It was a former Archbishop of Armagh, Ussher, who had stated (during the seventeenth century) that the Earth had been created at a definite moment in October, B.C. 4004. Ussher's method was to add up the ages of the patriarchs and make some other equally peculiar calculations. The final result satisfied him completely, and met with wide acceptance at the time; before long his figure for the age of the world was challenged on scientific grounds, but no astronomer would have dared to maintain that the Earth could be as much as a thousand million years old, whereas the modern figure is around 4,700 million years.
	Herschel, by common consent the greatest astronomer of the day, was convinced that there must be intelligent beings on the Moon, the planets, and even inside the Sun; not everyone agreed with him, but he never wavered in his views, and remained faithful to them up to his death in 1822. And in a well-known book on popular astronomy written by James Ferguson, who began life as a shepherd-boy and ended it as a leading scientific writer, we find a section headed "It is highly probable that all the planets are inhabited", which summed up the general opinion at the time. In the edition of Ferguson's book published in 1790, when Armagh Observatory was being completed, there is even a discussion about the habitability of comets.
Ferguson writes 3: that "when we consider the infinite power and goodness of the Deity. . . it seems highly probable that such numerous and large masses of durable matter as the Comets are, however unlike they be to our Earth, are not destitute of beings capable of contemplating with wonder, and acknowledging with gratitude, the wisdom, symmetry and beauty of the Creation". This strikes one as being naive, though it must be borne in mind that modern flying saucer enthusiasts and their kind are equally credulous.

Greenwich had established its reputation; by 1790 it was already regarded as the timekeeping centre of the world. The same sort of work was planned for Armagh, since Flamsteed's star-catalogue was already more than half a century old, and instruments had been considerably improved in the meantime. Moreover, Flamsteed had had to work under serious difficulties when he had become astronomer at Greenwich in 1675, since King Charles' generosity did not extend to the provision of instruments; Flamsteed was expected to obtain these for himself.

Hamilton, on assuming his duties at Armagh in 1790, was entitled to expect far better treatment, and his ability and enthusiasm could not be questioned. He was born in 1748, son of Colonel Gustavus Hamilton of Summerseat in County Meath. He entered Trinity College on 1 November 1764, graduating in 1769; for some years following 1776 he lived at Cookstown, where he Set up a private observatory. On 1 March 1784 he became Treasurer of Armagh Cathedral, an office which he held until he went to the Observatory, and on July 13 of the same yeare he graduated B.D. and D.D. at the University of Dublin. By now he had been transferred to the living of Mullabrack, about six miles from Armagh, but he naturally went to live at the Observatory when he became astronomer there. He was Archdeacon of Ross from 1790 to 1804, when he became Dean of Cloyne; By the standards of his time he was well off financially; it is said that he travelled around in the comfort of a coach and four, and that he subsequently adopted the practice of spending the summers at Mullabrack (where he had installed two curates to attend to local church duties) and the winters at Armagh. His home life appears to have been happy. In addition to his daughter Julia he had two wards, Catherine and Juliana Tisdall, who, it is said, frequently entertained their young suitors in the Observatory dome.

A Ramsden transit instrument ended up in Moscow, and the meridian circle in Palermo, from an ordered meridian circle, which was offered by the Admiralty for the construction of a chronometer. The Observatory obtained no instrument for polar distances except Troughton's equatorial, by no means capable of entering into the field with large meridian circles. The Troughton equatorial arrived in December 1795, and was mounted under the dome on two stone piers which rested on a massive pillar. The mounting was itself extremely massive, and of what is termed the English type; for its period it was extremely efficient - and yet the object-glass of the telescope had an aperture of only 2.5 inches and a focal length of three feet. By modern standards this is puny indeed, but for a long time it represented Armagh's main equipment. It was used for general observations, and with it Hamilton and his assistants determined the declinations of 37 standard stars; the results were published by Pond, afterwards Astronomer Royal, in 1806.