Lettre 305 : Thomas Molyneux à Pierre Bayle

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Leyden July the 27 th [1684]

Worthy S[i]r

I find1 by some passages in your Nouvelles de la republique des lettres, that you understand the English tounge2, and have correspondance with some of that nation, therefore I chose rather to make use of my owne mother speech in letter to you, than to venture at French ; of which language I can’t pretend to be so great a master as to attempt to wright in it, without at the same time I would expose my weakness, which certainly when I can help would be a great folly, especialy before so disarming a judg[e] and so nice a critick as yourself.

When first I met with your journals I was very much pleas’d to see that one had taken upon him this designe in Holland, which is so universaly embracèd in most of the civilis’d countrys in Europe ; but when I had read them I was abundantly more pleas’d, to find that one so understanding, so impartial, and so well skil’d in all parts of learning, had undertaken the designe, who was so able to performe it both much to his owne honor and the satisfaction of all readers whatsoever ; who certainly must be much gratifi’d and delighted to meet with so curious observations in natural philosophy, and such full, accurate, and judicious accounts both of authors and their books : whith thees [ sic] certainly no man that has the least taste of learning can be displeas’d, and as to your natural observatins if they dissatisfy, it must be only on the account they are so few as not to stay the appetite of an age that so eagerly persues or devoures[,] I may say[,] this part of learning[,] natural philosophy.

Hence it is that observations of this kind take up so great a part of the Journal des sçavans, the English Transactions3, the Ephemerides Germanorum 4, the Acta danica 5, et lipsiaca 6, with those several publish’d in Italy, at Rome, Florence, Venice, etc7. (which Italien [ sic] journals being so rarely to be mett with in thees countrys, I imagine you would far more oblige the learned of thees parts[,] to take now and then extracts out of them, rather then out of the Journal des sçavans or any of the rest that are so common here) all thees I say are full of remarks in natural philosophy, and are examples S[i]r I think worthy to be follow’d by you in this particular, and in this allone, for in all other things, as your impartial and accurate accounts of books etc.[,] it is manifest to any judicious reader you go far beyond them.

And because I would not only give you my bare advice in this matter (which I hope [Si]r you’l excuse seeing it comes from a modest desire both of yours and the publick good,) I have flung in my mite to set forward the designe which if you think worthy of a place in your Nouvelles you may encourage for the future to send you something that perhaps may better deserve it.

In the meane time I remain S[i]r your most humble servant to command (tho’ unknowne)
Tho. Molyneux

turne over /

Concerning the dissolution of heavy bodys in menstruums8

There is scarce a more common operation in chemistry, and that’s oftner made use of then the dissolving of hard bodys by such and such menstruums ; which for the most part if not constantly are lighter in equal quantitys then the body they dissolve ; and yet the final subtile parts of thees heavy bodys when they have been minut[e]ly divided by the accute and penetrating parts of a far lighter menstruum, freely float, tho not to be discern’d by sconce, and swim up and down in it which is quite contrary to the laws of hydrostaticks.

As for example, mercury or quicksilver, which is above ten times as heavy quantity for quantity as aqua fortis or spirit of niter, yet it will presently be dissolv’d in either of them (if they be strong and well prepar’d) so that the spirit of niter shall remain clear and transparent and nothing of the mercury shall appear. Now we must necessarily conclude that it is only divided into very minute parts, so small as not to hinder the passage of the light, nor to be discern’d by our eye, and thees are cept up floating and swimming in the liquor.

But now if we consider the true cause in general of all things sincking or swimming in fluids it will be so far from explaining this phenomenon that it will seem to be quite contrary and wholy irreconsilable with it.

For thees are lay’d down as maxims and undeniable truths in hydrostaticks : that a solid body, in a fluid quantity for quantity lighter then itself, must sinck ; if the fluid be heavier, it must necessarily swim atop whereas if they be both of equal weight, the solid will float as we say, that is neither sinck nor swim.

But here we have an instance of a body ten times at least as heavy as the fluid yet for all that supported by it and freely swimming in it ; and tho the mercury be divided into very minute parts, yet certainly the smalest particle of it bears still the same unequal proportion in weight to a particle of spirit of niter of the same biggnes, as an intire inchecube of one dos to an inchecube of the other.

Yet notwithstanding we are not to deny the truth of those undoupted propositions of hydrostaticks so fully establish’d and demonstrated both by reason and experiment ; but are to enquire whether or no there is not something more to be consider’d in this appeerance besides the bare causes of sincking and swimming ; and if so we shall then find that it no more contradicts those undoupted laws before mention’d, then dust’s fliing in the air, when it is violently mov’d, tho it be far heavier than it, or gravell swimming in water when it is strongly agitated or stir’d about.

For in our present case, tho the dissolvent and its parts lyes indeed quiet as to all outward appeerance ; yet it is allow’d and known that the essence of all fluids consists in the brisk motion of those minute parts that compose them. Now • the menstruum has divided the mercury into such very small particles that alltho they be heavy for their bulk, yet they become so very minute that the loa[d] force imaginable moves them and they are capable of having motion [im]pres’d in them by the very moving parts of the fluid ; so that by this means they are kept up floating and swimming in’t : whereas were they so large as not to be work’d upon by this internal motion of the parts of the liquor, which can have no effect on greater bodys, they would certainly according to the laws [of] hydrostaticks sinck to the bottom.

And this I take to be the cause of this odd appeerance, why this as well as all other heavy bodys swim in their menstruums when dissolv’d ; and a manifest argument to prove, that the parts of all fluids are in perpetual motion. And so much for this time shall suffice.

If S[i]r you’l trouble yourself to send me an answer you may direct it for me to be left at the English ordinary at the signe of the Blen Clock by Peters Kerk in Leyden9.


• Aen Mr Ferrand/ Koopman/ tot Rotterdam/ voor den autheur van [der] Nouvelles de la republique des lettres/ het Port betade


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