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Significant Scots
David Gregory

GREGORY, DAVID, the able commentator on Newton’s Principia, and Savilian professor of astronomy at Oxford, was born at Aberdeen on the 24th of June, 1661. His father, Mr David Gregory, brother of the inventor of the reflecting telescope, had been educated as a merchant, and spent a considerable time in Holland; but by the death of his elder brother he became heir to the estate of Kinnairdie, and from a predilection for the mathematics and experimental philosophy, he soon afterwards renounced all commercial employments, devoting himself entirely to the cultivation of science. The peculiarity of Mr Gregory’s pursuits, caused him to be noted through the whole country, and he being the first person in Scotland who possessed a barometer, from which he derived an extensive knowledge of the weather, it was universally believed that he held intercourse with the beings of another world. So extensive had this belief been circulated, that a deputation from the presbytery waited on him, and it was only one fortunate circumstance that prevented him from undergoing a formal trial for witchcraft. He had from choice obtained an extensive knowledge of the healing art, his opinion was held in the highest estimation, and as he practiced in all cases without fee, he was of great use in the district where he lived. It was this circumstance alone that prevented the reverend members of the presbytery from calling him to account for his superior intelligence. His son David, the subject of this sketch, studied for a considerable time at Aberdeen, but completed his education at Edinburgh. In 1684, when he was only twenty-three years of age, he made his first appearance as an author, in a Latin work concerning the dimensions of figures, printed in Edinburgh, and entitled, "Exercitationes Geometricae." The same year in which this work was published, he was called to the mathematical chair in Edinburgh college, which he held with the greatest honour for seven years. Here he delivered some lectures on optics, which formed the substance of a work on that science, of acknowledged excellence. Here also Gregory had first been convinced of the infinite superiority of Newton’s philosophy, and was the first who dared openly to teach the doctrines of the Principia, in a public seminary. This circumstance will ever attach honour to the name of Gregory; for let it be remembered, that in those days this was a daring innovation; and Cambridge university, in which Newton had been educated, was the very last in the kingdom to admit the truth of what is now regarded by all as the true system of the world. Whiston, in his Memoirs of his Own Time, bewails this in "the very anguish of his heart," calling those at Oxford and Cambridge poor wretches, when compared with those at the Scottish universities. In the year 1691 Gregory went to London, as there had been circulated a report that Dr Edmond Bernard, Savilian professor at Oxford, was about to resign, which formed a very desirable opening for the young mathematician. On his arrival in London he was kindly received by Newton, who had formed a very high opinion of him, as we learn from a letter written by Sir Isaac to Mr Flamstead, the astronomer royal. Newton had intended to make Flamstead a visit at Greenwich observatory, with a view to introduce Gregory, but was prevented by indisposition, and sent a letter with Gregory by way of introduction. "The bearer hereof is Mr Gregory, mathematical professor at Edinburgh college, Scotland. I intended to have given you a visit along with him, but cannot; you will find him a very ingenious person, a good mathematician, worthy of your acquaintance." Gregory could not fail to be highly gratified by the friendship of two of the greatest men of the age, and most particularly eminent in that department of science, which he cultivated with so much zeal and success. Such a mind as Newton’s was not likely to form an opinion of any individual, on a vague conjecture of their ability, and the opinion once established would not be liable to change; accordingly we find that his attachment to the interests of the young mathematician, were only terminated by death. In a letter addressed a considerable time afterwards to the same amiable individual, he writes thus, "But I had rather have them (talking of Flamstead’s observations upon Saturn, for five years, which Newton wished from him) for the next twelve or fifteen years—if you and I live not long enough, Mr Gregory and Mr Halley are young men."

