Oeuvres complètes. Tome VI. Correspondance 1666-1669

N^o 993^a.
R. Boyle à R. Moray.
Appendice au No. 993.
[mars 1662].

La lettre se trouve à Leiden, coll. Huygens.

I am sorry the arriuall of vnexpected company robs me of the time J design'd to answer that part of Monsieur Zulicum's letters which concern's me, as particularly as J intended. But not wholy to disobey you and him, J shall waue the solemne acknowledgment his aduantageous & obleiging character of my Scepticall Chymist, would exact of me if J had as much leisure as resentment. And J shall hasten to acquaint You in few words, that though J dare affirme nothing till J haue made further tryalls of the descent of water in the exhausted Receiuer; yet in the meane time J confess it seemes not improbable to me that the non descent of the water obseru'd by Monsieur Zulicum might proceed from this that the air was not sufficiently pumpt out. and on this occasion J cannot but recommend to him the making vse of a gage (if J may soe call itt) or stander or index within the Rec-

[p. 582]

ceiuer by which he may know how far it is euacuated & how will it keeps out ye air. sometimes we haue imployd a bladder with a very litle air in it whose neck being strongly tijd ye swelling of ye bladder in some measure discouer'd the degree of expansion of the air in the Receiuer. But this may be better done by a slender crooked glasse silld with water all except a small bubble of air of a known quantity, for by conuenient diuisions vpon the outsides of this glasse 't will be easy to see, to how many times its bulk (whether 50, 100, 150, or 200 times) the included Bubble is rarifyd. And by ye shrinking of this bubble both the leaking of ye vessell may be concluded & the quantity of the admitted air may be ghest at. A more particular description, J neither haue the leisure to set down, nor need to suggest to such a Person as Monsieur Zulicum. And one reason of my mentioning it here, is, that J suspect for want of such a gage he may haue thought his Receiuer better exhausted then indeed it was. for though he sayes that the engine held stanch for many houres yet that does necessarily inferre noe more then that noe new air got in. But not that the preexistent air was all drawne out: now in case the Receiuer were not sufficiently emptied the remaining air though little, may well, in a small glass, haue spring enough to keep ye water suspended in such short tubes as he made the tryalls in. For J remember that when we thought we had carefully enough emptied our Receiuer there remaind in the tube about an inch of Quicksiluer which you know answers to 14 inches of water. As for the Reason Monsieur Zulicum giues of the depression of ye water in the tube when that liquor was not first freed from air J think it very good, and it agrees very well with what J relate in the experiment concerning the measure of the airs expansion. That Phenomenon of the great bubbles rising noe higher with its lower surface then the leuell of the externall water, J should ascribe to the want of pressure in the water vnassisted by the air, but that J haue not you know his letter by me, and may mistake some circumstance. wherefore to comply with my hast I shall adde noe more, saue my humblest thanks to Monsieur Zulicum for ye great ciuility vouchsafd me in his letters; & shall deferre ye making further reflections on this subject till further tryall made either by him or me, for J am as well hopefull as willing to receiue instruction from such teachers as Experience and He.

These

For Sr. Robert Moray.