From times immemorial, astrology has been a determining factor in the decisions and actions of men of all ranks and stations. At the begin of the 17th century, great scientists as Tycho Brahe, Galileo Galilei, Johannes Kepler and Pierre Gassendi now best remembered for their roles in the development of modern physics and astronomy all held astrology in high esteem.
However, at the end of the 17th century, the scientific community had completely turned away from astrology. For some the subject of derision, others preferred to ignore it completely so, hardly a single word on astrology, either pro or contra, is to be found in the works of scientists as Christiaan Huygens (1629-1695) or Isaac Newton (1642-1727).
However, in the case of Newton, the astrological literature presents a different view and even claims that Newton was in secret an ardent student of astrology. As evidence the following anecdote is often quoted: when the astronomer Edmond Halley (1656-1742), of comet fame, once spoke depreciatively on the subject of astrology, Newton is said to have berated him with the remark: “Sir Halley, I have studied the matter, you have not!”
How much value may we store in such a testimony? The first questions that should be answered are: what is the source for this statement and what evidence is there that Newton ever “studied the matter”.
During the past few decades, an enormous amount of studies have been published on Newton, reaching a high-water mark during the tercentenary of the publication of Newton’s Philosophiæ naturalis principia mathematica (1687). Many of his hitherto unpublished papers, notably those from the so-called ‘Portsmouth Collection’, have been edited and commented on.
However, none of these studies have turned up one shred of evidence that Newton ever conducted any research on astrology. One of the foremost Newton scholars, the English historian of science Derek Thomas Whiteside has stated that he never found any reference to astrology among the 50 million words which have been preserved from Newton’s hand.
Moreover, the claim that the Bodleian Library at Oxford possesses a rare treatise on astrology written by Newton has also proven to be completely unfounded.
Corroborative evidence on how minimal Newton’s interests on astrology really were can be found by inspecting the inventory of the books from his library that was made up after his death. This inventory has been preserved and in many cases even the books themselves, with Newton’s own comments and annotations, have been traced to various major libraries.
Among the 1752 books with identifiable titles on this list, no less than 477 (27.2%) were on the subject of theology, 169 (9.6%) on alchemy, 126 (7.2%) on mathematics, 52 (3.0%) on physics and only 33 (1.9%) on astronomy. Surprisingly, Newton’s books on the disciplines on which his scientific fame rests amount to no more than 12% of his library.
At his death, Newton’s library possessed no more than four books on the subject of astrology: a work by the German astrologer Johann Essler from Mainz (end 15th/begin 16th century), a treatise on palmistry and astrology by the English doctor/astrologer Richard Saunders (1613-1675), an almanac from the same using the pseudonym Cardanus Rider and finally a work debunking astrology by the philosopher-poet and Cambridge professor Henry More (1614-1687).
Ironically, Saunder’s book on palmistry and astrology may even have been the incentive to Newton’s scientific career. On August 31, 1726, shortly before his death, Newton was interviewed by his nephew John Conduitt (1688-1737), who was collecting biographical material on his illustrious uncle.
During this interview, Newton confided to Conduitt that his interest in science had first been roused in the summer of 1663, when, as a young student at Cambridge, he purchased a book on astrology at the midsummer fair at Stourbridge. Baffled by the incomprehensible astrological diagrams and calculations in this work he then studied some books on geometry and calculus (such as by Euclid, Frans van Schooten and René Descartes) and was “soon convinced of the vanity & emptiness of the pretended science of Judicial astrology”.
Conduitt’s notes are also corroborated by another memorandum that was drawn up shortly after Newton’s death by his friend Abraham de Moivre (1667-1754) and which was also consulted by Conduitt. Although the Newton biographer Louis Trenchard More expressed his reservations against the trustworthiness of an anecdote recorded more than 60 years after the event, it is cited as completely reliable in the more authoritative Newton biographies by David Brewster and Richard Samuel Westfall.
