Sextants

Sextant

The picture is of a sextant. For anyone who doesn't know, it's nothing raunchy (sexual tantricity, perhaps? no). "Sex" means "a sixth" in this case, as the device is made up of one sixth of a full circle.

The sextant is a device that was originally developed to aid in the task of nautical navigation. It was originally invented by Godfrey and Hadley when, in 1715, the British Government offered large cash prizes for anyone who could solve their navigation problems. Taking inspiration from Sir Isaac Newton and other physicists, they developed the sextant and were awarded the prize.

The sextant may look daunting, but compared to its precursors like astrolabes and quarterstaves, it is more accurate and accessible to the user. To begin, the user looks through the eyepiece and aligns the device with the horizon. Through the eyepiece they will see the horizon. Then they must turn the index mirror until they see the sun, for example, in one half of the mirror. When the sun and the horizon are aligned, the angle between the first object, the user, and the second object will be indicated on the arc. There are no electronics involved, it is entirely mechanical.

This is probably one of the things I like most about the sextant. I am often amazed when analog devices like this achieve high levels of accuracy. Despite the fact that this machine uses somewhat simple geometry, and is entirely mechanical, it is really powerful. It can be used to find ones longitude and lattitude, with reference to the stars; to measure distances via trigonomotry; time, by reference again to the sun and stars, all with a bit of maths. And of course angles, to any degree of accuracy depending on the mirror surface, the scales used, and the accuracy of the geometry. Sundials, sextants, calipers... these mechanical measurers of such high accuracy and such old origin never cease to impress me.

Scott Everitt

Sources:
http://www.clipperlight.com/howusesextant.html
http://the-rex-of-kings.com/products/marine_sextant