Bris sextant. Assembly drawing of a Bris sextant. The Bris sextant is not a

sextant A sextant is a doubly reflecting navigation instrument that measures the angular distance between two visible objects. The primary use of a sextant is to measure the angle between an astronomical object and the horizon for the purposes of celes ...

proper, but is a small angle-measuring device that can be used for navigation. The ''Bris'' is, however, a true

reflecting instrument Reflecting instruments are those that use mirrors to enhance their ability to make measurements. In particular, the use of mirrors permits one to observe two objects simultaneously while measuring the angular distance between the objects. While re ...

which derives its high accuracy from the same principle of double reflection which is fundamental to the octant, the true sextant, and other reflecting instruments. It differs from other sextants primarily in being a fixed angle sextant, capable of measuring a few specific angles. Sven Yrvind (Lundin) developed his Bris sextant as part of his quest for low-cost, low-technology equipment for ocean crossings. The ''Bris'' is a low-technology, high-precision, fixed-interval instrument. It is made of two narrow, flat pieces of glass (

microscope slide A microscope slide is a thin flat piece of glass, typically 75 by 26 mm (3 by 1 inches) and about 1 mm thick, used to hold objects for examination under a microscope. Typically the object is mounted (secured) on the slide, and then b ...

s) permanently and rigidly mounted in a V-shape to a third flat piece of #12 welding glass to make viewing the sun eye safe. When the sun or moon is viewed through the V, it is split into eight images. The instrument is small and rugged enough that it can be kept in a 35mm film canister (about 2 cm radius, 3 cm tall) on a lanyard around one's neck. The Bris sextant is calibrated at a known geographic position with a good clock and a

nautical almanac A nautical almanac is a publication describing the positions of a selection of celestial bodies for the purpose of enabling navigators to use celestial navigation to determine the position of their ship while at sea. The Almanac specifies for ea ...

. As the day passes, one works the sight reductions backwards to develop exact angles for each of the images' tops and bottoms. The

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

and

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

have approximately the same

angular size The angular diameter, angular size, apparent diameter, or apparent size is an angular distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it is ...

from the surface of the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, and can use the same

calibration In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of know ...

s. In use, one waits until an image's edge touches the horizon, and then records the time and reduces the sight using the recorded angle for that edge of the image.

Etymology

''Bris'' is Swedish for ''breeze''. It would appear that the name ''Bris'' is used by Yrvind for a number of his sail boats and is a favourite of his.

References

External links

The home page of Mr Sven Yrvind
and his autobiography in Swedish, "Konstruktören" ("The Constructor"), . *{{cite web , url = http://www.yrvind.com/sextant_read_more.html , title = More about my Bris sextant , last = Yrvind , first = Sven , accessdate = 2013-08-12 , archive-url = https://web.archive.org/web/20131013001940/http://www.yrvind.com/sextant_read_more.html , archive-date = 2013-10-13 , url-status = dead

four-page academic article describing the principles of the Bris sextant.
Cassens-Plath catalogue
showing a two-page description of the Bris sextant. *A three-page article (not available online) on the Bris sextant appeared i
Yachting Monthly
magazine, June 1997. *A two-page article (not available online) on the Bris sextant appeared i
Die Yacht
magazine, 22/1997: ''Mini-Sextant: Mit einem genial einfachen Gerät verblufft Weltumsegler Sven Lundin jetzt die gesamte Fachwelt.''
Determination of latitude by two fixed altitude sightings
with a Bris sextant. Brian Villmoare, 2022, The Journal of Navigation. Navigational equipment Celestial navigation Astronomical instruments