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Newtonian Astronomy

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Newtonian Astronomy

‘Read carefully the definitions, laws, and first three sections (that is, the first 17 propositions) of Book 1, then pass to Book III ‘De mundi systemate’ consulting the propositions there cited from the earlier books as the reading may require.’

Newton, Principia (London, 1687).*


Sir Isaac Newton, Philosophiae naturalis principia mathematica (Cambridge, 1713), title page.

Edward Worth bought not one but two editions of Sir Isaac Newton’s celebrated Principia in which Newton announced the law of universal gravitation, a law which ever since has formed the basis of our understanding of the solar system. The above illustration is the title page of his second edition of the work, while the following portrait of Newton is taken from Worth’s third edition of 1726. We can see where Worth has added in the date of Newton’s death:


Sir Isaac Newton, Philosophiae naturalis principia mathematica (London, 1726, vol 1, frontispiece portrait.

That Newton was a seminal influence on Worth entire collection is readily apparent. He bought a number of his works (including two editions of his Arithmetica universalis and both an English and Latin edition of the Opticks) and was likewise interested in collecting texts by commentators on Newton, such as Desaguliers, Gregory and Whiston.

Indeed Worth’s fascination for Newtonian works may also help explain the rather large collection of works by Kepler in the Worth Library since Newton was seen to build on Kepler’s three laws. Not, of course, that Newton himself saw it quite that way. As Wilson points out (1989), Newton considered that that he himself was the first to prove the ellipse – Kepler, in his view, had led the way by guessing that orbits to be elliptical. Kepler’s Law was, in the words of Newton in Phenomenon V ‘Propositio est Astronomis notissima…’ a well-known proposition, well-known but not proven. In fact he appears only to have accepted Kepler’s third rule (elucidated in Worth’s copy of Kepler’s Harmonices Mundi (Linz, 1619)).

That Newton wasn’t alone in his view may be seen in the work of other authors collected by Worth: the French astronomer Ismaël Boulliau (Bullialdus) whose work is investigated in the section on Copernicus in this website, and the Italian astronomer Giambattista Riccioli.

Dating Newton’s theory of universal gravitation has been a scholarly challenge for centuries. The Newtonian school, exemplified by William Whiston, argued that the initial idea first came to him as early as 1665/6 and that his ‘Moon test’ of that period was an attempt at confirmation. Robert Hooke dated it much later – to his and Newton’s epistolary correspondence near the end of 1679, effectively arguing that Newton had robbed the idea from him. Yet other scholars such as Wilson (1989) and (2003) have argued for a later date – no earlier than the summer of 1684 when Newton produced his tract De Motu. Wilson’s analysis of Newton’s Hypothesis explaining ye properties of light (1675) and his letter to Robert Boyle of 28 February 1679 demonstrate that Newton had not as yet formulated the theory at the stage of writing those two documents. He further suggests that Newton’s heightened interest in the comet of 1680/1 was a sign that he was thinking about ways to prove his theory. Clearly his work on the 1680/1 comet was central: as Whiston points out, Newton’s work on it helped him to prove beyond doubt that Kepler was correct:

‘At length came that prodigious Comet of the Year 1680; which descending (as it were from an infinite Distance) perpendicularly towards the Sun, arose from him again with as great a Velocity.

This Comet, (which was seen for four Months continually) by the very remarkable and peculiar Curvity of its Orb (above all others) gave the fittest Occasion for investigating the Theory of its Motion. And the Royal Observatories at Paris and Greenwich having been for some time founded, and committed to the Care of most excellent Astronomers, the apparent Motion of this Comet was most accurately (perhaps as far as humane Skill cou’d go) observ’d by Mrs. Cassini and Flamsteed.

Not long after, that great Geometrician the Illustrious Newton, writing his Mathematical Principles of Natural Philosophy, demonstrated not only that what Kepler had found, did necessarily obtain in the Planetary System; but also, that all the Phaenomena of Comets wou’d naturally follow from the same Principles; which he abundantly illustrated by the Example of the aforesaid Comet of the Year 1680; shewing at the same time, a method of delineating the Orbits of Comets Geometrically; therein solving (not without meriting the highest Admiration of all Men) a Problem, whose Intricacy render’d it scarce Accessible to any but himself. This Comet he prov’d to move round the Sun in a Parabolical Orb, and to describe Area’s (taken at the Center of the Sun) proportional to the Times.’

William Whiston, Sir Isaac Newton’s mathematick philosophy more easily demonstrated: with Dr. Halley’s account of comets illustrated. Being forty lectures read in the publick schools at Cambridge (London, 1716), p. 412-3.

