was not drawn by the heart, the compression of an artery would not empty a vein, and I conjecture that the pricking pain is occasioned by the sides of the small vessels being pressed together.

I am not without apprehension, that this hypothesis is either not new, or, if it is new, not good for any thing. It may, however, in this letter, with the enclosed paper on a kindred subject, serve to show the great confidence I place in your candor, since to you I so freely hazard myself (ultra crepidam) in meddling with matters directly pertaining to your profession, and entirely out of the way of my own. If you give yourself the trouble of reading them, it is all I can modestly expect. Your silence about them afterwards will be sufficient to convince me, that I am in the wrong, and that I ought to study the sciences I dabble in, before I presume to set pen to paper. I will endeavour, how

. ever, to make you some amends by procuring you from better judges some better remarks on the rest of your piece, and shall observe your caution not to let them know from whom I had it.

The piece on Fluxions I purpose shortly to read again, and that on the several species of matter, when you shall have what little I shall be able to say about them.

The members of our Society here are very idle gentlemen. They will take no pains. I must, I believe, alter the scheme and proceed with the papers I have, and may receive, in the manner you advise in one of your former letters. The mention of your former letters puts me in mind how much I am in arrear with you. Like some honest insolvent debtors, I must resolve to pay ready money for what I have hereafter, and discharge the old debt by little and little as I am able.

The impertinence of these mosquitos to me (now I am in the humor of writing) prevents a great deal of mine to you, so that, for once, they are of some use in the world. I am, Sir, Your most humble servant,

B. FRANKLIN.

TO CADWALLADER COLDEN.

On the Circulation of the Blood. — Proposal for pub

lishing a Philosophical Miscellany.

Philadelphia, 28 November, 1745. SIR, I shall be very willing and ready, when you think proper to publish your piece on gravitation, to print it at my own expense and risk. If I can be the means of communicating any thing valuable to the world, I do not always think of gaining, nor even of saving, by my business; but a piece of that kind, as it must excite the curiosity of all the learned, can hardly fail of bearing its own expense.

I must not pretend to dispute with you on any part of the animal economy. You are quite too strong for me. I shall just mention two or three little things, that I am not quite clear in.

If there is no contrivance in the frame of the auricles or ventricles of the heart, by which they dilate themselves, I cannot conceive how they are dilated. It is said, by the force of the venal blood rushing into them. But, if that blood has no force which was not first given to it by the contraction of the heart, how can it (diminished as it must be by the resisting friction of the vessels it has passed through) be strong enough to overcome that contraction ? Your doctrine of fermentation in the capillaries helps me a little; for, if the returning blood be rarefied by the fermentation, its motion must be increased; but, as it seems to me that it must by its expansion resist the arterial blood behind it, as much as it accelerates the venal blood before it, I am still somewhat unsatisfied. I have heard or read somewhere, too, that the hearts of some animals continue to contract and dilate, or to beat, as it is commonly expressed, after they are separated from the other vessels, and taken out of the body. If this be true, their dilation is not caused by the force of the returning blood.

I should be glad to satisfy myself, too, whether the blood is always quicker in motion, when the pulse beats quicker. Perhaps more blood is driven forward by one strong, deep stroke, than by two that are weak and light; as a man may breathe more air by one long common respiration, when in health, than by two quick, short ones in a fever. I applied the siphon I mentioned

a to you in a former letter to the pipe of a water-engine.

2

E is the engine; a, its pipe; b b b, the siphon; c and d, the two glass pipes communicating with the siphon. Upon working the engine, the water flowed through the siphon, and the glass tube c; but none was discharged through d. When I stopped with my finger the end of the siphon, the water issued at both glass tubes, with equal force, and on only half stopping the end of the siphon, it did the same. I imagine the sudden bending of the siphon gives such a resistance to the stream, as to occasion its issuing out of the glass tube c.

But I intend to try a farther experiment, of which I shall give you an account.

I am now determined to publish an American Philosophical Miscellany, monthly or quarterly. I shall begin with next January, and proceed as I find encouragement and assistance. As I purpose to take the compiling wholly upon myself, the reputation of no gentleman or society will be affected by what I insert of another's; and that perhaps will make them more free to communicate. Their names shall be published or concealed, as they think proper, and care taken to do exact justice to matters of invention, &c. I shall be glad of your advice in any particulars that occurred to you in thinking of this scheme; for, as you first proposed it to me, I doubt not but you have well considered it.*

I have not the original of Dr. Mitchell's tract on the Yellow Fever.f Mine is a copy I had taken, with his leave, when here. Mr. Evans will make a copy of it

for you.

I hope it will be confirmed by future experiment, that the yaws are to be cured by tar-water. The case you relate to Dr. Mitchell gives great hopes of it, and should

* It does not appear that this scheme was ever carried into execution. - Editor.

† Dr. John Mitchell was a learned physician and botanist, and Fellow of the Royal Society. He was a native of England, but came over and established himself in Virginia. Dr. Miller says, that “ he wrote ably on the yellow fever, as it appeared in Virginia in 1742; and that his instructive manuscripts on this subject fell into the hands of Dr. Franklin, by whom they were communicated to Dr. Rush.” — Miller's Retrospech, Vol. I. p. 318. - Editor.

be published, to induce people to make. trials. For, though it should not always succeed, I suppose there is no danger of its doing any harm.

As to your pieces on Fluxions and the different species of matter, it is not owing to reservedness that I have not yet ‘sent you my thoughts; but because I cannot please myself with them, having had no leisure yet to digest them. If I was clear, that you are anywhere mistaken, I would tell you so, and give my reasons with all freedom, as believing nothing I could do would be more obliging to you. I am persuaded you think, as I do, that he who removes a prejudice, or an

I error,

from your minds, contributes to their beauty, as he would do to that of our faces, who should clear them of a wart or a wen.

I have a friend gone to New York with a view of settling there, if he can meet with encouragement. It is Dr. John Bard, whom I esteem an ingenious physician and surgeon, and a discreet, worthy, and honest

If, upon conversation with him, you find this character just, I doubt not but you will afford him your advice and countenance, which will be of great service to him in a place where he is entirely a stranger, and very much oblige, Sir, Your most humble servant,

B. FRANKLIN.

man.

P. S. I shall forward your letter to Dr. Mitchell. Thank you for leaving it open for my perusal

.

* This introduction was the origin of a long and intimate friendship between Dr. Bard and Mr. Colden. For his professional skill, his active public spirit, and his private worth, no man of his time was more highly valued than Dr. John Bard. His talents and his virtues were inherited by his son, Dr. Samuel Bard, of whom a very interesting memoir has been published by Professor M• Vickar. In that work, speaking of Dr. John Bard, the father, Professor Mo Vickar says; “He was a man who VOL. VI. 10

G