Letters about Isaac Newton

Image: John Witherspoon. Unidentified Artist after Charles Peale. Princeton University. https://artmuseum.princeton.edu/collections/objects/45198

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The Reverend John Witherspoon was a staunch Presbyterian minister who came from Scotland to assume the presidency of the College of New Jersey in 1768. He served as a delegate to the Continental Congress, supported the Revolution vigorously, and contributed much to his adopted country. Not the least of his contributions was his introduction of the finest thought of the Scottish Enlightenment into the curriculum of the college. He was an inspiring teacher who transmitted to his students an intense regard for the study of science. James Madison, Hugh Henry Brackenridge, and Philip Freneau were among the leaders of the period who felt his influence. One of the most striking instances of Witherspoon’s interest in science was his unhesitating expenditure of the meager funds of the college for the orrery or mechanical planetarium constructed by the ingenious Pennsylvania clockmaker, David Rittenhouse.

Witherspoon, however, was a theologian and general scholar rather than a scientist, and even in expounding moral philosophy and religion his success was greater in arousing controversy than in developing original ideas. 1 It has always been assumed that in the sciences he was a Newtonian, but it has been difficult to assess his competence in these fields. 2 One very clear appraisal is available in an interchange to which he contributed an anonymous letter over the signature “J.W.” in the Pennsylvania Magazine for 1776. 3

He offered his essay by way of approving a diffuse attack upon Newtonian theories by the Reverend Matthew Wilson of Lewes, Delaware, which had appeared in the two preceding numbers of the magazine. 4 Wilson’s “Proposal for Reducing Natural Philosophy to a System” was in the tradition of oblique resistance to the immortal mathematician which had continued from his own day. Sir Isaac Newton and his physical laws commanded great esteem in the eighteenth century but there was always a current of resistance which frequently recurred to Cartesian principles. Another foundation for opposition was demonstrated by those intuitive thinkers, among them many clergymen, who distrusted the blind faith placed in Newton’s laws. They felt that there must be error in all things human and that Newton’s works could be no exception. This frame of mind was very well illustrated in Witherspoon’s essay, printed below.

This dull and muddled piece has several points of similarity with that of the Reverend Thomas Prince of Boston, who in 1755 had provoked a now famous controversy with Professor John Winthrop by asserting that a recent earthquake might have been caused by man’s impiety in erecting lightning rods. Winthrop successfully countered the suggestion in a published lecture on the nature of earthquakes.

John Winthrop’s role was performed in 1776 by David Rittenhouse, who by then was an astronomer and mathematician of established reputation. Indeed, Rittenhouse’s prestige, based upon the orrery and upon his observations of the transit of Venus in 1769, was quite remarkable. Of this, he made no use in his reply, which was even more anonymous than Witherspoon’s, being signed only with an “R.” Had he used “D.R.” it may be doubted whether anyone would have been fooled; possibly, even the “R.” deceived but few.5

Rittenhouse’s reply must have been a great surprise, especially in the strength of feeling it revealed, for the Philadelphian was the most modest of men. In just two sharply etched paragraphs, he cut through the obfuscations of Witherspoon’s letter to reveal the untruth of the most concrete charge presented. He did not bother commenting on Matthew Wilson’s piece. His attack was keen and vehement and it ended the matter. Witherspoon never again published anything in this area of thought. 6

The two letters provide a striking contrast between the man of broad but unspecialized learning and the technically competent scientist who could not tolerate wandering philosophical speculation erected upon ignorance of scientific fundamentals.

—TAH Staff



I have read with some attention the piece in your two last magazines under the title of A Proposal for reducing Natural Philosophy to a System, with Remarks on the Cartesian and Newtonian Theories, (123 & 173). The remarks are, I think many of them just and striking, and certainly merit the consideration of the adepts in natural science. I am however at a loss to discover why he has intitled his piece A Proposal, &c. for I can discover no proposal in any part of it, except an attempt to unsettle our belief of the Newtonian theory, which has been, for near a century past, implicitly received by all Englishmen. If he has any thing to propose I shall be glad to hear it, and in the mean time shall communicate a few reflections which occurred to me in reading his discourse.

