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Significant Scots
James Gregory

James GregoryGREGORY, JAMES, whose valuable discoveries served so much to accelerate the progress of the mathematical and physical science in the seventeenth century, was born in 1638, at Drumoak in Aberdeenshire, where his father, the reverend John Gregory, was minister. Little is known of James Gregory’s father, but from some slight notice of him in the Minutes of the General Assembly; and whatever part of the genius of the subject of this memoir was possessed by inheritance seems to have descended from the mother. It is an observation of a distinguished philosopher of the present day, Dr Thomson, that, "he never knew a man of talent whose mother was not a superior woman;" and a more happy instance of the truth of this remark could not be found than that of James Gregory. Mrs Gregory seems to have descended from a family of mathematicians. Her father was Mr David Anderson of Finghaugh, whose brother, Alexander Anderson, was professor of mathematics (about the beginning of the seventeenth century,) in the university of Paris, and he himself was long noted for his application to mathematical and mechanical subjects. The reverend John Gregory died when the subject of this article was yet in his boyhood, and left the care of the education of James to David, an elder brother, and the surviving parent. The mother having observed the expanding powers of his mind, and their tendency to mathematical reasoning, gave these early indications of his genius all possible encouragement, by instructing him herself in the elements of geometry. Having received the rudiments of his classical education at the grammar school of Aberdeen, he completed the usual course of studies at Marischal college. For a considerable time after leaving the university, James Gregory devoted his attention to the science of optics. The celebrated French philosopher Descartes had published his work on Dioptrics the year before Gregory was born, nor had any advances been made in that science until James Gregory published the result of his labours in a work printed at London in 1663, entitled, "Optics Promoted, or the mysteries of reflected and refracted rays demonstrated by the elements of geometry; to which is added, an appendix, exhibiting a solution of some of the most difficult problems in astronomy." In this work, which forms an era in the history of the science of that century which its author so eminently adorned, and which was published when he was only twenty-four, there was first given to the world a description of the reflecting telescope, of which Gregory is the indisputable inventor. He proposed to himself no other advantage from using mirrors instead of glasses in the construction of telescopes, than to correct the error arising from the spherical figure of the lenses, and by forming the reflectors of a parabolic figure, to bring the rays of light into a perfect focus, being ignorant of the far greater error arising from the unequal refrangibility of the rays of light, which it was reserved for Newton afterwards to discover. Gregory went to London a year after the publication of his work on optics, with a view to the construction of his telescope, and was introduced to Mr Rieves, an optical instrument maker, by Mr Collins, secretary to the Royal Society. Rieves could not finish the mirrors on the tool so as to preserve the figure, and so unsuccessful was the trial of the new telescope that the inventor was deterred from making any farther attempts towards its improvement, nor were these reflectors ever mounted in a tube. Sir I. Newton objected to this telescope, that the hole in the centre of the large speculum would be the cause of the loss of so much light, and invented one in which this defect was remedied. The Gregorian form is universally preferred to the Newtonian, when the instrument is of moderate size, the former possessing some material advantages; yet the latter was always employed by Dr Herschel, in those large instruments, by which the field of discovery has, of late, been so much extended. Although the inventor of the reflecting telescope has received all the honour which posterity can bestow, yet it is lamentable to think that he never had the satisfaction of seeing an instrument completed in his own lifetime. It is only necessary to remark farther, on this subject, that some papers of great interest passed between Gregory and Sir Isaac Newton, concerning the reflecting telescope, which may be consulted with advantage by those who would wish to investigate the subject. His work on optics contains, besides the discovery of the reflecting telescope, that of the law of refraction. Descartes had made a similar discovery long ere this, but Gregory had not heard of it till his own work was ready for publication - to which circumstance he alludes in his preface. Playfair, in considering this subject, very justly remarks, that "though the optics of Descartes had been published twenty-five years, Gregory had not heard of the discovery of the law of refraction, and had found it out only by his own efforts;—happy in being able, by the fertility of his genius, to supply the defects of an insulated and remote situation." [Playfair’s Dissertation, in the Supplement to the Encyclopedia Britannica, part 1st, page 25, 6th edition.] The method in which Gregory investigated the law of refraction is truly remarkable, not only for its singular elegance, but originality, and the series of experiments which he instituted for the purpose of demonstration, affords an indelible proof of the accuracy of his observations. It is truly remarkable, that the calculations by this law differ so little from those obtained by the most accurate experiments. There is yet another discovery of the very highest importance to the science of astronomy, which is falsely and, we would hope, unknowingly attributed to another philosopher, whose manifold brilliant discoveries throw an additional lustre over the country which gave him birth. We allude to the employment of the transits of Mercury and Venus, in the determination of the sun’s parallax, the merit of which is always ascribed to Dr Halley, even by that eminent astronomer Laplace. But it is plainly pointed out in the scholium to the 28th proposition of Gregory’s work, published many years prior to Halley’s supposed discovery. The university of Padua was at this time in high repute for mathematical learning, and Gregory repaired thither from London, about the end of 1667, for the purpose of prosecuting his favourite study. Here he published a Latin work on the areas of the circle and hyperbola, determined by an infinitely converging series; a second edition of which he afterwards published at Venice, with an appendix on the transmutation of curves. Mr Collins, who always showed himself zealous in Gregory’s favour, introduced this work to the notice of the Royal Society of London, of which he was secretary. This work received the commendation of that distinguished nobleman lord Brounker, and Dr Wallis, the celebrated inventor of the arithmetic of infinites. Gregory’s attention was once more drawn to the squaring of curves, by the method of converging series, on account of receiving an instance of the case of the circle in a letter from his friend Collins, who informed him that Newton had discovered a general method for all curves, mechanical and geometrical. Gregory speedily returned to Collins a method for the same purpose, which he was advised by his brother David to publish. Gregory refused to do this, and that from the most honourable motive: as Newton was the original inventor, he deemed it unfair to publish it, until Sir Isaac should give his method to the public. Soon after, he returned to London, and from his celebrity as a mathematician, he was chosen a fellow of the Royal Society. He read before the society, the account of a dispute in Italy concerning the motion of the earth, which Riciolli and his followers had denied, besides many other valuable communications. Huygens had attacked Gregory’s method of quadrature in a journal of that period, to which he replied in the Philosophical Transactions. The dispute was carried on with great warmth by both, and from Gregory’s defence it would appear he was a man of warm temperament, but acute and penetrating genius. Of the merits of either, in this dispute, it would be out of place here to enter into detail. Leibnitz, who considered the subject with attention, and whose capacity of discernment in such matters cannot be questioned, is of opinion, that although Huygens did not point out errors in the work of Gregory, yet he obtained some of the results by a much simpler method.

