Dr. Duncan was born in the city of St. Andrews, upon the 17th October, 1744, and received his education at the University there. Having determined to follow medicine as his profession, he repaired to Edinburgh, and completed his studies under the superintendence of the medical teachers of that city. He early attached himself to the Medical Society, which was instituted in the year 1737. While a member he took an active part in its business, was for many years treasurer, and several times elected one of its presidents. The propriety and advantages of a Hall, the foundation-stone of which was laid by Di\ Cullen in 1770, was originally suggested by Dr. Duncan, under whose inspection and management it was subsequently erected. In testimony of the sense entertained of the value of his services, a gold medal was voted to him in 1787, and his full-length portrait, painted at the expense of the society, was afterwards placed in the Hall.

In 1768-9, Mr. Duncan went a voyage to China, as Surgeon of the East India Company's ship Asia, under the command of Mr., afterwards Sir Robert Preston. His services were so highly esteemed in this capacity, that the Captain offered him .£500 to go out with him a second time. This he declined.

In October, 1769, Mr. Duncan took the degree of Doctor of Medicine at the University of St. Andrews; and in the month of May following he was admitted a licentiate of the Royal College of Physicians. At what period he had projected the plan of delivering private lectures on medicine in Edinburgh is not exactly known. It was considered a great novelty, because at that time there had been only once instance of an attempt to deliver medical lectures without the bounds of the University. This was by Dr. George Martin, also a physician from St. Andrews. He commenced about twelve or fifteen years previous to Dr. Duncan. Whether he delivered a second course is unknown, for he was very soon removed by death. Dr. Duncan for many years gave lectures on different branches of medicine.

Whilst busily engaged in preparing for the commencement of his lectures, a vacancy having occurred in the University of St. Andrews, by the death of Dr. Thomas Simson, Professor of Medicine, Dr. Duncan immediately resolved to stand for the chair, which is in the gift of the University. On this occasion he produced ample testimonials from the medical gentlemen of the University of Edinburgh, under whom he had studied, as well as other equally satisfactory recommendations. He was nevertheless unsuccessful. This occurred in 1770. Without relaxing his diligence during the course of that year, he published a syllabus of what he proposed to discuss more fully in his lectures. It was entitled "Elements of Therapeutics."

In 1772, Dr. Duncan published an essay on the use of Mercury. On the 6th September, 1775, he was appointed by the patrons to teach the class of the Institutes of Medicine, in the place of Dr. Drummond, at that time abroad. He at the same time announced himself a candidate, in the event of Dr. Drummond declining to accept of the professorship. It is now generally acknowledged that Dr. Duncan was not fairly treated in this transaction by the magistrates, who thought proper to pass him over. At the commencement of the Session, in November, 1776, he published an address to the students of medicine in the University, in which he stated his intention to continue his lectures out of the College. About this time he also gave to the public "Heads of Lectures on the Theory and Practice of Medicine." His classes were well attended; and his not obtaining the professorship increased in place of diminishing the number of students.

The Doctor had the merit of founding, in the same year, the Edinburgh Dispensary. The plan and the execution of it originated with himself. An Infirmary had been erected about forty years before that period; but persons afflicted with what are termed chronic diseases are not admitted into it, though they have a very strong claim upon the sympathy and compassion of mankind. The labour and exertion to which he submitted in accomplishing the object intended were unremitting. He drew up a prospectus; and, after circulating it among his friends, and securing their approbation, he adventured to address the public upon the subject, which was favourably received. A Hall was erected in West Richmond Street, with suitable accommodation. In it there is a portrait of the founder, painted for the Dispensary by the late Sir Henry Raeburn. The Doctor lived long to see his generous labours crowned with success; and, at the interval of half a century, to have the agreeable information communicated, that upwards of two hundred thousand patients had derived benefit from the institution.

Dr. Duncan entered warmly into every proposal which had for its object the promotion of medical science. He projected, in 1773, a new work to be published annually, originally under the name of " Medical Commentaries," but subsequently under the title of " Annals of Medicine," which regularly made its appearance for a series of more than thirty j'ears.

The celebrated Dr. Cullen, through old age and extreme debility, having resigned, Dr. James Gregory was elected to the professorship of the Practice of Physic, on the 30th December, 1789. Upon the same day Dr. Duncan was chosen Dr. Gregory's successor; and he taught this class—"The Theory of Medicine"—till within a few months of his death.

Dr. Duncan, delighted much in the pleasure of a garden, and having for many years entertained an opinion that the science of horticulture might be greatly improved, he succeeded, in 1809, in establishing the Caledonian Horticultural Society. It is incorporated by Royal charter, and, by exciting a spirit of emulation among practical gardeners, has been productive of the best effects. Upon the death of Dr. Gregory, lie was appointed, in 1821, First Physician to his Majesty for Scotland.

The practice of visiting Arthur's Seat early on the morning of the 1st of May, is, or rather was, observed with great enthusiasm by the inhabitants of Edinburgh. Dr. Duncan was one of the most regular in his devotions to the Queen of May, during the long period of nearly fifty years; and to the very last he performed his wonted pilgrimage with all the spirit, if not agility, of his younger years. These visits he not infrequently celebrated by some poetic production, which he transmitted to his friends. On the 1st Ma}', 1820, two years before his death, although aged eighty-two, he paid his annual visit; and, on the summit of the hill, read a few lines of an address to Alexander, Duke of Gordon, then the oldest Peer alive. To this the Duke furnished a reply; and, as a memorial of the transaction, Dr. Duncan had both effusions lithographed and circulated among his friends, with this inscription:—"Lithographic Facsimile of the Handwriting of two Octogenarians." One page is the production of the Doctor, the other of the Duke:—

I. "An octogenarian physician at Edinburgh, who has been long in the habit of walking to the top of Arthur's Seat, at an early hour on the morning of May-day, took his wonted pedestrian exercise on Monday, the 1st May, 1826. He read to numerous hearers on the top of the hill the following short poetical address to the oldest Duke in Scotland:—

"Once more, good Duke, my duty to fulfil,
I've reached the summit of this lofty hill,
To thank my God for all his blessings given,
And by my prayers, to aid my way to heaven.
Long may your Grace enjoy the same delight,
Till to a better world we take our flight."