As Wilson argues (1989), Newton was interested in the 1680/1 comet because he realised that if he could prove that comets were subject to the same gravitational forces as planets then gravitation must be a universal phenomenon. His conclusions in 1681 were negative (mainly because he, like Cassini and Huygens, judged that the comet seen in November 1680 in the morning sky and on 10 December in the evening sky, were two separate comets). It was not until December 1684 in the third draft of his De Motu corporum in gyrum (On the Motion of bodies in an orbit), which in effect was an early draft of many of the propositions in the Principia, that he began to be more optimistic about the theory, an optimism that was strengthened by his realisation in June 1686 that the November 1680 comet and the December-March 1680/1 had been one and the same.

Newton’s interest in the comet post-dates his famous 1679 correspondence with Robert Hooke. However much Newton might deny the latter’s role, Hooke certainly deserves some credit. However, though Hooke was the first to propose the idea of a general attraction towards the centre he did not conceive of it in universal terms and, as Westfall states (2004), ‘the central theme of the Principia would be the quantitative exploration of the new concept, something Hooke had not achieved’. Worth himself obviously felt that Hooke had much to offer as he not only collected his Micrographia (London, 1667) but also Hooke’s The posthumous works: containing his Cutlerian lectures and other discourses, read at the meetings of the illustrious Royal Society … to these discourses is prefixt the author’s life giving an account of his studies and employments, with an enumeration of the many experiments, instruments, contrivances and inventions, by him made and produc’d as curator of experiments to the Royal Society publish’d by Richard Waller (London, 1705):

Robert Hooke, The Posthumous Works (London, 1705), title page.

Newton’s Opticks

Sir Isaac Newton, Opticks (London, 1704), title page.

Among the works by Newton bought by Worth was the 1704 edition of the Opticks (and, indeed the 1706 Latin translation). Here we see how Newton’s telescope which effectively halved the length of the Keplerian telescope:


Sir Isaac Newton, Opticks (London, 1704), Diagram of the Newtonian telescope, Fig 29.

In the following two illustrations we see Newton’s explanation of how a telescope could be shortened:

Newtonian6 Newtonian7
Sir Isaac Newton, Opticks (London, 1704), p. 79
Sir Isaac Newton, Opticks (London, 1704), p.

The Reception of Newtonian Astronomy

Edward Worth did not just collect different editions of works by Newton himself – he also displayed considerable interest in those authors responsible for the reception of Newtonian astronomy. Undoubtedly one reason for this was his membership of the Royal Society for many of the authors were fellow members, but it is likely also that, with nearly everybody else on the planet, Worth needed some introductory text to the Principia and since Newton himself had refused to provide one, Worth had to look elsewhere. He collected works by three of the principle commentators on Newton’s works: John Theophilus Desaguliers, David Gregory and William Whiston whose lives and works display the often complex diffusion patterns of the Principia.

John Theophilus Desaguliers, 1683-1744, had come to England at the age of two with his Huguenot refugee family. Studying at Oxford under the tutelage of John Keill, one of the leading exponents of Newtonian philosophy, Desaguliers quickly became a staunch follower of Newton. This tie was strengthened when, with Newton’s assistance, he was given the post of experimenter for the Royal Society. Desaguliers quickly made a name for himself as one of the many public experimental lecturers in London. As reward for his work he was elected a Fellow of the Royal Society in 1714 and some five years later published the book collected by Worth: A system of experimental philosophy, prov’d by mechanicks… To which is added… a Machine representing the Motion of the Moon about the Earth; Venus and Mercury about the Sun, according to the Copernican System (London, 1719).

The publishing history of this work is a demonstration of the unscrupulous and often cut-throat state of the Newtonian publishing industry at the time. The origins of the book were Desaguliers lectures at the Censorium in 1718. The founder of the Censorium theatre, Richard Steele, asked Desaguliers to undertake the tuition of a friend of his, Paul Dawson, in experimental mechanics and suggested that Dawson might learn faster if he had a set of lecture notes to hand. Desaguliers, generously if unwisely, agreed, only to find that Dawson prepared an edition of the lecture notes and published them with the London publishers William Mears in 1719 – without Desagulier’s permission. As Wigelsworth (2003) suggests, this was a serious blow to Desaguliers on two fronts: first, he lost the payment he might have received from the publisher for the text itself; secondly, and more dangerously, an un-corrected edition of experiments was detrimental to his continuing position as a public experimenter. Desaguliers earned his living by publicly presenting experiments. If a text existed which undermined that living it could have serious financial repercussions. It was definitely not a case of all publicity is good publicity. Desaguliers was aware that some publicity could be very costly indeed. It was precisely for that reason that he agreed with the publishers that, in exchange for a small sum of money, he would correct the text and the corrections be included as errata. Desaguliers’ disquiet is clearly visible in his note on these errata: he assured the reader that he had ‘looked over the whole book, and corrected every error therein; because I was unwilling that those who buy it should find it any wise imperfect, and desirous that it might be of use to such as go thro’ Courses of Experimental Philosophy. The Reader therefore is desired to Correct the Faults with his Pen, as the Errata direct, before he begins to read the Lectures.’ Unfortunately this was not the end of Desaguliers’ vicissitudes with the London printing trade – in the same year his translation of the Mathematic Elements of Natural Philosophy by the Dutch Newtonian, Willem Jacob ‘sGravesande, was effectively over-shadowed by another English translation of the same work being brought out at the same time by Mears. This latter book, not collected by Worth, is perhaps the key to Desaguliers success as an exponent of the Newtonian system: he was able to not only translate the works of continental Newtonians but also produce translations and French editions of his own works which could then spread the Newtonian philosophy abroad.

