John Walker, Doctor of Divinity, was born in the Canongate of Edinburgh. His father—Hector of the grammar school there—was an excellent classical scholar, and is said to have bestowed such attention to the education of his son, that when ten years of age he could read Horner with considerable fluency. At a proper age, he entered the University, where he studied with merited approbation, and was iu due course of time licensed to preach by the Presbytery of Edinburgh.

Dr. Walker's first presentation was to the parish of Glencorse, about seven miles to the south of Edinburgh, and which includes part of the Pentland Hills within its range. Here an excellent opportunity presented itself to the young clergyman for improvement in his favourite study of botany—a science to which he had been early attached, and in which he had already made considerable progress, as well as in other branches of natural history. In this sequestered and romantic district Dr. Walker passed some of the pleasantest years of his life. Those hours which he could spare from his pastoral duties were generally spent in exploring the green hills of the Pentlands, and in making additions to his botanical specimens.

This pleasing pursuit could of course only be prosecuted during the spring and summer months, but the winter was not without its amusements. The talents and acquirements of Dr. Walker were not allowed to remain unnoticed by the more distinguished of his neighbours and parishioners. Among these were, William Tytler, Esq., of Woodhouselee, well-known for his historical researches, particularly into that portion of Scottish history which relates to Mary Queen of Scots; James Philp, Esq., of Greenlaw, Judge of the High Court of Admiralty; and Sir James Clerk, Bart., of Pennycuick—a gentleman whose skill and taste in the fine arts was undisputed; and whose collections of paintings and memorials of antiquity have rendered the mansion-house of Pennycuick a place of great interest to the curious. By these gentlemen the company and conversation of Dr. Walker was greatly estimated; and a constant intercourse existed between them.

In 1764, the General Assembly, in prosecution of a benevolent design entered into some years before, respecting the religious and moral improvement of the Highlands and Islands of Scotland, appointed Dr. Walker to undertake a mission to these remote parts of the country. This he readily undertook, and performed his arduous task to the entire satisfaction of the Assembly. He was also authorised, by the Commissioners for the Annexed Estates, to inquire into the natural history and productions—the population—agriculture—and the fisheries of the Highlands and Hebrides. In prosecution of these important inquiries, he performed in all six journeys; and, from the mass of useful information collected, a posthumous work, entitled "An Economical History of the Hebrides," was published in 1808.

Not long after his first mission to the Highlands, which tended materially to confirm the high opinion entertained of his character, Dr. Walker was presented by the Earl of Hopetoun to the church of Moffat, in the Presytery of Lochmaben, and county of Dumfries. In this extensive parish a new and inviting field presented itself for exploring the vegetable kingdom of nature ; and it is probable that the frequency of his botanising excursions—the utility or propriety of which were not appreciated by his parishioners—procured for him the title of "the mad minister of Moffat." There was another prominent trait in the demeanour of the Doctor, which no doubt had its due weight in countenancing such an extraordinary soubriquet. This was an extreme degree of nicety in the arrangement of his dress, especially in the adjustment of his hair, which it is said occupied the village tonsor nearly a couple of hours every day.

It is told of the Doctor, that travelling on one occasion from Moffat to the residence of his friend, Sir James Clerk of Pennycuick, he stopped at a country barber's on the way to have his hair dressed. He was personally unknown to Strap, although the latter had often heard of him. The barber did all in his power to give satisfaction to his customer; but in vain he curled and uncurled, according to the Doctor's directions, for nearly three hours. At length, fairly worn out of patience, he exclaimed—"In all my life, I have never heard of a man so difficult to please, except' the mad minister of Moffat.' " This scrupulous attention to his hair he continued to observe until advancing years compelled him to adopt a wig.

The Doctor himself used to mention that he was one day walking in a gentleman's park, where he had been collecting insects, with the handles of an insect net projecting from his pocket. Two ladies were walking near, and he heard one of them say—"No wonder the Doctor has his hair so finely frizzled, for he carries his curling tongs with him."

