Excerpt:

ILLUSTRIOUS Sir, and most worthy friend,—SO painful to me was the separation from you the other day after our meeting in your retreat at Rhijnsburg, that it is my first endeavour, now that I am returned to England, to renew, as far as is possible by correspondence, my intercourse with you. Solid learning, conjoined with courtesy and refinement of manners (wherewith both nature and art have most amply endowed you), carries with it such charms as to command the love of every honourable and liberally-educated man.

Let us then, most excellent sir, join hands in sincere friendship, and let us foster the feeling with every zealous endeavour and kind office in our power. Whatever my poor means can furnish I beg you to look on as your own. Allow me in return to claim a share in the riches of your talents, as I may do without inflicting any loss on yourself.

We conversed at Rhijnsburg of God, of extension, of infinite thought, of the differences and agreements between these, of the nature of the connection between the human soul and body, and further, of the principles of the Cartesian and Baconian philosophies.

But, as we then spoke of these great questions merely cursorily and by the way, and as my mind has been not a little tormented with them since, I will appeal to the rights of our newly cemented friendship, and most affectionately beg you to give me at somewhat greater length your opinion on the subjects I have mentioned.

On two points especially I ask for enlightenment, if I may presume so far; first: In what do you place the true distinction between thought and matter? secondly: What do you consider to be the chief defects in the Cartesian and Baconian philosophies, and how do you think they might best be removed, and something more sound substituted?

The more freely you write to me on these and similar subjects, the more closely will you tie the bonds of our friendship, and the stricter will be the obligation laid on me to repay you, as far as possible, with similar services.

There is at present in the press a collection of physiological discourses written by an Englishman of noble family and distinguished learning.

They treat of the nature and elasticity of the air, as proved by forty-three experiments; also of its fluidity, solidity, and other analogous matters.

As soon as the work is published, I shall make a point of sending it to you by any friend who may be crossing the sea.

Meanwhile, farewell, and remember your friend, who is Yours, in all affection and zeal,

HENRY OLDENBURG.

London, 12/26 Aug., 1661.

***************

Illustrious Sir,—How pleasant your friendship is to me, you may yourself judge, if your modesty will allow you to reflect on the abundance of your own excellences. Indeed the thought of these makes me seem not a little bold in entering into such a compact, the more so when I consider that between friends all things, and especially things spiritual, ought to be in common. However, this must lie at the charge of your modesty and kindness rather than of myself. You have been willing to lower yourself through the former and to fill me with the abundance of the latter, till I am no longer afraid to accept the close friendship, which you hold out to me, and which you deign to ask of me in return; no effort on my part shall be spared to render it lasting.

As for my mental endowments, such as they are, I would willingly allow you to share them, even though I knew it would be to my own great hindrance. But this is not meant as an excuse for denying to you what you ask by the rights of friendship. I will therefore endeavour to explain my opinions on the topics you touched on; though I scarcely hope, unless your kindness intervene, that 1 shall thus draw the bonds of our friendship closer.

I will then begin by speaking briefly of God, Whom I define as a Being consisting in infinite attributes, whereof each is infinite or supremely perfect after its kind. You must observe that by attribute I mean every thing,

which is conceived through itself and in itself, so that the conception of it does not involve the conception of anything else. For instance, extension is conceived through itself and in itself, but motion is not. The latter is conceived through something else, for the conception of it implies extension.

That the definition above given of God is true appears from the fact, that by God we mean a Being supremely perfect and absolutely infinite. That such a Being exists may easily be proved from the definition; but as this is not the place for such proof, I will pass it over. What I am bound here to prove, in order to satisfy the first inquiry of my distinguished questioner, are the following consequences; first, that in the universe there cannot exist two substances without their differing utterly in essence; secondly, that substance cannot be produced or created—existence pertains to its actual essence; thirdly, that all substance must be infinite or supremely perfect after its kind.