In the first place, it will be very difficult for either him or me to procure attention at all to what may be offered in opposition to the Newtonian theory. A system of that kind when once generally received, people are unwilling to part with, and they are apt to despise the person as a fool who attempts to bring it into question. What! shall an obscure anonymous writer in a public magazine, pretend to oppose the philosophy of the great Newton? We are well assured that when Newton himself began his enquiries into nature, his first discoveries met with great opposition, and were often treated with contempt. In particular it was long before they would pay any regard to him in France, where the system of Des Cartes had been firmly established. At last, however, it prevailed universally in England, and pretty generally through the rest of Europe. As Des Cartes overthrew the occult qualities and substantial forms of Aristotle, Newton destroyed or brought into disrepute the vortices and subtle matter of Des Cartes.

Shall we then hear any thing against Newtonian principles in America? I answer, Yes. And I will first plead for your correspondent, and then assist him by a few observations similar to his own. I will plead for him by an argument that does no dishonour to Sir Isaac Newton, further than showing that he was not wholly free from the weakness of humanity. He can never be enough extolled for his resolution to lay aside all opinions and principles, and take nature just as it was by an induction of experiments: So far as he adhered to his own plan, he did inexpressible service to philosophy, and made amazing advances in the knowledge of nature. In this circumstance he had manifestly the advantage of Des Cartes, who confessedly endeavoured to explain, not causes from effects, but effects from causes. Thus, he says, Perspicuum est optimam plzilosophandi, viam nos secuturos si ex ipsius Dei cognitione rwum, ab eo Creatorum [explicationem] deducere conemur ut ita scientiam prefectissimam quae est eflectuum per causas acquiramus, Cartes Prin. part 2. sect. 22.7

But notwithstanding this promising outset of Sir Isaac, it remains to be examined whether he did not in some degree forget his own plan, and sometimes assume principles to account for his facts, which were neither quite certain in themselves, nor, though true, sufficient to account properly for the phenomena to which he applied them. This is what I wish to see enquired into with impartiality in the manner of M. W.’s essay, and as an example of it, shall propose to the Newtonians, at present,

A few Thoughts on Space, Dimension, and the Divisibility of Matter in Infinitum.

I class these three together, because the two latter will serve to illustrate what is to be considered of the former. It is not without reason that, in the present philosophy, space is always considered in the first place; because without admitting space void of matter, the whole system falls to the ground of course.

The necessary subserviency that such space is of to this philosophy, is a proof that it is founded upon principles as occult as those of the peripatetics, which are at present treated with so much derision. But though some of the occult qualities of these ancient philosophers can now be explained, it is not handsome in the present philosophers to despise their ignorance, seeing they only acted the same part then, these do now, of resolving such things into principles and laws as they could not account for.

But the present philosophers have really done worse, for they have actually assumed a principle, or rather a new-invented kind of being, called Empty Space, in order to render their occult principles consequently necessary: for where nothing is between bodies, nothing to be sure can agitate or move them, but some insensible properties inseperable from their sensible ones. Now, though Aristotle and his numerous followers, supplyed their ignorance with terms of art, which stood for principles; yet they never assumed any previous maxim, which while received, prevented any possibility of discovering whether their occult qualities were any thing else but what they called them.

This same infinite space is the most wonderful thing within the whole range of being; to enumerate its contrary definitions is impossible. It is neither God nor his creature; and yet it is inseparable from the being either of God or of any thing he can create. All matter is space whatever more it is; for space is an essential property of matter, it is in space, and space is in it: Wherever matter is, there is space; and there space would be, though matter were not there. The same holds just as true with relation to it and spirit, or it and God: It is infinite both in its extension and duration; it is immoveable and indivisible. If a complete definition of it were put into a lady’s pocket-book, I am persuaded there is not a woman that wears one, but would positively guess it to be an enigma for Nothing; and she would be astonished to be told, that, in the judgment of the learned, it is the quintessence of a most learned, most metaphysical, and most subtle argument maintained upon the subject of space, by one of the most celebrated divines and philosophers that the last or any age has produced.

