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Astrolabe

The astrolabe of Hipparchus is considered to be one of the best known of

the measuring instruments. It was developed sometime in 140 B.C., and further

improved by Ptolemy. The instrument had a metal circle with a pointer hinged at

its center and held by a ring at the top ,and a cross staff, a wooden rod about 1.25

meters long with an adjustable cross arm at right angles to it. The known length of

the arms of the cross staff allow distances and angels to be determined by

proportion. It was originally designed for determining the altitude of stars.

How to use Astrolabe (Measuring the

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Altitude of Trees and Buildings)To become familiar with how an astrolabe

works, practice measuring the altitude (angularheight) of trees or buildings. To make a propermeasurement, look at the top of the object

through the straw.Have someone read the altitude in degrees

from the side of the astrolabe. The point wherethe string crosses the scale is the proper

measurement.Practice using your astrolabe by measuring andrecording another tree or building of a differentheight.

Telescope

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The invention of the telescope in 1607 is accredited to Lippershey. In 1609,

Galileo constructed a refracting telescope for astronomical observation. However,

it was only when cross hairs for fixing the line of sight were introduced, that the

telescope was fixed in early surveying instrument.

Transit

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The invention is credited to Young and Draper who worked independently

from each other sometime in 1850. Both men were able to put together in one

instrument the essential parts what has long been known as the universal

surveying instrument.

Semicircumferentor

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An early surveying instrument which was used to measure and lay off

angles, and establish lines of sight by employing sights

Plane Table

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One of the oldest types of surveying instruments used in field mapping. It

consists of aboard attached to a tripod in such a way that it can be levelled or

rotated to any desired direction

Dioptra

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The dioptra, which was perfected by Heron of Alexadria, was used in

leveling and formeasuring horizontal and vertical angles. It consists essential of a

copper tube supported ona standard and could be rotated in either a horizontal

or vertical plane. For measuringhorizontal angles, a flat circular disc with

graduations in degrees is used. An arm containingsighting apertures at either end

could be rotated to any desired position on the disc.

Roman Groma

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The Roman surveyors used the groma instrument for aligning or sighting as an

points. It consisted basically of cross arms fixed at right angles and pivoted eccentrically upon

a vertical staff. Plumb lines were suspended from the ends of the arms. BY employing the

groma two lines at right angles to each other could be established on the ground where it is set up.

Libella

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The Assyrians and Egyptians are believed to be the first users of libella. The

instrumenthad an A-frame with a plumb line suspended from its apex and was

used to determine the horizontal. Archaeologist are of the belief that the

horizontal foundations of the great pyramids of Egypt were probably defined by

this device.

Vernier

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The vernier is a short auxiliary scale placed alongside the graduated scale of

an instrument,by means of which fractional parts of the smallest or least division

of the main scale can be determined precisely without having to interpolate. It

was invented in 1631 by a Frenchmanname Pieere Vernier. Surveying instruments

employ either a direct or retrograde.

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Diopter

An intrument developed by the Greeks sometime in 130 B.C., and known to

be their mostfamous surveying instrument. The diopter was used for leveling,

laying off right angles, andfor measuring horizontal and vertical angles. Since the

telescope was not yet invented during the time the diopter was used, peep sights

were employed for sighting and in aligning the device.

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Compass

The magnetic compass came into wide use during the 13th century for

determining thedirection of lines and in calculating angles between lines. It was

first introduced for use innavigation. The compass consists of a magnetized steel

needle mounted on a pivot at the center of a graduated circle. The needle

continues to point toward magnetic north and gives a reading which is dependent

upon the position of the graduated circle.

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Gunter's Chain

The Gunter's Chain, which was invented by Sir Edmund Gunter in 1620, was

the forerunner of instruments used for taping distances. It is 66 ft long and

contains 100 links, so that the distances may be recorded in chains and in decimal

parts of the chain. Each part, called a link is 0.66ft long or 7.92 inches.

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Chorobates

This instrument was designed for leveling work. It consisted of a horizontal

staright-edge about 6m long with supporting legs, and a groove 2.5 cm deep and

1.5 m long on top.Water is poured into groove and when the bar is leveled so that

stood evenly in the groove without spilling, a horizontal line is established.

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Merchet

The device for measuring time and meridian. It was first used by the

Chaldeans in about 4,000 B.C. It consisted of a slotted palm leaf through which to

sight and a bracket from whicha plumb bob was suspended. By sighting through

the slot and past the plumb bob string, a straight line could be projected.

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