We give here details of Gregory's observatory which was either the Upper Hall of the University Library or perhaps above it. The text was prepared by Turnbull for the occasion of the Tercentenary:-
In 1673 the University of Gregory's adoption commissioned him to proceed to London to purchase "such instruments and utensils as he . . . shall judge most necessary and useful," and, since funds were inadequate for the purpose, authorised him to make such applications and collections as he saw fit in order that "the fabric and form of the most competent observatory ... may be built" at St Andrews. Gregory went back to the city of his Alma Mater, Aberdeen, in search of funds, and there "a collection [was taken] at the Kirk Dores for the Observatory at Saint Andrews."
A copy in the handwriting of Flamsteed has recently been found, in the Greenwich Observatory, of a letter from Gregory, dated 19 July 1673, in which he seeks advice of Flamsteed concerning instruments for the contemplated observatory at St Andrews. Flamsteed had suggested fitting a wall quadrant of eight foot radius for observational purposes, which Gregory liked "exceedingly." "But" he adds "the Walls of our observatory being already built in the top of one of our Colleges, can admit none such: seeing they decline considerably from the meridian, the matter of 9 or 10 degrees. ... We have in St Andrews a Steeple above 100 foot high, [St Rule's Tower, which stands in the grounds of the ruined cathedral is 109 feet high] plain square work, without any tricket. I desire to know if this Steeple being exactly measured with a chain may not serve for one Place of a very Exact and Large Quadrant, looking exactly with a Telescope."
The College to which the letter refers is evidently the Library building whose length diverges some 9 or 10 degrees from true east and west. The actual observatory was therefore either the Upper Hall or else a still higher room raised in the same block. The letter does not make this entirely clear. Gregory says further that the building was to be 59 feet long, 26 feet wide [The Upper Hall of the Library is 26 feet wide and 76 feet long] and 13 feet high, at which level a "platform" should be "put on, and then towards the North part of it a Chamber should be taken 20 foot square, leaving by the one side an entrance 6 foot broad and 20 foot long to enter the Observatory, which at this rule is 39 foot long and 26 foot broad. We would have it have 6 Windows, 2 on each wall at equal distances from the corners of the Observatory and from each other; each Window should be 4 foot from the floor, 3 foot broad and 9 high to the platform. The North Stars can only be observed from the platform, from which towards the North we can only behold the Sea."
Thus a platform, raised 13 feet above the floor of the observatory, would give the observer a clear view towards the northerly horizon - over South Street and all the buildings further North. This certainly suggest that the actual observatory was on a floor higher than that of the present Upper Hall (which had then a low ceiling). If so, the floor of the observatory was at the level of the present gallery to the Upper Hall.
The word Observatory is used in this letter in 1673, three years earlier than the first quotation in the Oxford English Dictionary. It also occurs in the Commission of the University of St Andrews to James Gregory referred to above.
A few years later and certainly before 1713 a new Observatory was erected outside the University precincts near what was then the Lade Braes path. It was dismantled in 1736 (University Minutes, vol. 4). The site is unmarked today but is near the foot of West Burn Lane, in the roadway on the south side of Queen's Terrace. Standing on the head of the brae which rises from Kinness Burn the Observatory would be in a good position for its purpose. Until about a century ago its ruins remained and are marked on plans of St Andrews which appeared in some local guides until 1845. In or about that year the Lade Braes path, which then extended to the foot of Abbey Street, was repaired and widened at the instigation of Provost Playfair. It is probable that what remained of the Observatory was then razed to the ground, in common with many other objects of historical or architectural interest and importance.