The only positive idea applied to space is extension; but we can apply no idea to any subject, which the subject itself does not impress. Matter forces upon our senses the idea or image of its dimension or extension. It is philosophical felony to steal an image which nature gives us, and invest a subject with it that never excited any idea in us, and consequently has no existence to us: We create nothing into a being, by applying ideas to it which we derive from something. Space is only one of the ideas excited by matter, and by the power of the mind abstracted from its subject, just as we can image a colour to ourselves, without connecting in our apprehension a subject with it wherein it exists: A little more of the same metaphysics which can prove that nothing is extended, will prove that space is purple. But why should I say purple? Space is of all colours, if light is reflected by vacuum and not by matter. It is a very ingenious contrivance in philosophers to render Nothing a subject of enquiry and conception, by dressing it in a suit of cloaths borrowed from Something.

Now space, or extension, being certainly a necessary or essentially constituent property of matter, the philosophers affirm to us that matter is divisible in infinitum, at the same time they have determined punctually, that space is absolutely indivisible: This savours rankly of contradiction. The more modest friends of this philosophy are willing to interpret the doctrine of the infinite divisibility of matter, not as an assertion of the actual possibility of dividing any parcel of matter without end, but as a mathematical possibility of conceiving its extension eternally divisible into lesser and lesser extensions. So far the concession is just; for what God created a unit, the nisus of the whole creation upon it could not bruise or separate into two; indivisibility is one of its essential inherent properties. But then do they not still propose a palpable contradiction, by maintaining its dimension, or the space its surface measures is divisible infinitely, while they assert at the same time that space itself is indivisible?

I lately saw a very pretty, tho’ common and simple experiment exhibited, relative to and intended to illustrate the common doctrine of space; which this is therefore a proper place to make a natural reflection upon. The experiment shewed, that by an image formed in the air, at a certain distance between the concave speculum, and any person looking into it, extension and form became an object of sense, where their exists neither solidity nor sensible resistance. But that does not prove that an image can be formed in empty space, or where there is no matter; unless we can prove first, there can be no matter where we are not sensible of resistance. But on the contrary, I infer from that phenomenon, that these spaces, which in a loose and incorrect sense we call empty, are as full of matter as these in which the most solid bodies are: For as our senses can only be effected by matter, they are certain infallible standards for determining where matter is; so that we may be as assured of a fulness of matter where we see any thing, though we cannot feel it, as we could be certain there was matter where we felt it, though we could not see it, or though it were the nature of that matter to be invisible; as I presume would be the case of all solid atoms, though each were as big as a milstone, for it is owing to the interstices in bodies that they become visible.--All reflected images conspire, I apprehend, to prove, that as it is their property by means of light to affect our sense of seeing, so wherever an object can be formed to affect that sense, there must be as great a fulness of matter as in the original object, from whence the image was trajected to these spaces where it is again renewed.

Though the infinite divisibility of any given extension may be easily perceived to be a metaphysical or mathematical sophism, as I must take the liberty to call the whole doctrine of infinites, especially as pretended to be canvassed by mighty finite capacities, and though it is not easy to adduce a precise refutation of such inconceivable refinements, yet the Newtonian philosophy, by the relation it establishes between power and distance, in the doctrine of gravitation, has furnished us with a direct disproof of this. For if the power of gravitation between bodies be as the squares of their distances; and if at any given distance (no matter whether we call it a yard or a thousand miles) the power of their tendency towards each other is equal to any given number; then at half that distance, the power will be four times as much, and so on. Hence it must follow, that if that distance is divisible into infinite parts, that power of attraction between them will increase infinitely beyond all calculation: But this is grossly false in fact; for we know when bodies come into actual contact, by means of this supposed power, their resistance to separation again, or tendency to unite, is very limited, and easily overcome by an excessively finite power. Therefore as at contact, which is at the end of distance, the power of attraction is finite, of consequence the spaces they traverse before they meet cannot be infinitely divisible. And no demonstration, no not a mathematical one, can be true, which implies a flat contradiction.

I am, Sir, yours, &c.

