From 1868 to 1873 he was in charge of a private observatory at Aberdeen, and from 1873-6 of Lord Crawford's observatory at Dunecht, organizing from there the expeditions to Mauritius to observe the transit of Venus in 1874 and to Ascension I.
Here stands the Royal Observatory, in which the great Dunecht telescope was erected in 1896.
It differed only from the three Russian instruments in having a mounting by the Cookes in which the declination circle reads from the eye-end.5 This instrument was afterwards most generously lent by Lord Lindsay to Gill for his expedition to Ascension in 1877.6 These four Repsold heliometers proved to be excellent instruments, 5 For a detailed description of this instrument see Dunecht Publications, vol.
(Philadelphia and London, 1876); Seeliger, Theorie des Heliometers (Leipzig, 18 77); Lindsay and Gill, Dunecht Publications, vol.
(Dunecht, for private circulation, 1877); Gill, Mem.
Of the Dunecht Observatory Publications, 1876).