A kamal, often called simply ''khashaba'' (wood in Arabic), is a

celestial navigation Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space (or on the surface of ...

device that determines

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...

. The invention of the kamal allowed for the earliest known latitude sailing, and was thus the earliest step towards the use of

quantitative Quantitative may refer to: * Quantitative research, scientific investigation of quantitative properties * Quantitative analysis (disambiguation) * Quantitative verse, a metrical system in poetry * Statistics, also known as quantitative analysis ...

methods in

navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...

. It originated with Arab navigators of the late 9th century, and was employed in the

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by th ...

from the 10th century. It was adopted by Indian navigators soon after, and then adopted by Chinese navigators some time before the 16th century.

Description

Since the

Polaris Polaris is a star in the northern circumpolar constellation of Ursa Minor. It is designated α Ursae Minoris ( Latinized to ''Alpha Ursae Minoris'') and is commonly called the North Star or Pole Star. With an apparent magnitude that ...

is currently close to the celestial pole, its elevation is equal to the latitude of the observer. The kamal consists of a rectangular wooden card about , to which a string with several equally spaced knots is attached through a hole in the middle of the card. The kamal is used by placing one end of the string in the teeth while the other end is held away from the body roughly parallel to the ground. The card is then moved along the string, positioned so the lower edge is even with the horizon, and the upper edge is occluding a target star, typically

because its angle to the horizon does not change with longitude or time. The angle can then be measured by counting the number of knots from the teeth to the card, or a particular knot can be tied into the string if travelling to a known latitude. Kamal Polaris Side

The knots were typically tied to measure angles of one finger-width. When held at arm's length, the width of a finger measures an angle that remains fairly similar from person to person. This was widely used (and still is today) for rough angle measurements, an angle known as ''issabah إصبع'' in

Arabic Arabic (, ' ; , ' or ) is a Semitic languages, Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C ...

or a ''zhi'' 指 in Chinese (both meaning 'finger'). By modern measure, this is about 1 degree, 36 minutes, and 25 seconds, or just over 1.5 degrees. It is equal to the

arcsine In mathematics, the inverse trigonometric functions (occasionally also called arcus functions, antitrigonometric functions or cyclometric functions) are the inverse functions of the trigonometric functions (with suitably restricted domains). Spec ...

of the ratio of the width of the finger to the length of the arm. In Chinese navigation, the unit of ''jiao'' 角 is also used to represent a quarter 指 (an angle of 24 minutes 6 seconds). Due to the limited width of the card, the kamal was only really useful for measuring Polaris in equatorial latitudes, where Polaris remains close to the horizon. This fact may explain why it was not common in Europe. For these higher-latitude needs somewhat more complex devices based on the same principle were used, notably the

cross-staff The term Jacob's staff is used to refer to several things, also known as cross-staff, a ballastella, a fore-staff, a ballestilla, or a balestilha. In its most basic form, a Jacob's staff is a stick or pole with length markings; most staffs ar ...

and

backstaff The backstaff is a navigational instrument that was used to measure the altitude of a celestial body, in particular the Sun or Moon. When observing the Sun, users kept the Sun to their back (hence the name) and observed the shadow cast by the u ...

. The kamal is still a tool recommended for use in

sea kayak A sea kayak or touring kayak is a kayak developed for the sport of paddling on open waters of lakes, bays, and the ocean. Sea kayaks are seaworthy small boats with a covered deck and the ability to incorporate a spray deck. They trade off the man ...

ing.Burch, David, ''Fundamentals of Kayak Navigation'', 2nd edition, The Globe Pequot Press, 1993, In such an application, it can be used for estimating distances to land. The distance can be calculated from the formula :

D=\frac

where

D

is the distance to the object,

S

is the size of the object observed,

d

is the distance from the kamal to the observer's eye, and

s

is the size of the kamal.

Notes

References

* Carreiro, Carlos B., ''Portugal's Golden Years, The Life and Times of Prince Henry "The Navigator"''. Dorrance Publishing Co., p. 84 * Malhão Pereira, J.M. (2003), "The Stellar Compass and the Kamal. An Interpretation of its Practical Use", in ''Proceedings of the International Seminar on Marine Archeology'', Delhi, also published by Academia de Marinha (Lisbon, 2003). *{{Citation , last=McGrail , first=Sean , year=2004 , title=Boats of the World , publisher=

Oxford University Press Oxford University Press (OUP) is the university press of the University of Oxford. It is the largest university press in the world, and its printing history dates back to the 1480s. Having been officially granted the legal right to print books ...

, isbn=0-19-927186-0 Navigational equipment Celestial navigation Orientation (geometry) Measuring instruments Arab inventions

Description

See also

Notes

References