formed my plan, requesting him to correct it where it was wrong. He returned
me a most polite and friendly answer, although I had never seen him during my
stay at Edinburgh, and informed me, that I had only mistaken the radical mean place of the ascending node by a quarter of a degree; and that if I would send the drawing of my rotula to him, he would examine it, and endeavour to procure me a subscription to defray the charges of engraving it on copper-plates, if I chose to publish it. I then made a new and correct drawing of it, and sent it to him: who soon got me a very handsome subscription, by setting the example himself, and sending subscription papers to others.
I then returned to Edinburgh, and had the rotula-plates engraved there by Mr Cooper.[1] It has gone through several impressions; and always sold very well till the year 1752, when the style was changed, which rendered it quite useless. Mr Maclaurin received me with the greatest civility when I first went to see him at Edinburgh. He then became an exceeding good friend to me, and continued so till his death.
One day I requested him to show me his orrery, which he immediately did; I was greatly delighted with the motions of the earth and moon in it, and would gladly have seen the wheel-work, which was concealed in a brass box, and the box and planets above it were surrounded by an armillary sphere. But he told me, that he never had opened it; and I could easily perceive that it could not be opened but by the hand of some ingenious clock-maker, and not without a great deal of time and trouble.
After a good deal of thinking and calculation, I found that I could contrive the wheel-work for turning the planets in such a machine, and giving them their progressive motions; but should be very well satisfied if I could make an orrery to show the motions of the earth and moon, and of the sun round its axis. I then employed a turner to make me a sufficient number of wheels and axles, according to patterns which I gave him in drawing ; and after having cut the teeth in the wheels by a knife, and put the whole together, I found that it answered all my expectations. It showed the sun's motion round its axis, the diurnal and annual motions of the earth on its inclined axis, which kept its parallelism in its whole course round the sun ; the motions and phases of the moon, with the retrograde motion of the nodes of her orbit; and consequently, all the variety of seasons, the different lengths of days and nights, the days of the new and full moons, and eclipses.
When it was all completed except the box that covers the wheels, I showed it to Mr Maclaurin, who commended it in presence of a great many young gentlemen who attended his lectures. He desired me to read them a lecture on it, which I did without any hesitation, seeing I had no reason to be afraid of speaking before a great and good man who was my friend. Soon after that, I sent it in a present to the reverend and ingenious Mr Alexander Irvine, one of the ministers at Elgin, in Scotland.
I then made a smaller and neater orrery, of which all the wheels were of ivory, and I cut the teeth in them with a file. This was done in the beginning of the year 1743; and in May, that year, I brought it with me to London, where it was soon after bought by Sir Dudley Rider. I have made six orreries since that time, and there are not any two of them in which the wheel- work is alike, for I could never bear to copy one thing of that kind from another, because I still saw there was great room for improvements.
I had a letter of recommendation from Mr Baron Eldin at Edinburgh, to the right honourable Stephen Poyntz, Esq. at St James's, who had been precep-
- ↑ Cooper was master to the justly celebrated Sir Robert Strange, who was at that time his apprentice.
