[4] It would seem that Gill's interests lay elsewhere since after a few years he sold the business, and then spent time equipping Lord Lindsay's private observatory at Dun Echt, Aberdeenshire.

While carrying out these laborious calculations, he was notified of his appointment to the Cape Observatory, which, over the following 27 years he was to refurbish completely, turning it into a first-rate institution.

The invention of dry plate photography by Richard Leach Maddox made Gill realise that the process could be used to create images of the stars and to more easily determine their relative positions and brightness.

This led to a massive project in collaboration with the Dutch astronomer J.C. Kapteyn, and the compiling of an index of brightness and position for some half a million southern stars.

Gill also played a leading role in the organising of the Carte du Ciel, an ambitious international venture aimed at mapping the entire sky.

[7] As president of the British Association for the Advancement of Science, he gave a presidential address in 1907 in which he advocated definitions based on fundamental physical properties, rather than on arbitrary standards such as a rod of metal with lines ruled upon it to mark the yard or metre.