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Hall will do his best to dispose of them, and I will assist him what I can. They may send a Parcel also to Mr. Parker, Printer of New York, a very honest punctual Man.

I am glad all the Bills I sent you have been paid or accepted. You may expect more in a short time; and after the next Parcel of Books are paid for, you will chiefly have to deal with Mr. Hall, into whose Hands I have agreed to put the Shop, etc.

With all our best Respects to you and yours, heartily wishing you Health and Happiness, I conclude your obliged humble Servt,

per Mesnard.

B. FRANKLIN.

63. TO JOHN FRANKLIN'

(A. P. S.)

Augt 6. 1747.

DEAR BROTHER I am glad to hear that Mr Whitefield is safe arriv'd, and recovered his Health: he is a good Man and I love him:

Mr Douse has wrote to me per this Post, at Mrs Steele's Request desiring an Explanation from me with regard to my Dissatisfaction with that Lady. I have wrote him in answer that I think a Misunderstanding between Persons at such a Distance, and never like to be further acquainted, can be of no kind of Consequence, & therefore had better be dropt and forgot than committed to Paper; but that however, if Mrs Steele after Recollection still desires it, I will be very particular with her in a Letter for that purpose to herself. If such a Letter should be written, I will send you a Copy of it, for your & Sister's Satisfaction; but think 'twill be best that you do [not] show it, or any of the Letters in

1 Rough Draft in A. P. S.

which I have mention'd her nor speak of them, but keep quite unconcern'd for perhaps there may be a little Squabble.

With Love to Sister, &c. &c. I am, Sir

Your affectionate Brother

B. FRANKLIN.

64. TO CADWALLADER COLDEN1 (L. C.)

Philadelphia, 1747.

ACCORDING to my promise, I send you in writing my observations on your book; you will be the better able to consider them; which I desire you to do at your leisure, and to set me right where I am wrong.

I stumble at the threshold of the building, and therefore have not read further. The author's vis inertia essential to matter, upon which the whole work is founded, I have not been able to comprehend. And I do not think he demonstrates at all clearly (at least to me he does not), that there is really such a property in matter.

He says, No. 2, "Let a given body or mass of matter be called a, and let any given celerity be called c. That celerity doubled, tripled, &c., or halved, thirded, &c., will be 2c, 3c, &c., or c, c, &c., respectively. Also the body doubled, tripled, or halved, thirded, will be 2a, 3a, or fa, ja, respec

1 This letter has hitherto been supposed to have been addressed to Thomas Hopkinson. There are two transcripts of it in the Library of Congress. I have printed from Benjamin Vaughan's copy. The book referred to was "An Inquiry into the Nature of the Human Soul, wherein its Immortality is evinced," etc., by Andrew Baxter. The thesis which the author attempts to maintain rests upon the belief that nature is essentially inert and that all changes in it argue the action of an immaterial principle and consequently of the superintendence of a divine power. ED.

tively." Thus far is clear. But he adds, "Now to move the body a, with the celerity c, requires a certain force to be impressed upon it; and to move it with a celerity as 2c, requires twice that force to be impressed upon it, &c." Here I suspect some mistake creeps in, by the author's not distinguishing between a great force applied at once, and a small one continually applied, to a mass of matter, in order to move it. I think it is generally allowed by the philosophers, and, for aught we know, is certainly true, that there is no mass of matter, how great soever, but may be moved by any force how small soever, (taking friction out of the question,) and this small force, continued, will in time bring the mass to move with any velocity whatsoever. Our author himself seems to allow this towards the end of the same No. 2, when he is subdividing his celerities and forces; for as in continuing the division to eternity by his method of c, c, &c, fc, &c. you can never come to a fraction of velocity that is equal to oc, or no celerity at all; so, dividing the force in the same manner, you can never come to a fraction of force that will not produce an equal fraction of celerity.

Where then is the mighty vis inertia, and what is its strength, when the greatest assignable mass of matter will give way to, or be moved by, the least assignable force? Suppose two globes equal to the sun and to one another, exactly equipoised in Jove's balance; suppose no friction in the centre of motion, in the beam or elsewhere; if a musketo then were to light on one of them, would he not give motion to them both, causing one to descend and the other to rise? If it is objected, that the force of gravity helps one globe to descend, I answer, the same force opposes the other's rising. Here is an equality that leaves the whole

motion to be produced by the musketo, without whom those

What then does vis other effect could we

globes would not be moved at all. inertia do in this case? and what expect if there were no such thing? Surely, if it were any thing more than a phantom, there might be enough of it in such vast bodies to annihilate, by its opposition to motion, so trifling a force !

Our author would have reasoned more clearly, I think, if, as he has used the letter a for a certain quantity of matter, and c for a certain quantity of celerity, he had employed one letter more, and put ƒ, perhaps, for a certain quantity of force. This let us suppose to be done; and then, as it is a maxim that the force of bodies in motion is equal to the quantity of matter multiplied by the celerity, (or f= c x a); and as the force received by and subsisting in matter, when it is put in motion, can never exceed the force given; so, if f moves a with c, there must needs be required 2f to move a with 2c; for a moving with 2c would have a force equal to 2f, which it could not receive from if; and this, not because there is such a thing as vis inertia, for the case would be the same if that had no existence; but because nothing can give more than it has. And now again, if a thing can give what it has, if if can to 1a give Ic, which is the same thing as giving it If, (that is, if force applied to matter at rest, can put it in motion, and give it equal force,) where then is vis inertiæ ? If it existed at all in matter, should we not find the quantity of its resistance subtracted from the force given?

In No. 4, our author goes on and says, "The body a requires a certain force to be impressed on it to be moved with a celerity as c, or such a force is necessary; and therefore it makes a certain resistance, &c.; a body as 2a requires

twice that force to be moved with the same celerity, or it makes twice that resistance; and so on." This I think is not true; but that the body 24, moved by the force if, (though the eye may judge otherwise of it) does really move with the same celerity as it did when impelled by the same force; for 20 is compounded of 1a + 1a; and if each of the 1a's, or each part of the compound, were made to move with Ic (as they might be by 2f), then the whole would move with 2c, and not with Ic, as our author supposes. But if applied to 20 makes each a move with c; and so the whole moves with ic; exactly the same as 1a was made to do by if before. What is equal celerity but a measuring the same space by moving bodies in the same time? Now if 1a, impelled by If, measures one hundred yards in a minute; and in 2a, impelled by if, each a measures fifty yards in a minute, which added make one hundred; are not the celerities, as the forces, equal? And, since force and celerity in the same quantity of matter are always in proportion to each other, why should we, when the quantity of matter is doubled, allow the force to continue unimpaired, and yet suppose one half of the celerity to be lost? I wonder the more at our author's mistake in this point, since in the same number I find him observing; "We may easily conceive that a body, as 34, 4a, &c., would make three or four bodies equal to once a, each of which would require once the first force to be moved with the celerity c." If then, in 3a, each a requires once the first force f, to be moved with the celerity c, would not each move with the force f, and celerity c? and consequently the whole be 3a moving with 3f and 3c? After so distinct an observation, how could he miss of the consequence, and imagine that Ic and 3c were the same? Thus, as our

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