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which aligns itself in a north-south direction) to construct their fortune
telling boards.
_______ someone noticed that the lodestones were better at
pointing out real directions, leading to the first compasses. They

designed the compass on a square slab which had markings for the
cardinal points and the constellations. The pointing needle was a
lodestone spoon-shaped device, with a handle that would always point

south. The first person recorded to have used the compass as a
navigational aid was Zheng He (1371-1435), from the Yunnan
province in China, who made seven ocean voyages between 1405 and
1433.

There are two main kinds of magnetic compass used in surveying
– the Surveyor's compass and the Prismatic compass. The
surveyor's compass is usually the larger and more_________, and is

generally used on a stand or tripod. The prismatic compass is often a
small instrument which is held in the hand for observing, and is
therefore employed for less accurate work.

This surveyor's compass consists of a long, thin, pointed needle of
magnetized steel with a small conical-shaped bearing of agate material
at the centre. The end of this needle which points north, the north end,

is differentiated from the other end, the south end, by a small metal
pin which passes horizontally through the needle near its north end.
The agate bearing works on a pointed pivot of hard steel carried at the
centre of the low cylindrical metal box (140mm in diameter).

__________ to the opposite ends of this box are two sighting vanes
with two slow motion screws and clamps which enable a definite line
of sight to be defined or laid out. _____________ can either be

screwed on to a tripod or remain hand-held for the purpose of
measuring magnetic bearings. The metal box carries inside it, three
graduated horizontal circles: top and lower circles 0-360 degrees, third
circle in quadrants 0-90 degrees, with the N and S directions identified

as zero points and the E and W directions are labelled as 90 degrees
each. The lower horizontal circle can read to 3 minutes directly on the
vernier. The azimuths are commonly measured on the top circle

clockwise from north through 360 degrees. A disc of glass, fitting on
top of the metal case, protects the needle and graduated circles.
In this instrument, the needle remains in a ________ (the position

of the magnetic south to north line), while the two upper graduated
circles, together with the line of sight, rotate about the vertical axis.

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