Your Civil Return to Mr Collins hath Emboldened me to Prosecute that further with you; which he freelye Undertook upon my desire. I doe esteem it none of the least advantages of our Universityes desighn; That I have had the good Fortune, to Enter a Correspondence with one so knowinge and Experienced in these things as yourselfe; having a Commission for such a noble designe; And beinge altogether ignorant and without Experience in the most Considerable thinges belonginge to it:
Your first Concerninge a wall Quadrant, of mat: 8 foot in the Radius, I doe like Exceedinglye: But the Walls of our Observatorye beinge allready built in the top of one of our Colledges, can admit none such; seeing they decline Considerablye from the meridian; the mater of 9 or 10 degrees. Neither doe I find the Artificers here willinge to undertake the makinge of a large Quadrant; For none of them hath made above 3 or 4 Foot: Upon this account I am causinge them to make one of 4 foot Radius. And I have Got another from the Duke of Lauderdale 2 Foot Radius. We have in Saint Andrews a Steeple above 100 foot high, plain Square Work, without any Pricket: I desire to know, if this Steeple beinge exactly measured with a Chaine, may not serve for one Place of a verye Exact, and large Quadrant, lookinge Exactlye with a Telescope When a Starr is seen over any sight placed on Top of it, etc. I need not insist in the Place of Sex-tants.
Mr Hooke was shewinge me an Invention which I liked well; viz Two Telescopes moving upon 1 Axis; like the Legs of a Sector with a Line of Chords betwixt the other Ends on which the Telescopes may move 40° and again, Onlye in place of the line of Chords. I should rather Like an Arch Equallye divided; because in this an errour of the Division is easilye Perceived. Mr Hooke tells me that he hath a waye easilye to Mannage this Instrument; which I have not yet seen. This may also serve for a Large Quadrant: For the Telescopes may be of Brasse streight and well Squared 6 or 7 foot longe. I have 2 Pendulum Clocks making, with longe Swinges, Vibratinge Seconds; and Pointinge Houres, Minits and seconds, without Strikinge; And also one little Pendulum Clock, with a short Pendulum, vibratinge 4 times in a Second, alsoe without Strikinge; for discerninge small Intervalls; when there may be a pointe of a Second in Question. As for telescopes Mr Cock is makinge one of an 100 Foot, which I minde to take, if Mr Hook can Shew me to mannage it, as he Promiseth. I thinke our Steeple which I latelye mentioned may helpe me in this. Mr Cock hath one (as he saith to me) by him, of 50 Foot, which I mind also to take: For I think it may be mannaged upon the Platforme above the observatorye. I do not Expect to mannage in the Observatorye any above 20 or 25 Foot; There is nothinge that I am more Curious for than Micrometrers; For I perceive by some things, That I have seen of yours, that you understand Extraordinarilye to mannage. I Intreat you to be very particular Concerninge them; I am also afraid that our Stock will not hold out with Tychos-Armillae, neither were it easie to Carrye them to Scotland unspoyled. There are none understandinge of these things here, of whom I have yet heard, that Ever did see an Observatorye Compleat in their life; And therefore I hope that I may desire you ever to use freedom in that, or if you please to helpe my rude notions of it; We have alreadye a Room 3 Storyes high, declininge in length of it some degrees from the meridian. The rest of the Colledge is betwixt it and the North, it hath the Horizon free upon the South; East and West, onlye some little Mountains at some Miles distance. Of this (beinge as we all judge the fittest Place and least Expence) we are resolved to make our Observatorye. It is in length 59 Feet, in Breadth 26. We were judginge ourselves, that the roof should be Taken of; and the walls heightened above the floor 13 foot; and then a platforme to be put on. And then towards the North part of it A chamber should be taken of 20 foot square; Leavinge by the one side a Entrance 6 foot broad and 20 Longe to enter the observatory which, at this rule, is 39 foot longe and 26 broad. We would have it have 6 Windows, 2 on Each Wall, at aequall 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 Starrs can onely be observed from the Platforme; from which towards the North; We can onely behold the Sea. Any thinge else I need not mention, as a large opening in the Plateforme; for takinge Instruments up from the Observatorye, etc. I hope you will Excuse and take in good part this freedome I have used with you, in desiringe your Judgement, and puttinge you to trouble on so small an Acquaintance; If ever I be so happye as to be in a Capacitye to serve you, you may with all Confidence imaginable assure your self of him who is, Your humble Servant, James Gregorie.
If you shall be pleased to honor me with an answer You may be pleased to direct it to Mr Collins Who will send it to me. J:G.
On 26 July 1673, Flamsteed had his advice on what instruments Gregory should buy sent to Collins as Gregory as asked.
Flamsteed was appointed Astronomer Royal in March 1675 by Charles II and the Royal Observatory at Greenwich began to be built.
On 30 April 1674 Gregory wrote to Colin Campbell [Minister at Archatton] giving some details of the instruments he had bought:-
I am sorrie for my misfortun in loosing your companie whill ye wer here. It were tedius to write down particularlie all the instruments I have brought home, yea a larger letter wold not contein all ther names and sizes, for I have all sort: our largest quadrant is of oak, covered with brasse, 4 foot in radius and actually divided in minutes, of which we can judge 1/3 or 1/4: we have two semisextans, all of brasse, 6 foot in radius, diagonally divided, in which wee can judge 1/6 or 1/7 of a minut. Our largest telescope is 24 foot longe; which magnifys one dimension of the object 100 times. ... As for observations or experiments, I dar hardlie promise anie considerable befor the observatorie be builded: seeing (whill the instruments ar keeped in the bibliotheck, wher I cannot be alon or with my own companie and conveniencie) it is hard if it be at all practicable to doe anie thing seriouslie and with exactnes. The latitude here is 56° 22'. The declination of the needle is 3° 35' westward.