Hadley, J.

…It was based on the same optical principles as the sextant and was used in the same way, but the scale was 1/8 of the circumference and sighting was done with the naked eye. The octant is also called Hadley's quadrant and was invented by the British mathematician J. Hadley (1682-1744). The octant was the forerunner of the sextant, but the more sophisticated sextant became more widespread. …

*Some of the terminology that mentions "Hadley, J." is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…六分儀と同じ光学原理に基づき使い方も同じであるが，目盛環は円周の1/8で視準は肉眼で行った。八分儀はハドリーの象限儀ともいわれ，イギリスの数学者ハドリーJ.Hadley(1682‐1744)の考案になる。八分儀は六分儀の先駆となったが，より精巧な六分儀が普及した。…

※「Hadley，J.」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報