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the case of 2a moved by If is imaginary, so must be his additional resistance. And here again, I am at a loss to discover any effect of the vis inertia.

In No. 6, he tells us, "that all this is likewise certain when taken the contrary way, viz. from motion to rest; for the body a, moving with a certain velocity, as c, requires a certain degree of force or resistance to stop that motion," &c. &c.; that is, in other words, equal force is necessary to destroy force. It may be so. But how does that discover a vis inertia? Would not the effect be the same, if there were no such thing? A force If strikes a body la, and moves it with the celerity le, that is, with the force 1f; it requires, even according to our author, only an opposing If to stop it. But ought it not (if there were a vis inertia) to have not only the force If, but an additional force equal to the force of vis inertia, that obstinate power by which a body endeavours with all its might to continue in its present state, whether of motion or rest? I say, ought there not to be an opposing force equal to the sum of these? The truth, however, is, that there is no body, how large soever, moving with any velocity, how great soever, but may be stopped by any opposing force, how small soever, continually applied. At least, all our modern philosophers agree to tell us so.

Let me turn the thing in what light I please, I cannot discover the vis inertia, nor any effect of it. It is allowed by all, that a body la, moving with a velocity lc, and a force If, striking another body la at rest, they will afterwards move on together, each with c and f; which, as I said before, is equal in the whole to lc and lf. If vis inertiæ, as in this case, neither abates the force nor the velocity of bodies, what does it, or how does it discover itself?

I imagine I may venture to conclude my observations

ou this piece, almost in the words of the author; that, if the doctrines of the immateriality of the soul and the existence of God, and of divine providence, are demonstrable from no plainer principles, the deist (that is, theist) has a desperate cause in hand. I oppose my theist to his atheist, because I think they are diametrically opposite; and not near of kin, as Mr. Whitefield seems to suppose, where (in his Journal) he tells us, "M. B. was a deist, I had almost said an atheist;" that is, chalk, I had almost said charcoal.

The din of the Market* increases upon me; and that, with frequent interruptions, has, I find, made me say some things twice over; and, I suppose, forget some others I intended to say. It has, however, one good effect, as it obliges me to come to the relief of your patience with

Your humble servant,

B. FRANKLIn.

TO CADWALLADER COLDEN.

Baxter's Book on the Vis Inertia of Matter.- Manufacture of Electrical Apparatus. -Colden's Philosophical Treatise.

SIR,

Philadelphia, 6 August, 1747.

The observations I sent you on Baxter's book were wrote on a sheet or two of paper in folio.† He builds his whole argument on the vis inertia of matter.

* Philadelphia Market, near which Dr. Franklin lived.

+ Probably the same in substance as the preceding letter to Mr. Hopkinson. Enitor.

I

boldly denied the being of such a property, and endeavoured to demonstrate the contrary. If I succeeded, all his edifice falls of course, unless some other way supported. I desired your sentiments of my argument. You left the book for me at New York, with a few lines containing a short censure upon the author, and that your time had been much taken up in town with business, but you were now about to retire into the country, where you should have leisure to peruse my papers; since which I have heard nothing from you relating to them. I hope you will easily find them, because I have lost my rough draft; but do not give yourself much trouble about them; for if they are lost, it is really no great matter.

I am glad to hear, that some gentlemen with you are inclined to go on with electrical experiments. I am satisfied we have workmen here, who can make the apparatus as well to the full as that from London; and they will do it reasonably. By the next post, I will send you their computation of the expense. If you shall conclude to have it done here, I will oversee the work, and take care that every part be done to perfection, as far as the nature of the thing admits.

Instead of the remainder of my rough minutes on electricity, (which are indeed too rough for your view,) I send you enclosed copies of two letters I lately wrote to Mr. Collinson on that subject. When you have perused them, please to leave them with Mr. Nichols, whom I shall desire to forward them per next post to a friend in Connecticut.

