For Mr John Locke at

Sir Francis Marsham’s

at Oates near Bishop Stafford




I. Newton 30 Jan [1691].



Your referring to answer my letter is what you need not make an apology for because I use to be guilty of the same fault as often as I have nothing of moment to write & therefore cannot in justice complain. If the scheme you have laid of managing the [the word looked like “Contreuleurs”] the place M. will not give you trouble of too large a letter, you will oblige me by it. I thankyou heartily for being so mindful of me & ready to assist me with your interest. Concerning the Ancient of Days, DAN. 7, there seems to be a mistake either in my last letter, or in yours because you wrote in your former letter the Ancient of Days in Christ, and in my last I either did or should have asked how you knew that. But these discourses may be done with freedom at one more meeting. I am indebted to my solicitor Mr Sharkey. If you please to let [him] have your opinion read him, I will send it with a letter by the courier. My Lady Marsham & you have done me much honour in looking into my book, & I am very glad to have approbation of such judicious persons.


The observation you make in Mr Boyle’s book of colours I once made upon myself with the hazard of my eyes... The manner was this. I looked a very little while upon the sun in a looking glass with my right eye & then turned my eyes into a dark corner of my chamber and then winked to observe the impression made & the circles of colours which encompassed it & how the decayed by degrees & at last vanished. This I repeated a second & a third time. At the third time when the phantasm of light & colours about it were almost vanished, intending my fancy upon them to see their last I found to my amazement that they began to return & by little & little to become as lively & vivid as when I had merely looked upon the sun.  But when I ceased to [this word looks like “intend”] my phansy upon them they vanished again. After this I found that as often as I went into the dark & intended my mind upon them, as when a man looks earnestly to see anything which is difficult to be seen, I could make the phantasm return without any looking any more upon the sun. And the oftener I made it return, the more easily I could make it return again, & at length by repeating this without looking any more upon the sun I made an impression on my eye. That I looked upon the clouds or a book or any bright object I saw upon it a round bright spot of light like the sun. And which is still stranger, though I looked upon the sun with my right eye only and not with my left eye, yet my phansy began to make the impression upon my left eye as well as upon my right. For if I shut my eye and looked upon a book I could with my right if I did but intend my phansy a little while upon it; but by repeating this, appeared every time more easily. And now in a few hours time I had brought my eyes to such a pass that I could look upon no bright object with either eye but I saw before me, so that I dared neither write nor read but to recover the use of my eyes shut myself up in my chamber made dark for three days together & used all means to divert my imagination from the sun. For if I thought upon [the word looks like “him”] I presently saw this picture though I was in the dark. But… by keeping in the dark and employing my mind about other things I began in three or four days longer to look upon bright objects recovered them pretty well, though not so well but for some months after the spectrum of the sun began to return as often as I began to meditate upon the phenomenon, [this word looks like “some”] though I lay in bed at midnight with my curtains drawn. But now I have been very well for many years, though I am apt to think that if I dared venture my eyes I could still make the phantasm return by the power of my phansy. This story I tell you to let you understand that if the observation related by Mr Boyle, the man’s phansy probably concurred with the impression made by the sun’s light to produce that phantasm of the sun, which he constantly saw in bright objects. And so your question the cause of this phantasm involves another about the power of phansy which I must confess is hard to it too hard a knot for me to untie. To place this effect in a constant motion is hard because the sun ought then appear perpetually. It seems rather to in a depression of the [the word looks like “sensorus” perhaps to mean “senses”?] to move the imagination strongly & to be easily moved both by the imagination & by the light as often as bright objects are looked upon.


If the papers you mention come not out I will tell you at our next meeting what shall be done with them.


My humble service to Sir Francis, My Lady and Mrs Cudsworth.

I am

Your most humble servant,

Is Newton.


Letter from Isaac Newton to John Locke, dated the 30 th January 1691.