Page:A biographical dictionary of eminent Scotsmen, vol 3.djvu/270

298 astronomy out of my mind; and I had no inclination to become .acquainted with any one there who taught either mathematics or astronomy, for nothing would serve me but to be a doctor.

At the end of the second year I left Edinburgh, and went to see my father, thinking myself tolerably well qualified to be a physician in that part of the country, and I carried a good deal of medicines, plaisters, &c. thither; but to my mortification I soon found that all my medical theories and study were of little use in practice. And then, finding that very few paid me for the medicines they had, and that I was far from being so successful as I could wish, I quite left off that business, and began to think of taking to the more sure one of drawing pictures again. For this purpose I went to Inverness, where I had eight months' business.

When I was there, I began to think of astronomy again, and was heartily sorry for having quite neglected it at Edinburgh, where I might have improved my knowledge by conversing with those who were very able to assist me. I began to compare the ecliptic with its twelve signs, through which the sun goes in twelve months, to the circle of twelve hours on the dial-plate of a watch, the hour-hand to the sun, and the minute hand to the moon, moving in the ecliptic, the one always overtaking the other at a place forwarder than it did at their last conjunction before. On this, I contrived and finished a scheme on paper, for showing the motions and places of the sun and moon in the ecliptic on each day of the year, perpetually; and consequently, the days of all the new and full moons.

To this I wanted to add a method for showing the eclipses of the sun and moon; of which I knew the cause long before, by having observed that the moon was for one half of her period on the north side of the ecliptic, and for the other half on the south. But not having observed her course long enough among the stars by my above-mentioned thread, so as to delineate her path on my celestial map, in order to find the two opposite points of the ecliptic in which her orbit crosses it, I was altogether at a loss how and where in the ecliptic, in my scheme, to place these intersecting points: this was in the year 1739.

At last, I recollected that when I was with 'squire Grant of Auchoynaney, in the year 1730, I had read, that on the 1st of January, 1690, the moon's ascending node was in the 10th minute of the first degree of Aries; and that her nodes moved backward through the whole ecliptic in 18 years and 224 days, which was at the rate of 3 minutes 11 seconds every 24 hours. But as I scarce knew in the year 1730 what the moon's nodes meant, I took no farther notice of it at that time.

However, in the year 1739, I set to work at Inverness ; and after a tedious calculation of the slow motion of the nodes from January 1690, to January 1740, it appeared to me, that (if I was sure I had remembered right) the moon's ascending node must be in 23 degrees 25 minutes of Cancer at the beginning of the year 1740. And so I added the eclipse part to my scheme, and called it, the Astronomical Rotula.

When I had finished it, I showed it to the Rev. Mr Alexander Macbean, one of the ministers at Inverness; who told me he had a set of almanacs by him for several years past, and would examine it by the eclipses mentioned in them. We examined it together, and found that it agreed throughout with the days of all the new and full moons and eclipses mentioned in these almanacs; which made me think I had constructed it upon true astronomical principles. On this, Mr Macbean desired me to write to Mr Maclaurin, professor of mathematics at Edinburgh, and give him an account of the methods by which I had