The small work "Exercitationes Geometricae," published by Gregory at London in 1668, consisted of twenty-six pages, containing however a good deal of important matter. Nowhere do we learn more of the real private character of Gregory than in the preface and appendix to this little work. He speaks in explicit terms of his dispute with Huygens, complains of the injustice done him by that philosopher and some others of his contemporaries; and we are led to conclude from them, that he was a man who, from a consciousness of his own powers, was jealous of either a rival or improver of any invention or discovery with which he was connected. The same year in which he published this last work, he was chosen professor of mathematics in the university of St Andrews. The year following he married Miss Mary Jamieson, daughter of Mr George Jamieson, the painter whom Walpole has designated the Vandyke of Scotland. By his wife he had a son and two daughters. The son, James, was grandfather of Dr Gregory, author of the "Theoretiem Medicinae," and professor of the theory of medicine in the university of Edinburgh. James Gregory remained at St Andrews for six years, when he was called to fill the mathematical chair in the university of Edinburgh. During his residence at St Andrews, he wrote a satire on a work of Mr George Sinclair’s, formerly professor of natural philosophy in Glasgow, but who had been dismissed on account of some political heresies. Dr Gregory did not live to enjoy the chair in Edinburgh more than one year; for returning home late one evening in October, 1675, after showing some of his students the satellites of Jupiter, he was suddenly struck blind, and three days afterwards expired. Thus, at the early age of thirty-seven, in the vigour of manhood, was put a melancholy termination to the life of James Gregory. Of the character of this great man little can be said. His knowledge of mathematical and physical science was very extensive; acuteness of discrimination and originality of thought are conspicuous to all his works; and he seems to have possessed a considerable degree of independence and warmth of temper.

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