I thank you for the merino wool. It is a curiosity. Mr. Roberts promises me some observations on husbandry for you. It is one Mr. Masters, that makes manure of leaves, and not Mr. Roberts. I hope to get the particulars from him soon.

I have a letter from Mr. Collinson, of July 19th, in which he says; "Pray, has Mr. Eliot published any addition to his work? I have Nos. 1 and 2. If I can get ready, I will send some improvements made in the sandy parts of the county of Norfolk. By the way, it is a great secret, but it is Mr. Jackson's own drawing up, being experiments made on some of his father's estates in that county; but his name must not be mentioned. I thank you for the fowl meadow grass. I sowed it June 7th, as soon as I received it, but none is yet come up. I don't know how it is, but I never could raise any of your native grasses; and I have had a variety from J. Bartram of curious species."

In another, of September 26th, he says, "I am much obliged to thee for Mr. Eliot's Third Essay. I have sent Maxwell's 'Select Transactions in Husbandry.' If Mr. Eliot has not seen them, they may be very useful to him. I have prevailed on our worthy, learned, and ingenious friend Mr. Jackson to give some dissertations on the husbandry of Norfolk, believing it may be very serviceable to the colonies. He has great opportunities of doing this, being a gentleman of leisure and fortune, being the only son, whose father has great riches and possessions, and resides every year, all the long vacation, at his father's seat in Norfolk. After J. Bartram has perused it, I shall submit how it may be further disposed of, only our friend Eliot should see it soon; for Jackson admires his little Tracts of Husbandry, as well as myself, and it may be of greater service to him and his colony, than to yours." "The fowl meadow

VOL. VI.

15

J*

grass has at last made its

appearance. Another year Thus far friend Collinson.

we shall judge better of it." You may expect the papers in a post or two. If you make any use of them, you will take care not to mention any thing of the author.

The bearer is my son, who desired an opportunity of paying his respects to you in his return from Boston. He went by sea.

They have printed all my electrical papers in England, and sent me a few copies, of which I design to send you one per next post, after having corrected a few errata. I am, dear Sir,

Your most humble servant,

B. FRANKLIN.

P. S. Mr. Martin is dead.

1

FROM CADWALLADER COLDEN TO B. FRANKLIN.

Concerning Theories of Light.

DEAR SIR,

Coldenham, 20 May, 1752.

I received yours of the 23d of April,* as I was going

on board the sloop, on my return home from New York, and could not take the pleasure of reading it before I left that place.

One so much conversant in examining any particular phenomenon, or various phenomena issuing from the same cause, must on every occasion give the pleasure of learning something new to those less conversant in them, as often as the former is pleased to answer any objections made by the latter, or explain the diversities which attend the same phenomenon in different cases or appearances.

* See this letter in Vol. V. p. 283.

Your conjecture of the electric fluid's taking place in the superior regions of the atmosphere pleases my fancy, as it in some measure confirms what I have advanced in the treatise now in the press, viz. that all the planets, in a greater or less degree, emit light, and indeed, I think, all bodies do. It does not follow, that, because we do not see the light, none is emitted. Some men can see where others are entirely in the dark; and some animals, as owls, bats, &c., see in the dark, and cannot bear so great a degree of light as is necessary for our perceptions.

When you shall see that tract you will have opportunity of judging of the validity of the reasons I advance for an opinion, that light is a substance or being essentially distinct from what we commonly call matter or body; that they have nothing in common between them, except that we consider or conceive both as consisting of quantity, that is, that in the same space there may be a greater or less quantity of either, and that a certain quantity of either may be confined within certain bounds, and consequently have some shape or form. Light has no power of attraction, though it be attracted by resisting matter. The vibrations of a fluid will in no manner explain the phenomena of light, as is very expressly pointed out in Sir Isaac Newton's Optics; for example, "Light proceeds always in straight lines, unless diverted by some other thing; for this reason, any opaque body placed between the eye and a luminous body intercepts all the light; but it does not intercept the sound coming from a sonorous body, because sound is conveyed by the vibration of a fluid medium, not by any emission of particles from the sounding body." Again, the separation of the distinct parts of light, which excite in us the different and distinct sensations of colors, and which, once separated,

always remain the same, proves that these sensations cannot be produced by the vibrations of any medium supposed to convey the action of light from the luminous body. I am persuaded, that a careful attention to the phenomena in Sir Isaac's Optics, and to his reflections on them, will remove all doubt on this head.

On this occasion I think it proper to observe to you, that, in the treatise before mentioned, what Sir Isaac has proved is generally taken for granted and supposed to be known.

It may be proper likewise to observe to you, that pure light, without any other mixture, makes no impression on any other sense except the sight; that the sense of heat arises from the action of light united with the action of some resisting matter. So, likewise, we have no idea of fire without the union of resisting matter with light.

In considering all quantities or degrees of action or force, whether in ascending or descending, whether in considering them as continually increasing or as continually decreasing, the ratio of comparison must at last come to that of infinity. We have no idea of the absolute force of any thing, only of its comparative force or ratio of its force to that of some other thing. The force of different quantities of light does not arise from the different velocities, (for I suppose all light always moves in the same ratio of velocity,) but from the greater quantity or density of light in the same space.

If the emission of light be not continued but by distinct vibrations or pulses, and an infinitely thin surface of light be thrown off in any finite part of time, suppose in a fifth, then there cannot be any finite or determinable diminution of the light of the sun, or of the diameter of the light in the sun, in any finite time. If the intervals of the vibrations or emissions of infinitely

thin surfaces of light be in an infinitely small part of time, it may take a hundred or a thousand years to diminish the sun's diameter one inch. You will find something of these abstract speculations in the treatise I mention.

I have much reason to apprehend the errors of the press, when I reflect on the manner in which the Indian History has been printed, with such gross errors in things obvious to the meanest understanding. Mr. Dodsley promised to get some person of learning to correct the press. Perhaps the difficulty he meets with in this is the reason that the impression was not completed in the beginning of March, though begun in December.

I shall be exceedingly disappointed if it do not meet with censure. I have laid my account with it, not only with unjust and injurious censure, but that many errors may truly be discovered, and that it will require much correction. It is impossible to avoid errors in things of this nature, more especially in a path not trod in before, and where I had no one to assist me to review and examine the work, a difficulty an author cannot labor under in England.

I have received a copy of the translation of my first piece into High Dutch, with animadversions on it at the end of it, printed at Hamburg and Leipsic, in 1748; but I do not understand one word of them. I find my name often in company with those of very great men; Newton, Leibnitz, and Wolfius. Leibnitz's Monades offers mankind a new doctrine, which perhaps you may have seen, and is of great repute in Germany. The animadversions end, "Magnis lumen excidet au sis," which, being in Latin, I understood.

The person in the Boston paper, who wants a fuller description of the poke-weed or phytolacca, than that