Robert Main as chief assistant at the Royal Greenwich Observatory, and at once undertook the fundamental task of improving astronomical constants.
His first task on taking up this post was the reduction and publication of a large mass of observations left by his predecessor, from a selected portion of which (those made 1856–1860) he compiled a catalogue of 1,159 stars.
His principal work was, however, a catalogue of 12,441 stars to the 7th magnitude between the South Pole and 25°S declination, which was practically finished by the end of 1878 and published in 1881.
[2] Shortly after the death of Main on 9 May 1878, Stone was appointed to succeed him as Radcliffe Observer at Oxford, and he left the Cape on 27 May 1879.
He was elected President of the Royal Astronomical Society (1882–1884), and he was the first to recognize the importance of the old observations accumulated at the Radcliffe Observatory by Hornsby, Robertson and Rigaud.