The general history of the air designed and begun by the Honble. Robert Boyle ...

TITLE VIII.

Of Aqueous Particles in the Air, and of the Moisture and Driness of the Air.

I Shall not here determine whether in all the Instances that are referr'd to this Title, the Phenomena be produced by the meer Moisture of the Air as such, or by some other Agents, whose Corpuscles are accom∣panied and assisted by the moist Air as a Vehicle and a concurrent Cause. But without nicely distinguishing the Grounds of particular Operations, we shall refer the Phenomena in general to the Moisture of the Air, (or moist Air) that Quality being the most obvious to be observ'd in these Phenomena; in the Production of some of which it seems either the only, or the main Cause, in others an assistant Cause, and in all a not use∣less Concomitant.

The Account upon which a Body is dry, being usu∣ally but this, that the Pores intercepted between its more stable Parts, are not fill'd with any visible Liquor, it is not to be expected that a Quality so near of kin to a Privation, should furnish much to our present histori∣cal Notes: But yet Driness may sometimes have a not∣inconsiderable Interest in the Changes of a Body, and that upon differing Scores, whereof I take these two to be the chief. 1st. As the Body by Exsiccation is de∣prived of those liquid and exhalable Parts that were be∣fore harbour'd in its Pores, and were perhaps the Prin∣ciple of divers Operations ascribed to it. And, 2dly. As

these Evaporable Parts by their Recess may occasion a Change of Texture in the Body, especially in regard of the Pores, whose Bigness, Figure, and perhaps Positi∣on, being alter'd, the Body by this Change of Texture acquires a Disposition to act, and be acted on, in seve∣ral Cases, otherwise than formerly.

Sometimes when the Weather began to be overcast, the Hygroscope did not sensibly appear to grow heavier, and sometimes it would preponderate when I took no∣tice of no Vapours to make it do so: and though these things happen'd but seldom, in respect of the ordinary Changes of the Hygroscope according to those of the Weather; yet they made me suspect that sometimes the Clouds may consist of other Steams than Aqueous, or that there may be some Exhalations that may have a peculiar Congruity with the Pores of the Hygroscope, and whose Nature may be such as to the Power of dry∣ing the Hygroscope, that upon these or some other, yet unheeded Accounts, the Steams that are sometimes diffused in the Air, may controul the usual and regular Causes of increasing or lessening the Gravity of the Hy∣groscope. And this Suspicion was the stronger, because having made Hygroscopes with Powder and Salt, and also with the Saw-dust of Wainscot, hung at nice Scales in very thin open Glasses, purposely blown for Lightness sake at the Flame of a Lamp, though they usually acquired and lost Weight, as the Weather grew moister or drier, yet sometimes they did not.

At half of an Hour after nine a Clock at Night, I look'd upon the Half Hundred Weight that hung at the bottom of the Rope, the Weather being then fair, and a Mark being put at that part of the erected Board where the bottom of the Weight touch'd, I perceiv'd the Sky a while after to grow cloudy and overcast, but without

Rain; wherefore going to visit the Weight again, I found it to be risen ¼ of an Inch or more; and looking on my Watch, perceiv'd there had pass'd an Hour and a Quarter since the Mark was made.

This Morning I came again to look upon the Weight between eight and nine of the Clock, and found it raised above the newly mentioned Mark, made last Night about one Inch, (for 'twas about 9/10 of an Inch.) This Day the Weather being fair and windy, the Weight was fallen by ten at Night about six Inches beneath its Station, at which I found it when I look'd on it in the Morning.

Being not well yester-night, the Weight was observ'd at Bed-time, by two of my Servants, and it then rested at the 11th of the erected Bound. This Morning about eight of the Clock, I visited it my self, and found it to be risen about ⅛ of an Inch above the eighth Inch, the Morning being cloudy, though the Morning very dry and dusty. The Weather growing more overcast, with∣in somewhat less than an Hour after, I visited the Weight again, some scatter'd Drops of Rain then be∣ginning to fall, and found it to be risen about half an Inch above the newly mention'd eighth Mark.

I look'd when I was ready to go to Bed upon the su∣spended Weight of 56 Pound, and mark'd how low it reach'd upon the divided Board; and a great part of the Night having been rainy, I look'd again when I was dress'd in the Morning, which was about half an Hour after eight a Clock, and I found the Cord so shrunk, that the Weight was raised above five Inches higher than I left it the Night before; but the Day recovering dry and windy, and sometimes warm, the Rope was so stretch'd, that at Night the Weight sunk a good way beneath all the Marks. N. B. The Rope near the Weight

was in Diameter •• of an Inch, and four decimal Parts of a tenth.

We took a Rope of near three Foot and an half in length from the Point of Appension, and somewhat less than •• (Inch) in Diameter; this we suffer'd to be stretch'd for some Days by a Weight of Lead with an Iron Ring or Ansula, weighing a Quarter of an Hun∣dred, according to the great Hundred, which is five score and twelve: and then placing a flat Board under it so, that the Weight just rested upon it, we had the Rope well wetted over them with a Spunge dip'd in Water, and so often applied to it, that the Liquor might be tho∣rowly soak'd into the Pores of the Rope, which at first seem'd thereby a little stretch'd, rather than shorten'd; but after an Hour or two it began to shrink, so that we could make the Weight swinge like a Pendulum over the Piece of Board it lean'd upon before. But after∣wards the same Day the Weight stretch'd out the Rope again as much as formerly.

