Mountbatten Medallic History of Great Britain and the Sea Medal:Hadley's Quadrant and Cunigham'…

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Mountbatten Medallic History of Great Britain and the Sea Medal:Hadley's Quadrant and Cunigham's Telescope

AssociatedAssociated with Lord Mountbatten of Burma (Frogmore House, Windsor, England, 1900 - 1979)

Medallist John Pinches, Medallists

DateMay 2004

Object NameMedal

MediumSterling Silver

ClassificationsMedals

Dimensions44mm

AcquisitionPresented in 2004 by Dr Joan M Burrell.

LocationView by Appointment - Aberdeen Treasure Hub

Object numberABDMS072500.22

Keywords

About MeThe Hadley quadrant is a navigator's instrument for measuring the altitude of the sun or a star above the horizon, up to an angle of 90°. First described by John Hadley (1682-1744) to the Royal Society in 1731 it quickly became popular with seamen and remained in use until the latter half of the 19th century. It replaced Davis's backstaff as a key instrument aiding British expansion at sea.

Hadley's instrument measured up to one-quarter of a circle or 90° on the principle of double reflection, the actual arc of the instrument being only one-eighth of a circle. In consequence it is often called an octant.

The first octants were made with a hard-wood frame and index arm, the scale being of boxwood engraved by hand with a diagonal scale. In order to obtain accuracy the scale was large and the instrument of from 18 inches to 22 inches long.

Later improvements in scale dividing techniques, by Jesse Ramsden and others, allowed the overall size of the instrument to decrease to about 9 inches.

The more expensive and more accurately constructed sextant, able to measure angles up to 120° was developed from the octant in about 1758 and remains in use today virtually unchanged from the original design.

Jacob Cuningham's telescope is the oldest known dated telescope and is constructed of leather covered wood with papiermâché draw tubes on the simple Galilean system of lenses.

Refracting telescopes are said to have been invented in Holland in about 1608, although some historians attributed their invention to the 16th century. They quickly became popular with military officers and seamen. Due to the poor quality of optical glass and the primitive methods of grinding and polishing lenses, early telescopes were of low power and long focal length. In consequence they were lightly constructed to reduce weight, but still unwieldy in use. Nevertheless they played an all important part in seafaring for more than a century.

During the I750s John Dollond patented the achromatic object lens constructed of two different types of glass which reduced the effect of chromatic aberration (rainbow-like colours seen around the image) and allowed shorter more durable telescopes to he constructed.

Jacob Cuningham's telescope was probably made in Holland and magnifies about three times, the low power accounting for its comparatively short length.

The Mountbatten Medallic History of Great Britain and the Sea, John Pinches Medallists Ltd.