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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.f I have not seen him since, but shall soon, and will send you his sentiments. I am, Sir,

* 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.

f 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, some 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

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.

"[t 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.

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

A Conjecture as to the Cause of the Heat of the Blood in Health, and of the Cold and Hot Fits of some Fevers.*

The parts of fluids are so smooth, and roll among one another with so little friction, that they will not by any (mechanical) agitation grow warmer. A phial half full of water shook with violence and long continued, the water neither heats itself nor warms the phial. Therefore the blood does not acquire its heat either from the motion and friction of its own parts, or its friction against the sides of its vessels.

But the parts of solids, by reason of their closer adhesion, cannot move among themselves without friction, and that produces heat. Thus, bend a plummet to and fro, and, in the place of bending, it shall soon grow hot. Friction on any part of our flesh heats it. Clapping of the hands warms them. Exercise warms the whole body.

The heart is a thick muscle, continually contracting and dilating near eighty times in a minute. By this motion there must be a constant interfrication of its constituent solid parts. That friction must produce a heat, and that heat must consequently be continually communicated to the perfluent blood.

itself to hinder it, in one direction more than another. Then the direction of motion in the moving power, towards any one point more than towards any other point, must be by something external, by the resistance in that particular direction being less than in any other.

"Several arguments are produced, in this essay, to demonstrate, that light is the substance or thing to which the power of moving is essential; and to those therein mentioned, among which the principal is the demonstrating in what manner the motions of the planets and comets arise from thence, this other argument may be added, that we can have no conception of light without motion, of which any one may convince himself by a proper attention. For example, if light be supposed to be composed of small globular bodies at rest, this supposition gives no idea of light or colors; it conveys no idea of any thing in common with the ideas raised in our mind by the action of light." — Editor.

• This piece I have found in Franklin's handwriting among the papers of Cadwallader Colden. Its date is uncertain, but it was probably written before the year 1750. — Editor.

VOL. VI. 13 I

To this may be added, that every propulsion of the blood by the contraction of the heart, distends the arteries, which contract again in the intermission; and this distension and contraction of the arteries may occasion heat in them, which they must likewise communicate to the blood that flows through them.

That these causes of the heat of the blood are sufficient to produce the effect, may appear probable, if we consider that a fluid once warm requires no more heat to be applied to it in any part of time to keep it warm, than what it shall lose in an equal part of time. A smaller force will keep a pendulum going, than what first set it in motion.

The blood, thus warmed in the heart, carries warmth with it to the very extremities of the body, and communicates it to them; but, as by this means its heat is gradually diminished, it is returned again to the heart by the veins for a fresh calefaction.

The blood communicates its heat, not only to the solids of our body, but to our clothes, and to a portion of the circumambient air. Every breath, though drawn in cold, is expired warm; and every particle of the materia perspirabilis carries off with it a portion of heat.

While the blood retains a due fluidity, it passes freely through the minutest vessels, and communicates a proper warmth to the extremities of the body. But when by any means it becomes so viscid, as not to be capable of passing those minute vessels, the extremities, as the blood can bring no more heat to them, grow cold.

The same viscidity in the blood and juices checks

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