Chapter 8

Of Air

AIR is (by the Antients) an Element most Humid, and Warm its motion is upwards; its place between fire, and Water; and this divided into 3 regions.

1. The lower region which begings at the Earth or Water, and reaches up to the place of the Cloudes, because so fare the beams of the Sun are more Strongly reflected from the Earth whose steame they cary with them to be the matter of the Clouds.

2. The Middle region which from the Extent of the lower region reacheth to the top of the Cloudes: this is said to be the coldest of the 3 for a 2 fold cause privative, and positive.

1. Privative because it is so far from the fountain of heat that many rayes springing from that body do not reach it, and So far on the other side from the Earth that the reflected rayes [22] of the Earth do not assend unto it.

2. Positive and that (still according to the Antients)


by accident

1. Directly, the cold Vapours that are by heat lifted up; but then returning to their native cold they cool, and Chill the Air that is mingled with them.

2. By Accident, the Antiparistasis, (a [Greek] compound word, hansomly Signifying, natures Strugle, or contranitence against what dos oppose it;) for as nature ordinarily opperates according to the Utmost of its power, So does it much more, and Especially when it is to conquer a difficulty. Thus Fire beseiged with cold in frosty weather Scorches more vehemently having its heat thereby intended: and [by] like reason the middle region of the Air being beset on both sides (both above, and below) by those warmer ones, has its cold between them intended also. The Vapours, (I suppose they mean those which are naturally cold) have their cold strengthened; as the hot vapours also by this neighbouring cold are heightened somtimes even to a flame. And from these reluctancyes is the Generation of meteors in this part of the Air (of which after) Whether the Air it self have any native cold may well be doubted as contrary to their [own] deffinition of Air.1 These 2 Regions togather are called the Earth[s] atmosphere whose extent is variously assigned: Some say tis 3 miles of perpendicular height from the Earths Surface, some 4, some 7, Some more; [Tis not far above the Topes of higher mountains, Some Say;] It may not be So high, Say others; Olympus is said to have its name from (ὁλος λαμπρος) wholly clear without clouds, they mounting not so high. A Part of the Alps near Padua is said to have a hill where men ascending, have Gone from great heat at bottom, through Snow in the middle to dry land at the top, where no rain nor dew comes, and therefore no Vegitable there to be seen. but below them they have observed thundring lightening, and great Stormes whereas themselves have not felt the least motion of the Air. And the like (in the Phylosophycall transactions) is said of the pike of a Teneriff.2

3. The Highest region of the Air is from the hig[h]est of the Cloudes, to the Element of fire (as they speak according to the old hypothysis) which is so tenuious and thin that it is unapt for men to breath in; and therefore those assenders to the tops of those highest hills (before mentioned) ware forced to carry moisted Spunges in their teath, that thereby the Air might be qualifyed to the necessity of their natures. This region is said to keep its quantity of Extent whereas the other 2 do vary it; for in Summer the lower is biger, and in the winter less giving to or taking from the middle according to the strength, or weakness of the [Suns], reflexion, (or rather according to the more direct or oblique reflexion of the sunbeams;) for direct reflexion riseth high, as [is playn] in a boyes ball thrown directly against the ground (the Angle of incidence and the Angle of reflexion being the same) See this in the diagram; for Suppose the Discendent ray (or ball,) passeth in the line (aa) it will rise as high as the pricked line (ad.) (thus in the summer) but if it discend by the line (b.b.) it will rise no higher than the pricked line (b.c.) thus in the winter this determines the Quantity of the lower region which in the Summer is as high as (a.d.) but in the Winter only as (b.c.)

Now to Explain why the middle region is most cold; you may Suppose that some rayes of the Sun do not reach home to the Earth (a.b.) but only So far as the pricked line (a.d) Other[s] again come down and smite the Earth (a.b.) and rebound as farr as the line (b.c.) Tis manifest the num[b]er of rayes are double above (a.d.) and below (b.c.) [to what they are between (d. and c.)] therefore the upper region (1.) is hotter by the double number of direct beams, and the lower (3.) by half direct, and half reflex, but the middle (2.) cold because it hath but half the number of the other.

Extreams are hot but cold the middle is

By Vapours, rayes want, Antiperisthesis.

The Affections of air are absolute or respective.

1. Absolute affections such as appertain to it absolutely considered without respect to the mixtures in the Atmosphere, these are 3, Fluidity, Elasticity, and Weight.

1. Fluidity or Easy Seperation of its parts which have no cohæsion, at least [much] less than water (as we before noted) and hence that aptness to receive into it Heterogeneous bodyes, Such as rayes of light; Steames of the Atmosphere; and Evaporations from particular bodyes that give a scent pleasing or offencive.

