The Octant
What is remarkable about the octant is the number of persons who independently invented the device in a short period of time. John Hadley and Thomas Godfrey both get credit for inventing the octant. They independently developed the same instrument around 1731. They were not the only ones, however.
In Hadley's case, two instruments were designed. The first was an instrument very similar to Newton's reflecting quadrant. The second had essentially the same form as the modern sextant. Few of the first design were constructed, while the second became the standard instrument from which the sextant derived and, along with the sextant, displaced all prior navigation instruments used for celestial navigation.
Caleb Smith, an English insurance broker with a strong interest in astronomy, had created an octant in 1734. He called it an Astroscope or Sea-Quadrant. He used a fixed prism in addition to an index mirror to provide reflective elements. Prisms provide advantages over mirrors in an era when polished speculum metal mirrors were inferior and both the silvering of a mirror and the production of glass with flat, parallel surfaces was difficult. However, the other design elements of Smith's instrument made it inferior to Hadley's octant and it was not used significantly.
Jean-Paul Fouchy, a mathematics professor and astronomer in France invented an octant in 1732. His was essentially the same as Hadley's. Fouchy did not know of the developments in England at the time, since communications between the two country's instrument makers was limited and the publications of the Royal Society, particularly the Philosophical Transactions, were not being distributed in France. Fouchy's octant was overshadowed by Hadley's.
Read more about this topic: Reflecting Instrument