In the following illustrations we see Desagulier’s description of ‘Rowley’s Horary’, in A system of experimental philosophy, prov’d by mechanicks (London, 1719), pp. 194-6.



John Theophilus Desaguliers, 
A system of experimental philosophy, prov’d by mechanicks 
(London, 1719), pp. 184-5.

David Gregory, 1659-1708, the Savilian Professor of Astronomy at Oxford, was in a considerably more secure social position. Gregory was as committed a Newtonian as Desaguliers and received with delight his copy of the Principia. Though he was lecturing at the University of Edinburgh at the time he did not, however, seek to introduce it into the syllabus, fearing no doubt that its complicated nature might prove too difficult for his students, though he clearly instructed some students to write their theses on various aspects of Newtonian philosophy.

In December 1691, after a hard-fought race, Gregory was elected as Savilian Professor of Astronomy at Oxford. In his inaugural address which he delivered on 21 April 1692 he outlined his pedagogical plan, one which centred on the works of Kepler and, above all as the following extract relates, the works of Newton:

‘For the excellent geometer Mr. Isaac Newton in addition to the geometric figure in any orbit of a projectile sought also to find the measure of the centripetal force (tending to a given centre) of the body borne in that orbit, from whatever cause that force may arise, be it from a deeper mechanical one or from a law imposed by the supreme creator of all things. He inquires geometrically into the law of centripetal force of a body moved in the circumference of a circle with the force tending to a given point either on the circumverence or anywhere outside it or inside it, or even infinitely removed. Bt the same method he seeks the law of centripetal force tending to the centre of a plane nautical spiral (that is one that the radii cut in a given angle) which will drive a body in that spiral. Also the law of centripetal force that would make a body rotate in an ellipse when the centre of the ellipse coincides with the centre of forces. If the ellipse is changed into a hyperbola and the centripetal force into a centrifugal one the same things apply to the hyperbola. Also the resolution of the same problem when the centre of forces coincides with either focus of the ellipse shows that the law of centripetal force is reciprocally in the duplicate ratio of the distance <i.e. the inverse square of the distance>; others had long before shown that this was the one and only law that would satisfy the other phenomenon observed by Kepler in the motion of the planets. These results also apply to the hyperbola and the parabola when the centre of forces is situated in a focus of the conic section.’*

Gregory became a Fellow of the Royal Society in the same year. He was the author of a host of works but undoubtedly the most important was the text collected by Worth, Gregory’s Astronomiae physicae & geometricae elementa (Oxford, 1702).


David Gregory, Astronomiae physicae & geometricae elementa (Oxford, 1702), title page.

As Guerrini points out (2004), this was ‘the first textbook on astronomy to integrate Newton’s gravitational theory with standard findings’. Newton’s decision to include the first publication of his lunar theory as part of the work not only gave it added appeal but also demonstrates the close ties between the two scientists.

The career of last of the triumvirate, William Whiston, 1667-1752, mirrors aspects of both Desaguliers’s and Gregory’s. Whiston had been educated at Cambridge where he took holy orders. Encouraged by a paper of David Gregory’s to re-read the Principia he became an ardent Newtonian, publishing a host of works from 1696 onwards. The work depicted here is Worth’s copy of Whiston’s Astronomical lectures, read in the publick schools at Cambridge, (London, 1715).


William Whiston, Astronomical lectures, read in the publick schools at Cambridge (London, 1715), title page.

As the title page makes clear, the text also incorporates astronomical tables by authors consistently neglected by Worth: Flamsteed, Halley, Cassini and Street.