2. Elasticity or Springiness cal’d power Elastick, or restitutive, whence an apt-[23]ness to return to its due Extension, when either the parts are pressed togather, or Stretched assunder beyond their natural State. Illustrated by a pound of wool which is capable of being thrust into a Quart pot; but when freed of the compression, will of its self expaciate to its former bulck: and (on the other hand) any Curled hair of wool, may be drawn out to a greater length, than Usually it stands at; which when discharged of the force will shrink again into its former posture. So it is in the body of Air; this compression of air is call’d condensation, because then it has more of matter in less space; and its contrary distension, is cal’d Rarefaction because it has less of the matter in a greater space; But what fills the Vacuity[es] between the parts in Rarefaction, in such cases where no sensible suply is to be perceived is a great Question; as for Instance; Suppose in the Thermometer, or Water-Weather [Glass] the Water stands at (c.) the warmth of the air, or ones hand laid at top will presently bring it down to (d.) hereby the Air in the ball (A.) is rarifyed; now are the parts of it at greater distance each from the other, what is between them must be either a vacuum, or it is Ætherial, [or] fiery matter, that can Easyly permeate the pores, of the Glass to avoid a Vacuum; and so again when by Cold the Water assends to (b.) the matter that filled [the] Spaces must find the way out, as it found the way in, or there will be in the condensation of that air in the ball, a penetration of dimensions; which is impossible I rather therefore Chuse the latter; namly the permeating Matter, because nature abhors a Vacuum: The force of this sp[r]ing of the Air is great, as appears in Wind Guns, and Artificial fountains, formed on this foundation; as also the lifting of weights by an half blown bladder in the Evacuated vessell of the Air pump.

3. Weight or tendency to the Center of the Terraqueous Globe, of this it must have some small proportion, else the Upper region at least would be diffused [and] lost in the vast Æther, which lies between us and the other planets; or else the steams of the Atmosphere would hardly be held up by the reflecting sun beams; which also could not well return to their fountain, the Sun, unless chrushed up through the Air, (as cork is out of water) till they come to the Surface thereof and into the Æther where they shall meat with no resistance, and thus much of absolute affections of Air.

2. Respective are such as are ascribed to it as mingled with the Terraqueous Steame of the Atmosphere. This mixture (as before Shewn) is by the reflecting beams of the Sun carrying [up] somthing of what they strick upon; (as a boyes ball licks up Moisture or dust according to the place it falls upon) now these particles carryed up are minute bodyes keeping the Qualities of their originals. And from these it is that the 2 lower regions of the Air are denominated not only of the first Qualities, Hot, Dry, Cold, or Moist; but have ascribed 2 notable attributes to them now to be Spoaken of Greater weight and aptness for breathing.

1. Greater weight, than that which is natural and absolute (before mentioned) This is both proved, and measured by the [Torricellian] Experiment to be Equiponderant in a Cilinder of Glass, (say of an Inch or half inch Diamiter) (or any Dimension) [to] the like Cilinder of Quicksilver ([or] Mercury, ☿) 29 Inches long; and of Water 32 foot; thus suppose a hollow Cilender of Glass (say of ½ Inch diamiter and 40 Inches long) close at the one End (c.) and open at the other, fill it with Mercury (☿) and Stop it at the open end with your finger then invert the pipe that the close end (c.) be upwards, [Drown] your finger, and the open End in mercury (8) contained in an open glass or Wooden vessel (a.) remove your finger and the (☿) in pipe that was before full up to (c.) or 40 Inches from the Stagnant (☿) in the vessel (a.) will presently fall down and hang at (b) 29 Inches from the surface (a.) The reason is (say they) because a pillar of the Atmosphere of the Same diamiter with the (☿) reatching from the top thereof to the Surface of the vessled (☿) in (a.) is Equipoise to the little pillar of (☿) 29 Inches (more or less) which is Sustained in the Glass pipe; and because the Close End at the top (c.) bears off the pressure of the atmosphere from the (☿) in the pipe and it falls [without] impediment on the ☿ in the vessel; therefore it must press, or Keep up so much mercury in the pipe as will Equipoise the like pillar through out the whole atmosphere; this weight of the Atmospher varyes in Several times, and places. Therefore the Cilinder of mercury in the pipe is shorter on the top of an high mountain than in the valley; because the like Cilinder of [24] the Atmosphere is longer in the whole perpendicular height, of the Mountain, and therefore must weigh more, and have more mercury in the pipe to counterpoise it. Dr. Power (Page 104.)3 notes that [Pascalius] in a mountain of 500 Perch high found the Difference 3 Inches whence he Sugests that by the rule of proportion we may find out the height of the Atmosphere, thus;

Height in the tube 3 Inches

Height of the hill 500 perches

Height in the Tube 29 Inches

Height of the atmosphere 4833 perches

i.e. 15½ miles.

It Varies also in the same place so [as] the Atmosphere presses upon the mercury in the Cilinder more, or less in the compas of about 6 Inches, according as the Steams are more or less assending or discending in the Air. And thus are made Barometers or s Weather Glasses now of common Use.

2. Aptness, yea necessity for breathing is ascribed to the Atmosphere, and its colder parts for pure air is unapt for respiration (as is before noted). This is a perpetual Ambient Ingredient [into] our bodyes, and is always [mixing] with our animall Spirits, not only (though cheifly) by breathing; but permeating the pores of the whole body; and from hence arises the Distinction, of wholsom, and unwholsome, Sweet, and corrupted Air; for if it be Impregnated with benign [and] balsamick particles, it Cherrishes, maintains, and restores health. But (on the other hand) if the Steams are fœted, and poysonous, or otherwise Maligne, they distroy the Health, and Endainger the life. Hence fires in the streats of a Citty, Shooting of Great Guns, ringing of bels are accounted profitable in the time of pestilence; as also the natural helps of frost, and wind, Rain, etc: because these in some measure beat down, and dissipate those Miasmas or corrupted Venemous steams that hover in the Air. Hence our care is (or should be) to mind well the place of our habitation, or Settlement that the Air thereof be Sutable to our bodyes by its agreable steames; Hence also tis that some persons in Cronical distempers are sent for their health to their native air, that is to the steames that formerly agreed with them.

[Respective attributes are greater weight,

Usefull for Respiration; when tis right.]