J. W.


I Am one of those who are ready to subscribe to the general maxim, That perfection is not to be found in any thing human; and therefore do not suppose the Newtonian philosophy to be so perfect as not to admit of amendment. But I must confess that almost all the attempts to controvert that philosophy which I have met with, amount to nothing more than so many proofs that those who made them did not understand it. 09 this kind are the objections started by your correspondent J. W. I shall neither spend my own time, nor trouble you with pointing out at present more than one of the several mistakes he has fallen into. He endeavours to prove, either that extension is not infinitely divisible, or that a fundamental principle of the Newtonian philosophy is not true. "For, says he, if the power of gravitation between bodies be [inversely, he ought to have said] as the squares of their distances. . . ." [Here Rittenhouse went on to quote Witherspoon’s suggestion that Newton’s laws demanded an infinite force of attraction between bodies in contact.]

This gentleman would have found no contradiction at all in the case, if he had remembered, as he ought to have done. First, That the Newtonian Philosophy informs us, that the force of attraction between regular bodies, is inversely as the squares of the distances of their centers; and not in any case inversely as the distances of their nearest surfaces, which his argument supposes. Secondly, That as soon as the center of one body enters the surface of another homogenious body, this rule ceases, and another, more simple, takes place, viz. the force of attraction decreases, directly as the distance of the centers decreases. I say, if he had considered this, he would have seen that he could not, by any infinite divisibility of extension, produce an infinitely great force of attraction; though he might a force less than any assignable. I wish the gentleman would be more cautious for the future; as well on his own account, as for the sake of your readers, some of whom may be misled by the weakest reasoning, on a subject which they do not understand. And I will venture to assure him, that the whole doctrine of infinites, which he is pleased to call a sophism, will not produce one contradiction in a mathematical head. Those of another cast need not meddle with it; since there are a sufficient variety of literary subjects to engage every man according to the bent of his genius.

I am, Sir, yours, &c.


  1. 1. Douglass Adair, "James Madison," in The Lives of Eighteen from Princeton ed. Willard Thorp (Princeton, 1946), pp. 140-141.
  2. 2. Francis L. Broderick, "Pulpit, Physics, and Politics: The Curriculum of the College of New Jersey, 1746-1794," William and Mary Quarterly, jd Ser., VI (Jan. 1949) 9 64-67.
  3. 3. 3Pennsylvania Magazine, I (May 1776), 225-229. "J. W." was positively identified in 1813 by Benjamin Smith Barton in William Barton, Memoirs of the Life of David Rittenhouse (Philadelphia, 1813), p. 604, and the identification was accepted by Witherspoon’s biographer, V. L. Collins, President Witherspoon (Princeton, 1925), II, 251. The letter, however, has apparently never been reprinted or used as an indication of Witherspoon’s capacities and attitudes in science. Return to text
  4. 4. Pennsylvania Magazine, I (Mar. and Apr. 1776), 123-128, 173-176. "M. W." was tentatively but reasonably identified as Matthew Wilson by William Barton, Memoirs of Rittenhouse, pp. 257-258.
  5. 5. Pennsylvania Magazine, I (Mar. and Apr. 1776), 123-128, 173-176. "M. W." was tentatively but reasonably identified as Matthew Wilson by William Barton, Memoirs of Rittenhouse, pp. 257-258.
  6. 6. Pennsylvania Magazine, I (June 1776), 282-283. Rittenhouse was identified as the author by both Benjamin Smith Barton and William Barton, Memoirs of Rittenhouse, pp. 260, 604.
  7. 7. At least no such work is to be found among his pamphlets or in his collected works (The Works of the Reverend John Witherspoon, 4 vols. [Philadelphia, 1800-02].
  8. 8. Several errors and omissions were made in the printing of this passage, the worst of which have been corrected. Even the reference was wrong. The passage appeared in Renati DesCartes, Principire Philosophire (Amstelodami, 1656), part I, section 24, p. 3. In translation, it reads: "We will clearly follow the best way of philosophizing if we try to deduce an explanation of the things created by him from our knowledge of God himself, so that we may acquire the most perfect science, that is the knowledge of effects through their causes."
  9. 9. Robert Aitken was the publisher of the magazine.
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