9. How are the eclipses of the sun and moon produced? Illustrate
   your answer by diagrams.

10. Account for the formation of a large number of images by two
    parallel mirrors. Illustrate your answer by a carefully drawn
    diagram.

11. Draw a diagram which will show the paths of rays of light through
    a telescope. How may the magnifying power by obtained?

12. Explain why the note of a siren seems different in pitch when
    a steamer is approaching and when it is receding from you.

NAVIGATION.

Paper 3 (3 hours).

1. What are the general principles underlying the construction of
   Special Tables for finding Position Lines? Explain how these
   principles are applied in particular to any such tables that
   you are familiar with.

2. Explain, with sketches if necessary, how you would know whether
   the failure of three bearings to intersect at a common point
   is due to an error common to all three bearings or to errors
   in the individual bearings, and say also what position you would
   consider to be the position of the ship on the chart, having proved
   the failure to be due to the second reason.

3. Explain the construction and use of a vernier, taking as an example
   the sextant, the arc of which is divided to $10'$, the vernier affording
   a degree of accuracy of $10''$.

4. Describe in detail the principle of a Rotating Wireless Beacon,
   and explain in detail how such a beacon can be used to facilitate
   coastal navigation.

5. Calculate the height of the tide off Dover at 04 hrs. G.M.T. on 10th
   December, 1929, by means of the Harmonic Tidal Constants.

6. Explain the course and speed errors of the Gyro compass. Find
   the error on such a compass in Lat. $50^{\circ} \mathrm{N}$. , ship steaming
   12 knots, course $320^{\circ}$.

CHART WORK.

Paper 4 (2 hours).

1. Discuss in detail the advantages and disadvantages of the position
   line by horizontal angle when used with another such line
   to determine the ship's position.

2. Draw sketches and describe in detail the use which may be made of
   one or more fixed objects on shore to ensure the safety of the
   ship when in the vicinity of hidden dangers.

3. How would you proceed to find the distance off a known object
   by vertical angle when the height of the object is known but its
   base is beyond the horizon?

4. Describe briefly, the usual method employed in reproducing and
   printing Admiralty Charts.

CHART CONSTRUCTION AND MARINE SURVEYING.

Paper 5 (3 hours).

1. Construct a plan to Natural Scale $\frac{1}{20800}$ between the limits
   $52^{\circ} 02 ' 30 ''$ and $52^{\circ} 06 '$ North Lat. and $7^{\circ} 31 '$ and $7^{\circ} 37 '$ West
   Long., and give a scale of Lat. and Dist. but no compass.

2. On the plan so constructed insert the following positions :—
   Wyse Pt. F.S. Lat. $52^{\circ} 05' \mathrm{~N}$. , Long. $7^{\circ} 34' 12'' \mathrm{W}$.
   Ballinacourty Pt. F.S. Lat. $52^{\circ} 4' 40'' \mathrm{~N}$. , Long. $7^{\circ} 33' 10'' \mathrm{~W}$.
   Helvich Harbour Lt. Ho. Lat. $52^{\circ} 3' 18'' \mathrm{~N}$. , Long.
   $7^{\circ} 32' 42'' \mathrm{~W}$.
   Two sounding boats A and B are in such positions that from
   A the observed angles were Wyse $50^{\circ} 30'$, Ballinacourty
   $84^{\circ} 40'$, Helvich, and from B the observed angles were Wyse
   $33^{\circ} 15'$, Ballinacourty $117^{\circ} 40'$, Helvich.
   Find the distances of each boat from Ballinacourty and
   Helvich respectively.

3. Write a brief description of the use of the Tide Pole to reduce tidal
   sounding to Chart Datum.