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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. |
