1486
THE NEW ZEALAND GAZETTE.
[No. 43

11. Example.—Having taken the following compass bearings of a distant object, find the object’s magnetic bearing, and thence the deviations :—

Magnetic Bearing required.

12. With the deviation as above, construct a curve of deviations on a Napier’s diagram, and give the courses you would steer by the standard compass to make the following courses magnetic :—

Magnetic courses: S.S.W., W.N.W., N.N.E., E.S.E.

Compass courses required:

13. Supposing you have steered the following courses by the standard compass, find the magnetic courses made from the above curve of deviations :—

Compass courses: W.S.W., N.N.W., E.N.E., S.S.E.

Magnetic courses required:

14. You have taken the following bearings of two distant objects by your standard compass as above; with the ship’s head at W. ½ S., find the bearings, magnetic :—

Compass bearings: W. by S., and N. ¾ W.

Magnetic bearings required:

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

16. How often is it desirable to test the accuracy of your table of deviations?

17. What is meant by variation of the compass; what is it caused by; and where can you find the variation for any given position?

18. The earth being regarded as a magnet, which is usually termed the blue and which the red magnetic pole?

19. Which end of a magnet (or compass-needle) is usually termed the red or “marked” end, and which the blue?

20. What effect has the pole of one magnet of either name on the pole of another magnet?

21. What is meant by “transient induced magnetism”?

22. Which is the red and which is the blue pole of a mass of soft vertical iron, by induction, and what effect would the upper and lower ends of it have on the compass-needle (a) in the Northern Hemisphere, (b) in the Southern Hemisphere, (c) on the magnetic equator?

23. Describe what is usually termed the sub-permanent* magnetism of an iron ship, and state when and how it is acquired, and which is the red and which is the blue pole, and why it is called sub-permanent magnetism.

24. Describe the meaning of the expression “co-efficient A.”

25. Describe the meaning of the expression “co-efficient B,” its signs and effects.

26. Describe the meaning of the expression “co-efficient C,” its signs and effects.

27. Describe the meaning of the expression “co-efficient D,” its signs and effects.

28. Describe the meaning of the expression “co-efficient E,” its signs and effects.

29. Would you expect any change to be caused in the error of your compass by the ship heeling over either from the effect of the wind or the cargo, &c.?

30. The compasses of iron ships being more or less affected by what is termed the heeling error, on what courses is this error usually at its minimum, and, on what courses at its maximum?

31. Describe clearly the three principal causes of the heeling error on board ship.

32. State to which side of the ship in the majority of cases is the north point of the compass drawn when the ship heels over in the Northern Hemisphere.

33. Under what conditions (that is, as regards position of the ship whilst building, and the arrangement of iron in the ship) is the north point of the compass-needle usually drawn to windward or the high side of the ship in the Northern Hemisphere, and, if not allowed for, what effect has it on the assumed position of the ship when she is steering on northerly and on southerly courses in the Northern Hemisphere?

34. Under what conditions (as in Question 33) is the north point of the compass-needle usually drawn to leeward or the low side of the ship in the Northern Hemisphere, and, if not allowed for, what effect would it have on the assumed position of the ship when she is steering on northerly and on southerly courses in the Northern Hemisphere?

35. The effects being as you state, on what courses would you keep away and on what courses would you keep closer to the wind in the Northern Hemisphere in order to make good a given compass course (a) when the north point of compass is drawn to windward or the high side of ship, and (b) when drawn to leeward or the low side?

36. Does the same rule hold good in both hemispheres with regard to the heeling error?

37. State clearly how that part of the heeling error due to the permanent part of the magnetism of the ship varies as the ship changes her position on the globe, and give the reason for it.

38. State clearly how that part of the heeling error due to the induction in transverse iron (which was horizontal when ship was upright), and iron vertical to the ship’s deck, varies as the ship changes her position on the globe.

39. Your compass having a large error, show by “Beall’s compass-deviascope” how you would correct it by compensating-magnets and soft iron (as usually practised by compass-adjusters in the mercantile marine) in order to reduce the error within manageable limits. Show also how the heeling error can be compensated.

40. As the co-efficient B (capable of being corrected) usually consists of two parts, one due to the permanent magnetism of the ship, and the other to vertical induction in soft iron, how should each of the two parts, strictly speaking, be corrected when compensating the compass?

41. If the whole of co-efficient B be corrected by a permanent magnet, as is usually done, what is likely to ensue as the ship changes her magnetic latitude?

*The term “sub-permanent magnetism” in these questions is used in the original sense, as proposed by the late Sir G. B. Airy, to denote the character of the permanent magnetism of an iron ship as distinguished from the permanent magnetism of a magnetised steel bar. The terms “sub-permanent” and “permanent” throughout these questions may therefore be considered as synonymous.