Gregory’s visit to London was important to his future fame as a mathematician. He was elected a fellow of the Royal Society, and afterwards contributed many valuable papers to their transactions. At the head of these must be mentioned that which he delivered on his first introduction to their meetings, a solution of the famous Florentine problem, which had been sent as a challenge to the British mathematicians. Gregory’s solution, which is extremely beautiful, will be found in the number of the Philosophical Transactions for January, 1694. On the 8th of February, 1692, David Gregory was made master of arts, of Baliol college, Oxford; and on the eighteenth of the same month he received the degree of doctor of physic. At this time he stood candidate with Dr Halley for the Savilian professorship of astronomy at Oxford. Gregory had a formidable rival to contend with, as great interest was used for Halley at court, and he had besides rendered himself eminent by his numerous and important discoveries. Gregory in all likelihood would not have obtained this situation, notwithstanding the zealous intercession of Newton and Flamstead, had it not been for a circumstance which is stated by Whiston in his Memoirs of his Own Time, as follows: "Halley being thought of as successor to the mathematical chair at Oxford, bishop Stillingfleet was desired to recommend him at court; but hearing that he was a sceptic and a contemner of religion, the bishop scrupled to be concerned till his chaplain Mr Bentley should tally with him about it; which he did, but Halley was so sincere in his infidelity, that he would not so much as pretend to believe the Christian religion, though he was likely to lose a professorship by it—which he did, and it was given to Dr Gregory." To the honour of science let it be mentioned, that this circumstance, which opposed the interest of these two mathematicians so directly to each other, instead of becoming the cause of those petty jealousies or animosities, which in such cases, so commonly occur, was in the present instance the foundation on which was raised a firm and lasting friendship. Nor is it perhaps too bold to suspect, that the liberality displayed in this instance by these two eminent men, proceeded not so much from themselves as from the science which they cultivated in common. The scruples of Stillingfleet in time lost their efficacy, and Gregory had soon after the pleasure of having Dr Halley as his colleague, he having succeeded Dr Wallis in the Savilian chair of Geometry.

In 1695, he published at Oxford a very valuable work on the reflection and refraction of spherical surfaces. This work is valuable as it contains the first hint for a practical method of improving the refracting telescope and destroying the chromatic defect of these instruments. The difficulty to be avoided in those telescopes which operate by glasses instead of mirrors, lies in procuring a large field of view, and at the same time retaining distinctness of vision. Gregory drew an analogy from the construction of the eye, and by referring to the method by which this was effected in nature, gave the hint that the same principle might be applied in practice. This, perhaps, paved the way for the achromatic glasses, one of the finest triumphs of modern science. A simplicity pervades the whole work truly characteristic of the author’s mind. But the work on which the fame of David Gregory must ultimately depend, was published in 1702, entitled "Elements of Physical and Geometrical Astronomy." This work was a sort of digest of Newton’s Principia. Great originality was shown in the illustrations, and the arrangement was so adapted as to show the progress the science had made in its various gradations towards perfection; and it was allowed by Newton himself that Gregory’s work was an excellent view of his system.

Sir Henry Savile had projected a design of printing a uniform series of the ancient mathematicians; in pursuance of which Gregory published an edition of Euclid, and in conjunction with Dr Halley, he commenced the Conics of Appollonius; but scarcely had he entered upon this interesting undertaking, when death put a period to his existence. He departed this life in 1701, at Maidenhead in Berkshire, where it is believed his body is interred. His wife erected a monument at Oxford to his memory, with a very simple and elegant inscription. Of the talents of Dr Gregory ample testimony is borne by the works which he bequeathed to posterity, and of his worth as a private individual by the respect in which he was held by his contemporaries, Flamstead, Keil, Halley, and above all, Sir Isaac Newton, who held him in the highest estimation. Of Newton’s respect for him we shall add one other instance: Sir Isaac had intrusted Gregory with a copy of his Principia in manuscript, on which Gregory wrote commentary; of the benefit of which the great author availed himself in the second edition. Dr John Gregory presented a manuscript copy of this to the university of Edinburgh, in the library of which it is carefully preserved. Of his posthumous works, two deserve particularly to be noticed; one on practical geometry, published by Mr Colin Maclaurin, and a small treatise on the nature and arithmetic of Logarithms, subjoined to Keil’s Euclid, which contains a simple and comprehensive view of the subject.

An anecdote is told of David Gregory of Kinnairdie, Dr Gregory’s father, which it would not perhaps, be altogether proper to omit. He had, as was remarked at the beginning, a turn for mathematical and mechanical subjects, and during queen Anne’s wars had contrived a method to increase the effect of field ordnance. He sent it to the Savilian professor, his son, wishing his opinion, together with Sir I. Newton’s. Gregory showed it to Newton, who advised him earnestly to destroy it, as said Newton, "Any invention of that kind, if it even were effectual, would soon become known to the enemy, so that it would only increase the horrors of war." There is every reason to think that the professor followed Newton’s advice, as the machine was never afterwards to be found.

It is a more singular circumstance, and indeed without parallel in the scientific history of Scotland, that this old gentleman lived to see three of his sons professors at the same time, viz. David, the subject of the preceding sketch; James, who succeeded his brother in the chair of mathematics at Edinburgh; and Charles, professor of mathematics in the university of St Andrews.

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