I am glad your Philosophical Treatise meets with so good reception in England. Mr. Collinson writes the same things to Mr. Logan; and Mr. Rose, of Virginia, writes me, that he had received accounts from his correspondents to the same purpose. I perceive by the

papers, that they have also lately reprinted, in London, your "History of the Five Nations" in octavo. If it come to your hands, I should be glad to have a sight of it.

Mr. Logan,* on a second reading of your piece on Fluxions lately, is satisfied, that some of the faults he formerly objected to it were his own, and owing to his too little attention at that time. He desires me to tell you so, and that he asks your pardon. Upon what Mr. Collinson wrote, he again undertook to read and consider your Philosophical Treatise.† I have not seen

* James Logan, who came to America with William Penn, and who was distinguished for his attainments in classical literature, and in almost every branch of science, as well as for his public services for nearly half a century in Pennsylvania. — EDITOR.

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The title of this treatise, as originally printed, was as follows; Explication of the first Causes of Action in Matter; and of the Cause of Gravitation. London, 1746." A second edition enlarged was published five years afterwards with a different title, namely; "The Principles of Action in Matter, the Gravitation of Bodies and the Motion of the Planets explained from those Principles. By Cadwallader Colden, Esquire. London. Printed for Dodsley. 1751." The book was dedicated to the Earl of Macclesfield, then President of the Royal Society. Appended is a chapter entitled, "An Introduction to the Doctrine of Fluxions, or the Arithmetic of Infinities; in order to assist the Imagination in forming Conceptions of the Principles on which that Doctrine is founded." The volume contains eight chapters, besides the one on Fluxions, is printed in quarto, and extends to two hundred and fifteen pages.

Mr. Colden seems not to have been satisfied with the manner in which the first edition found its way to the public. In the Preface to the second edition he says;

"A few copies of the two first chapters of this treatise were published at New York, with design to know the sentiments of the learned on new principles in natural philosophy or physics, which were advanced in that essay. The London edition was without the author's knowledge, and had never been made, could he have prevented it. Since that time, he has been encouraged to go on. In this edition the two first chapters are revised, the matters contained in them follow more consequentially, come obscurities are removed, the sentiments, it is hoped, put in a clearer light, and some new theorems added. In the following chapters, which were not before published, these principles are applied to the explication

him since, but shall soon, and will send you his sentiments. I am, Sir,

With great respect,

Your most humble servant,

B. FRANKLIN.

of the motions of the planets, and of the phenomena thereon depending, and of some other general phenomena. the causes of which, the author thinks, have not been before discovered."

The following extract from the Preface will exhibit to the reader an outline of Mr. Colden's views, and of the principles he attempts to establish.

"It is laid down as a principle, that all the primary or simple ideas we have of things external to us arise from the impressions or actions of these things on our senses; and, therefore, that the properties and qualities of things are nothing else but their various actions, or modes of acting, either simply or complicated; that the knowledge we have of things is no more than the perception of these actions, of their different degrees and different modes, and of the ratios of these differences to each other.

"That all simple beings or things have one single action, or manner of acting, essential to them; without which we have no conception of a thing.

"That there are two, and perhaps only two, essential different modes of action in material beings. The one, a power by which the thing, in which this action subsists, does resist all change of its present state; the other, a power by which the thing, in which the action of moving subsists, is continually changing its present state, or situation, by motion, and gives motion to every other thing, which at any time moves.

"It is a self-evident proposition, that nothing acts where it is not; therefore, if any thing exert any action at a distance, this action must be communicated to that distance, by some medium from the place of the acting thing, to the place where the action is communicated. The mutual apparent attraction of bodies at a distance from each other shows the necessity of the existence of such a medium. This medium makes a third kind of matter, essentially different from the other two, by its equally receiving the action, or manner of acting, either of the resisting or of the moving power, and by its reacting those actions with the same degree of force or action it received them. From the nature of this medium (commonly called ether), or from the necessary consequences of receiving and reacting these contrary modes of action, the apparent mutual attraction of bodies at a distance from each other, and gravitation, are explained, and the several phenomena thence arising.

Every thing to which any action is essential, must exert that action equally in all directions; because nothing can be conceived in the thing

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