The lectures were those Whiston had given following his succession as third Lucasian Professor of Mathematics in 1702. The work had originally appeared in Latin under the title Praelectiones astronomicae in the year 1707, when Whiston was still Lucasian professor (he held the position until 1710). This work, along with his Sir Isaac Newton’s mathematick philosophy more easily demonstrated: with Dr. Halley’s account of comets illustrated. Being forty lectures read in the publick schools at Cambridge (London, 1716), a text also collected by Worth, provided introductory texts to Newtonian astronomy and proved to be immensely popular with undergraduate students for whom they had originally been written in an attempt to simplify the Newtonian system. Largely because of them Whiston received acclaim as a leading exponent of Newtonian astronomy. His participation in a series of lectures on the experimental philosophy at Cambridge added to this fame.

Whiston’s brief but fruitful sojourn as Lucasian professor came to an abrupt end in 1710 when he was expelled from the university on the charge of heresy. In the previous year he had unwisely published a work advocating anti-trinitarian theology and retribution was swift. Whiston had no choice but to move to London and set up as one of the many experimental lecturers in the city. His decision to align forces with Francis Hauksbee the younger led to the pair setting up a successful experimental lecture course and his income was further increased in 1727 when a royal annuity was granted him. In 1717 he produced a work which combined his two intellectual loves: Astronomical principles of religion, natural and reveal’d (London, 1717) – a work again collected by Worth.

Worth’s library was very much a Newtonian library, reflecting as it does his membership of the Royal Society, but it is clear that the inclusion of one work of Newtonianism in the library was not collected by him: Bryan Robinson’s Dissertation on the aether of Isaac Newton (Dublin, 1743), a work published ten years after Edward Worth’s death in 1733.

Bryan Robinson, Dissertation on the aether of Isaac Newton (Dublin, 1743), title page.

The inclusion of this work on Newtonian physiology is not a mystery. Bryan Robinson, 1680-1754, was a friend of Worth’s and a fellow Trustee of Dr. Steevens’s Hospital where the Edward Worth Library remains to this day. Robinson was a prominent member of early eighteenth-century Dublin’s medical establishment: he had been appointed regius professor of physic at Trinity College, Dublin in 1745 and he was elected president of the Royal College of Surgeons no less than three times. He was also a committed Newtonian, not only writing on the ether but also attempting to introduce Newtonian concepts in his Treatise of Animal Oeconomy (1732-33), a work which is also in the Worth Library. His work sheds important light on the spread of the Newtonian philosophy in Dublin at this time. In the following illustration, taken from his Dissertation on the aether of Isaac Newton we see his explanation of a table on the distances of the planets and his explanation of it: Newtonian13Newtonian14

Bryan Robinson, Dissertation on the aether of Isaac Newton (Dublin, 1743), pp. 46 and 45.

Selected Reading

*[translation by Wilson (2003)].
Cohen, I. B. (1993). ‘Newton’s description of the Reflecting Telescope’, Notes and Records of the Royal Society of London, 47, no. 1, 1-9.
Eagles, C. M. (1977). ‘David Gregory and Newtonian Science’, The British Journal for the History of Science, 10, no. 3, 216-225.
Fara, P. (20040). ‘Desaguliers, John Theophilus (1683–1744)’, Oxford Dictionary of National Biography.
Feingold, M. (2004). The Newtonian Moment. Isaac Newton and the Making of Modern Culture. Oxford and New York: Oxford University Press.
Guerrini, A. (2004). ‘Gregory, David (1659–1708)’, Oxford Dictionary of National Biography.
*Lawrence, P. D. and Molland, A. G. (1970). ‘David Gregory’s Inaugural Lecture at Oxford’, Notes and Records of the Royal Society of London, 25, no. 2, 143-178.
Norgate, G. L. G. (2004). ‘Robinson, Bryan (1680-1754), physician and author’, Oxford Dictionary of National Biography.
Pugliese, P. J. (2004). ‘Hooke, Robert (1635-1703), natural philosopher’, Oxford Dictionary of National Biography.
Snobelen, S. D. (2004). ‘Whiston, William (1667-1752), natural philosopher and theologian, Oxford Dictionary of National Biography.
Wigelsworth, J. R. (2003). ‘Competing to Popularise Newtonian Philosophy: John Theophilus Desaguliers and the Preservation of Reputation’, Isis, 94, no. 3, 435-455.
Westfall, R. S. (2004). ‘Newton, Sir Isaac (1642–1727)’, Oxford Dictionary of National Biography.
Wilson, C. (1989). ‘Astronomy from Kepler to Newton. Historical Studies. London: Variorum.
Wilson, C. (2003). ‘The Newtonian achievement in astronomy’ in R. Taton and C. Wilson (eds). Planetary Astronomy from the Renaissance to the rise of astrophysics. Part A: Tycho Brahe to Newton. Cambridge: Cambridge University Press. The General History of Astronomy Series.
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