On the death of Dr. Rarnsay, Professor of Natural History in the University of Edinburgh, in 1778, Dr. Walker made application to the Crown for the vacant chair. In this he was successful, and obtained his commission in 1779. At that period no direct judgment of the General Assembly stood recorded with respect to pluralities, but the parishioners of Moffat were alarmed at the circumstance of their minister's appointment to the Professorship, justly conceiving that, distant as they were from Edinburgh upwards of fifty miles, it was impossible he could properly attend to his pastoral duties. Several meetings of Presbytery were held on the subject, but the Doctor found ways and means to smooth down the opposition ; and he continued for some time to hold both appointments. Owing to the discontent of the people, however, he found his situation extremely irksome and disagreeable. A few years subsequently he was happily rescued from his difficulties by the Earl of Lauderdale, who gave him the church of Colinton, about four miles from Edinburgh; where, from its proximity to the town, he could more easily fulfil the relative duties of his appointments.

Dr. Walker may almost be said to have been the founder of Natural History in the University. His predecessor only occasionally delivered lectures ; and these were never well encouraged, owing no doubt to the little interest generally excited at that time on a subject so important. The want of a proper museum was a radical defect, which the exertions of Dr. Walker were at length in some measure able to rectify. His lectures also proved very attractive, not so much from the eloquence with which they were delivered, as from the vast fund of facts and general information they comprised. Both in the pulpit and in lecturing to his classes, the oratory of Dr. Walker was characterised by a degree of stiffness and formality.

In 1783, when the Royal Society of Edinburgh was formed, the Professor was one of its earliest and most interested members. The opposition offered to the incorporation of the Antiquarian Society, which principally originated in the objections made to the delivery of a course of lectures on the Philosophy of Natural History by the late Mr. Smellie, has already been alluded to in our sketch of that gentleman.

In 1788, Dr. Walker delivered a very excellent course of lectures in the University on agriculture, which is generally supposed to have suggested to Sir William Pulteney the idea of founding a professorship for that important branch of science. In 1792, he published, for the use of his students, "Institutes of Natural History; containing Heads of the Lectures on Natural History delivered in the University of Edinburgh."

Although his talents for literary composition were considerable, it is not known that the Professor ever appeared before the public as the author of any separate work of any extent. With the exception of one or two occasional sermons, and a very curious Treatise on Mineralogy, his contributions were chiefly limited to the various learned societies of which he was a member. For the Statistical Account of Scotland he drew up an account of the parish of Colinton, in a style, and with a degree of accuracy, which fully proved the peculiar talent he possessed for topographical and statistical subjects. He intended at one period to have published a Flora of Scotland, but was anticipated by the Scottish Flora of Lightfoot, Chaplain to the Duchess of Portland, who composed his Flora during his travels in Scotland with Pennant.

Dr. Walker's knowledge of plants was not altogether of a theoretical nature. He made some good experiments on the motion of the sap in trees, which are published in the Transactions of the Royal Society of Edinburgh; and in Lord Woodhonselee's Life of Lord Karnes there are several of the Doctor's letters, which contain judicious remarks on various points of agriculture aud gardening. There are still to be seen some vestiges of his attention to the latter, in the glebe of Moffat, where a few of the less common kinds of trees, such as pinasters and others, planted by him, are still growing.

The garden of the manse at Colinton, which is beautifully situated in a small haugh by the river, was carefully laid off and embellished with a display of indigenous and other hardy plants, which the Doctor delighted to collect and cultivate. But these botanical rarities, like other sublunary things, were fleeting, and destined to take no permanent hold of the soil; for the next incumbent, who was no amateur of botany, but a good judge of the value of land, turned the whole into a potato garden!

Although the Doctor, in his public appearances, was somewhat formal and affected, in private life he was extremely social. He was inclined to society, and had many amusing anecdotes, which he told with much gaiety and good humour. He was greatly addicted to taking snuff. Bailie Creech (afterwards Provost), in his convivial hours, was in the habit of reciting, several of the Professor's stories, at the same time imitating his manner and peculiarities. He was fond of dress, as may be inferred from the Etching, where he is drawn with a nosegay in his hand.

In early life the Doctor was patronised by Lord Bute, and when in London was presented to Rousseau, to accompany him as cicerone. They conversed in Latin, the one not being able to speak the language of the other; and both experienced considerable difficulty in making themselves intelligible.

Dr. Walker died on the 22nd January, 1804, aged upwards of seventy. The latter years of his life were rendered painful by violent inflammation of the eyes, brought on, it is said, by his habit of sitting very late at his studies, and which ended in loss of sight. In addition to this calamity, his wife was attacked with a severe and long illness. She was a sister of Mr. Wauchope of Niddry.