The studies into Newton’s unpublished papers mentioned above have revealed that during the greater part of his scientific career, his secret passions in fact lay in alchemy and matters of theology (such as the nature of the Holy Trinity, the dimensions of Solomon’s Temple, biblical prophecies and biblical chronology).
It will therefore not come as a surprise that the true source for our anecdote in fact derives from Newton’s latter interests. More than 50 years ago the American historian of science I. Bernard Cohen was able to trace it back to the highly regarded Newton biographies by the English physicist David Brewster (1781-1868) in which it is cited in full as:
‘... when Dr. Halley ventured to say anything disrespectful to religion, he invariably checked him, with the remark, “I have studied these things – you have not”.’
The fact that Halley and Newton often quarreled on theological matters is confirmed by another remark recorded by John Conduitt, who in turn heard it from his wife (and Newton’s niece) Catherine Conduitt (née Barton; 1679-1739). However, these altercations were never so intense as to cause a rift between these two great scientists.
 This webpage is based on an article that was first published in Correlation: Journal of Research into Astrology, 12 (1993), nr. 1, 33-37, and is in turn an expanded version of a short note first published in 1992 in Skepter, the journal of the Dutch Skeptics.
 In his posthumously published Cosmotheoros, Huygens declares “And as for the Judicial Astrology, that pretends to foretell what is to come, it is such a ridiculous, and oftentimes mischievous Folly, that I do not think it fit to be so much as named”; cf. Oeuvres Complètes de Christiaan Huygens publiées par la Société Hollandaise des Sciences (The Hague: Martinus Nijhoff, 1944), vol. 21, pp. 736-737 [p. 68 in the English translation of 1698]. In 1659, when Huygens had been asked by princess Albertina-Agnes, the daughter of the Dutch stadtholder Frederik Hendrik, to draw up her horoscope, he professed complete ignorance and even disbelief of the subject. In order to comply with the royal command, he had no other option but to persuade his French correspondent Ismael Boulliaud (1605-1694) in Paris to provide the requested horoscope, which was duly delivered in the following year; cf. Oeuvres Complètes ..., vol. 2, pp. 523-525 & 530 [Letters 692 & 696], vol. 3, pp. 3-5, 7-10, 12-14, 16-17, 19, 21-23, 25-26, 29-34 & 49-51 [Letters 704, 706-708, 711, 714, 716, 718-719, 721, 723-724 & 733] and vol. 22, pp. 505-506.
 Cf. M. Gauquelin, The Cosmic Clocks: From Astrology to a Modern Science (London: Peter Owen, 1969), p. 49; D. Parker & J. Parker, A History of Astrology (London: André Deutsch Ltd., 1983), p. 159; J.A. West, The Case for Astrology (Harmondsworth: Penguin Books Ltd., 1991), 2nd ed., pp. 115-116.
 S.J. Tester, A History of Western Astrology (Woodbridge: The Boydell Press, 1987), pp. 229-230; P. Curry, Prophecy and Power: Astrology in Early Modern England (Cambridge: Polity Press, 1989), pp. 142-144.
 T.G. Cowling, Isaac Newton and Astrology (Leeds: Leeds University Press, 1977), p. 3.
 R. Eisler, The Royal Art of Astrology (London: Herbert Joseph Ltd., 1946), pp. 239-241.
 J. Harrison, The Library of Isaac Newton (Cambridge: Cambridge University Press, 1978), cf. pp. 58-78.
 Ioannis Essler Maguntinus, Tractatus utilis ante LX annos conscriptus, cui titulum fecit, Speculum astrologorum ... (Basel, 1596; first published in 1508); bound in one volume with Georg Peurbach, Theoricæ novæ planetarum. Newton’s personal copy, which is presently kept at the Trinity College Library at Cambridge, displays no dog-ears, marginal notes, or other evident signs of regular use.
