The bubble octant and bubble sextant are

air navigation The basic principles of air navigation are identical to general navigation, which includes the process of planning, recording, and controlling the movement of a craft from one place to another. Successful air navigation involves piloting an airc ...

instruments. Although an instrument may be called a "bubble sextant", it may actually be a bubble octant.

Use

Ships had long used

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 cel ...

s for

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

, but sextants had problems in aircraft navigation. A ship at sea is on a relatively flat surface and can use the

horizon The horizon is the apparent curve that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This curve divides all viewing directions based on whethe ...

to measure the altitude of celestial objects. However, an aircraft may not have the sea's horizon as a flat reference surface. It may be flying over land where the horizon is formed by mountains of unknown height. A solution to the problem was to use a bubble to determine the reference plane. The bubble in an airplane is subject to the plane's acceleration. If the plane is in sharp turn, the bubble will be displaced. Consequently, when the navigator is using a bubble sextant, the pilot tries to fly the plane straight and level. Even when flying straight, a plane is subject to acceleration from

air density The density of air or atmospheric density, denoted '' ρ'', is the mass per unit volume of Earth's atmosphere at a given point and time. Air density, like air pressure, decreases with increasing altitude. It also changes with variations in atmosph ...

and wind changes. Consequently, use of a bubble octant requires many readings be taken and then averaged for a more accurate result. Some bubble octants have accessories to make the averaging simpler.

Development

Isaac Newton Sir Isaac Newton () was an English polymath active as a mathematician, physicist, astronomer, alchemist, theologian, and author. Newton was a key figure in the Scientific Revolution and the Age of Enlightenment, Enlightenment that followed ...

developed the

quadrant Quadrant may refer to: Companies * Quadrant Cycle Company, 1899 manufacturers in Britain of the Quadrant motorcar * Quadrant (motorcycles), one of the earliest British motorcycle manufacturers, established in Birmingham in 1901 * Quadrant Privat ...

. The octant was a further improvement. It could measure altitudes of up to 90° above the horizon. The first bubble instruments, which were developed by

Gago Coutinho Carlos Viegas Gago Coutinho, GCTE, GCC (; 17 February 1869 – 18 February 1959), generally known simply as Gago Coutinho, was a Portuguese geographer, cartographer, naval officer, historian and aviator. An aviation pioneer, Gago Coutinho and ...

, were bubble sextants that copied the features of an ordinary sextant.

Use

Development

See also