method of Compass-adjustment as generally practised by Compass-adjusters in Ships of the Mercantile Marine.

Before describing the practice, it will be as well to briefly state the co-efficients used to express the different magnetic forces:—

Co-efficient A represents a constant quantity.

,, B ,, semicircular deviation due to fore-and-aft magnetic forces.

,, C ,, semicircular deviation due to transverse magnetic forces.

Co-efficient D represents quadrantal deviation due to horizontal induction in soft iron.

,, E ,, quadrantal deviation due to horizontal induction in soft iron unsymmetrically distributed.

Signs and Effects of Co-efficients A, B, C, D, and E.

Co-efficient A represents a constant deviation of the same nature and amount on all points of the compass; + A signifying easterly, and — A westerly, deviation.

Co-efficient + B represents an attraction towards the ship’s head, and causes easterly deviations with the ship’s head in the eastern semicircle of the compass, and westerly deviations in the western semicircle, attaining a maximum value on the east and west points, decreasing to zero on north and south points, by compass.

Co-efficient — B represents an attraction towards the ship’s stern, and causes easterly deviations with ship’s head in the western semicircle, and westerly deviations with the ship’s head in the eastern semicircle, with a maximum value on the east and west points, decreasing to zero on the north and south points, by compass.

Co-efficient + C represents an attraction towards the starboard side of the ship, and causes easterly deviations with ship’s head in the northern semicircle, and westerly deviations in the southern semicircle, attaining a maximum value on the north and south points, decreasing to zero on the east and west points, by compass.

Co-efficient — C represents an attraction towards the port side of the ship, and causes westerly deviations with ship’s head in the northern semicircle, and easterly in the southern semicircle, attaining a maximum value on the north and south points, decreasing to zero on the east and west points, by compass.

Co-efficient + D gives easterly deviations with ship’s head between N. and E., and S. and W.; and westerly deviations between S. and E., and N. and W.

Co-efficient — D gives results exactly the reverse to + D.

NOTE.—Both + D and — D have a maximum value on the four quadrantal points, and become zero on the cardinal points, by compass.

Co-efficient + E gives easterly deviations with ship’s head between N.E. and N.W., and S.E. and S.W.; and westerly deviations between N.E. and S.E., and N.W. and S.W.

Co-efficient — E gives results exactly the reverse to + E.

NOTE.—Both + E and — E have a maximum value on the cardinal points, and become zero on the four quadrantal points, but are usually very small in amount in compasses placed in the middle line of the ship.

Heeling Error.—The heeling error arises partly from vertical induction in transverse iron, and iron vertical to the ship’s deck, and partly from the vertical component of the sub-permanent magnetism of the ship. In the Northern Hemisphere in the majority of cases the north point of the compass-needle is drawn to windward or the high side of the ship, with, as a rule, a maximum heeling error on north and south points, and zero on east and west points, by compass. If the compass is not properly placed in the ship there may be a sensible heeling deviation on east and west courses.