David Gregory (mathematician)

“[T]hose persons seem to apply their thoughts but to a very indifferent purpose in the study of Nature, that overlook this part of Astronomy, from whence the principal and most simple Laws of Nature are to be learn'd.”

“Upon this account it is, that every Problem in the Terrestrial Physics is very operose and perplex'd, on the contrary, in the Celestial Physics, much more easy and simple; tho' even the latter has its difficulties, arising from the different distances and magnitudes of the Celestial Bodies, For the Fix'd Stars are so vastly distant asunder, that they have no mutual action upon each other, observable by us...”

“For the Sun and Planets are separated from one another by so immense a distance, as renders them incapable of exerting most of those forces whereby all Bodies act upon one another; so that they have no other force left them whereby they can affect one another, but the single force of universal Gravity: Whereas in the production of several Phænomena, that are observ'd upon our Earth, innumerable other forces are exerted, such as are very hard to be distinguish'd from one another; which notwithstanding, if not accurately done, in vain do we attempt Nature, and make any inquiry into it.”

“The Celestial Physics, or Physical Astronomy, is not only the first in dignity of all inquiries into Nature... but the first in order, because it is the easiest.”

“[T]hose who are less vers'd in the more abstruse parts of Geometry, or less concerned about the Physical parts, may pass over, and only read the Astronomy separately and distinct...”

“[T]he Physics, it is all taken out of the above mention'd Authors; but is here intermix'd with Astronomy, in such places as seem'd proper and convenient; the Geometry to be met with in it, I have either borrowed elsewhere, and quoted... or delivered it Lemmatrically.”

“My design in publishing this Book, was, that the Celestial Physics, which the most sagacious Kepler had got the scent of, but the Prince of Geometers Sir Isaac Newton, brought to such a pitch as surprises all the World, might, by my... illustrating, become easier to such as are desirous of being acquainted with Philosophy and Astronomy.”

“[F]or the further improvement of natural philosophy a more advanced geometry must be found. ...[T]he reason why physical science has here been brought to a level that is the envy of foreigners is the knowledge... of some more universal geometry. Of what part of this the learned owe to this renowned university and in it to the prince of geometers I shall not speak lest I appear to be fawning, which in a mathematician would be unseemly.”

“The phenomena prove that the tail of a comet is vapour from its head which, when the comet is greatly heated in the neighbourhood of the sun in perihelion, continually rises up and moves away into the regions opposite the sun.”

“Descartes's cosmic system, which he jokingly called his fable of the world, is shown to be a fable indeed.”

“But... Kepler’s problem was to be resolved, to find the position of a body moved in an elliptical orbit at a given time. As concerns an algebraic resolution... adapted to the construction of tables, we... also have produced a work not... to be ashamed of.”

“[W]ith this one problem... three years ago, after the above was published, Gottfried Leibniz... produced a construction... in terms of his system—not without the blemish of paralogism.”

“Since two or more mutually gravitating bodies describe orbits around a common immobile centre of gravity, and since by common consent there is an immense difference between the quantity of matter in the sun and that in the Earth, it is clear that neither the sun nor, much less, the sun in the company of five planets can revolve around an immobile Earth. Thus is shown not only the falsity but the impossibility of the {{w|Tychonic system}}.”

“In the past many very base Remus’s leapt over the walls of the astronomical city, but now the geometers have so fortified it with a ditch and a rampart that the portals of the sun receive those whom impartial Appollonius has loved and whom Kepler, Wren, Wallis and Newton have borne to the aetherial regions, and accordingly the profane, that is ungeometrical men, are exiled and depart from the grove and wander away over the whole heaven.”

“[W]ithin the memory of ourselves and... our fathers, philosophers began to extend the limits of geometry in order to found the kingdom of astronomy. This they have carried out... with such success that now no one can be received into astronomical citizenship who is not a visiting citizen in the most abstruse geometry and has not arisen from the patrician, that is the geometrical, family of philosophers.”

“[I]t is by the help of geometry that all the arts necessary for improving life,.. as geography,.. rules of navigation,.. determining of times... [etc.], have been carried to such an incredible pinnacle of distinction.”

“Although in every age there have been those who cultivated astronomy, either by... observations... or by theories and systems made up according to the state of understanding of any period, or by a talent for exposition, yet the lucubrations of all these astronomers do not reveal the ways of the heaven any more than they reveal the skill and experience of their progenitors in geometrical matters.”

“[T]he easier, simpler and less composite these theories are, the more they will be consonant not only with what has already been observed... but with what is yet to be observed, and with the very machine of the world which was constructed by the supreme creator with the greatest simplicity.”

“It is... most gratifying to my soul that, after spending a large part of my life in other universities, I can be linked in the University of Oxford with the prince of geometers Dr John Wallis as colleague and the most scholarly Dr {{w|Edward Bernard}} as successor.”