 R. Saunders, Palmistry, the secrets thereof disclosed; or, a familiar, easy and new method, whereby to judge of the most general accidents of mans life from the lines of the hand, withal its dimentions and significations. As also that most useful piece of astrology (long since promised) concerning elections for every particular occasion, now plainly manifested from rational principles of art, not published till now (London: G. Sawbridge, 1663), 2 parts.
 C. Rider, Rider’s British Merlin (London, c. 1690). Saunder’s pseudonym, [S]chardanus Rider, is an anagram. None of Newton’s personal copies of Saunder’s works have been preserved.
 H. More, Tetractys Anti-Astrologica; or, the four chapters in the explanation of the Grand Mystery of Godliness, which contain a brief but solid confutation of Judiciary Astrology (London, 1681). This is an excerpt from a work published in 1660. Again, Newton’s personal copy, which was presented to him by the author and which is now kept in the Beinecke Library of Rare Books at the Yale University (New Haven), shows no signs of regular use.
 Unfortunately, Newton did not name the author of this work. The fact that Saunder’s treatise on palmistry and astrology was issued in that same year strongly suggests that Newton’s personal copy was indeed purchased on that occasion.
 Conduitt’s biography was never published but his notes have been preserved and are cited in D.T. Whiteside, M.A. Hoskin & A. Prag (eds.), The Mathematical Papers of Isaac Newton (Cambridge: Cambridge University Press, 1967), vol. 1, pp. 15-19.
 De Moivre’s unpublished memorandum is cited in Whiteside et al. [n. 13], op. cit., vol. 1, pp. 5-6.
 L.T. More, Isaac Newton: A Biography (New York: Charles Scribner’s Sons, 1934 [reprint Dover Publications Inc., New York, 1962]), pp. 32-33.
 D. Brewster, The Life of Sir Isaac Newton (London: John Murray, 1831), pp. 13-14; D. Brewster, Memoirs of the Life, Writings, and Discoveries of Sir Isaac Newton (Edinburgh/London: Thomas Constable & Co./Hamilton, Adams & Co., 1855 [reprint Johnson Reprint Corporation, New York/London, 1965]), vol. 1, pp. 21-24.
 R.S. Westfall, Never at Rest: A Biography of Isaac Newton (Cambridge: Cambridge University Press, 1980), pp. 88 & 98.
 Cf. B.J.T. Dobbs, The Foundations of Newton’s Alchemy, or “The Hunting of the Greene Lyon” (Cambridge: Cambridge University Press, 1975); B.J.T. Dobbs, The Janus Face of Genius: The Role of Alchemy in Newton’s Thought (Cambridge: Cambridge University Press, 1991).
 Cf. F.E. Manuel, The Religion of Isaac Newton (Oxford: Clarendon Press, 1974).
 I.B. Cohen, “Isaac Newton – An Advocate of Astrology?”, Isis, 33 (1941), 60-61.
 Brewster [n. 16], Life ..., p. 339; Memoirs ..., vol. 2, pp. 164-165 & 408.
 Brewster [n. 16], Life ..., p. 339, attributes the anecdote to the astronomer Nevil Maskelyne (1732-1811), from 1765 director of the Greenwich Observatory, who passed it on to the Oxford professor in astronomy, Stephen Peter Rigaud (1774-1839).
 Brewster [n. 16], Memoirs ..., vol. 2, p. 165; Westfall [n. 17], op. cit., p. 590 (n. 136).
In a recent study James Frazier has correctly pointed out that my quote from Cowling (1977) was inaccurately phrased in my original paper. Citing Whiteside, I should have written “he never found any reference to horoscopes among [...]”. There are of course several references to astrology in Newton’s writings regarding alchemy and biblical chronology but none of these support the claim that Newton had an interest in traditional or judicial astrology.
James Frazier’s detailed study Contested Iconography: Was Isaac Newton an Astrologer, a Rational Mechanistic Scientist, or Neither? can be downloaded from the following web link.
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