'Tis observable, that though Morocco be an Inland-Town, and the Soil of those Parts be usually dry, if not parched; yet Doctor D. who was lately there, inform∣ed me, that about Morocco, notwithstanding the violent Heats he felt in the Day-time, he observed the Noctur∣nal Air to be very damp, so as to make the Clothes he put off at Night exceeding moist, and unfit to be worn without airing the next Morning. He added, That though the Air was very piercing, and manifested it self to be so by many other Signs, yet it would not make his Knife rust in his Pocket, or his Sword in the Scabbard, though it would quickly produce a Rust in Instruments of that Metal exposed naked to it.

Air too moist cannot be wholesome. The Air in our Parts, viz. about Oakly in Buckingham-shire, though a

high Country, is, as I said before, between Michaelmas and Alhallontide very moist, especially in rainy Wea∣ther, and upon a Thaw, insomuch that Wainscots, Stair-cases and Pictures will stand all of a Water, and after run down in great Drops; and at Brill, upon that high Hill, 'tis in divers Houses worse than in the Val∣ley, insomuch that the Stair-cases, especially if laid in Oil, will run down with Water: the North and North-East side of our Houses are observed to be moister, insomuch that the Furniture will rot, if Fires be not made some∣times in the Rooms, and the things aired: This is observ'd to be the most aguish Season of the Year. Mr. J. T.

As in another Experiment wetried, whether or no the Removal of the Air out of the Receiver would much alter the Temperature of the included Medium or Space, as to Heat and Cold: so we indeavour'd to discover, whe∣ther the Alteration would be notable, as to Driness and Moisture. To this purpose we did indeed wish for such a Hygroscope (or Instrument wherewith to mea∣sure the Moisture and Driness of the Air) as we used many Years ago, and since found well described by the industrious Kircher, in a Place of his Ars magnetica, to which I therefore refer your Lordship. But in regard that to this Instrument there is requisite the Beard of a wild Oat seasonably gather'd, which we could not then procure; we recall'd to Mind another Hygroscope, which, though it discover not such small Mutations as the former, we thought might be usefully enough sub∣sticuted instead of it.

Of this Hygroscrope, having particularly described it in another Paper, we shall now only say in a word, that 'tis made by fastning to the upper End of a Piece of Gut-string, or great Lutestring, a very light Index, and strongly fastning the lower end of the same String

to the bottom of a Box, or other convenient Frame, the Circumference of whose upper Part may be at pleasure divided into Degrees or other Partitions, upon which the Index may move to and fro. For the Instrument being thus made, when the Air grows moister, the Va∣pours insinuating themselves into the Pores of the Fila∣ments that compose the String, do somewhat shorten it; and thereby those Filaments being altered in point of Contortion, the Index that is fastned to them turns one way: and upon the recess of those Vapours, or of others of like nature, the String comes to be wreath'd, and consequently the Index to be moved another way. So that in a String of about three Inches long, the Point of the Index will be oftentimes made to change its Place very notably, by such a mutation of the Air, as to Dri∣ness and Moisture, as was to be met with in the Mor∣ning and at Noon of the same Day, tho such a Change did not always need either Rain, Clouds or Mists, or the absence of them, to make it notable.

We took then one of these Hygroscopes, and con∣veyed it into a small Receiver, that the removal of the Air being sudden, the Change of Temperature (if any should happen) in the exhausted Cavity, might be the more sudden and conspicuous. But we found not that the emptying of the Receiver made the Index sensibly change place. And though this Experiment were care∣fully made, yet for the greater Security we repeated it once more; and neither then perceiving the Index to remove, we kept the Receiver exhausted for a pretty while, lest there should be some more time requi∣site to the Operation of the Medium upon the Instru∣ment. But neither did this Trial produce any sensible Alteration of the Index; but after the Key was turned, and Access was thereby given to the excluded Air, tho

the Cover were still kept on, we found that then with∣in some Hours, the Index was considerably removed. So that as far as these Experiments informed us, the Ether or subtile Matter that succeeds in the place desert∣ed by the Air, if that Place be not left void; and conse∣quently the thinner and more fluid part of the Atmo∣sphere (in which the Corpuscles, that may be more properly called Aerial, swim) seems in its own nature to be very sensibly, neither cold, or hot, or dry, or moist. I said, as far as these Experiments, I mean those we made in this Engine with the Thermoscope and Hy∣groscope, inform us: because this Conjecture (for I dare yet call it no more) may be examined divers other ways, whose Events may either confirm, or oppose, or limit it. In the mean time I could wish, that if your Lordship had one of Kircher's Hygroscopes at hand, you would frequently and carefully try the last-recited Ex∣periment with it; because I have found, that if such a Hygroscope be very well made, 'tis admirable, as well as pleasant, to see how small a Mutation of the neigh∣bouring Air it will take notice of. But I thought fit to desire to have it frequently tried, because Care must be taken that such Motions of the Index be not mistaken for the Effects of the altered Temper of the Medium in the Receiver, which may in some Cases proceed from those Steams of the Oil and Water, which we elsewhere mention, that we now and then, tho but seldom, ob∣served to get out of the Cylinder into the Receiver, and play up and down there.

Notes

• A Transcript of an Observation made at Stan∣ton.
• Experiment I.
• Experiment II.
• Experiment III.