After my first post on this topic, I serendipitously came across a 1958 copy of Munro's Navigation (from which the above images are taken) in a thrift store. Unsurprisingly, there's an entire chapter devoted to the sextant. It really is a complicated device. I've uploaded the chapter here: The Sextant
The "Sea Safe Bell Sextant" pictured above carries the label "Hezzanith" and the maker's name: "Heath and Sons." According to the Museum of the History of Science, Oxford:
Hezzanith was a brand patented by Heath & Co., a company founded by George Heath in New Eltham, London in 1845. In 1863 his son George Wilson entered the firm as an apprentice and in 1872 he eventually took over the company. The business manufactured scientific surveying instruments and maritime navigation devices. They had a showroom in London and a factory, The Observatory Works, in Kent. In 1937, Heath & Co. was acquired by the prestigious firm W. F. Stanley & Co.
(The Stanley firm of London England was founded in 1853 by William Ford Robinson Stanley, an amazing engineer and inventor. It became part of the Sime Darby Group around 1977 and was finally liquidated in 1999.)