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they prove rich or poor in matter. But there is another class of things which we call pneumatical, or untangible; so that not being subject to the balance, no judgment can be formed of the distention or rarification of the matter they contain. Whence this affair requires another kind of interpretation. But first; the several species of pneumatical bodies are to be laid down; that they may be compared with each other. But as in the case of tangible bodies, we for a time postpone the consideration of the internal parts of the earth; so in the case of pneumatical bodies, we postpone for a time, those that are ethereal.

We range pneumatical bodies under three general classes; viz. .1. The imperfect; 2. the confined; and 3. the pure. 1. The imperfect are, fumes of all kinds, proceeding from different matters. These may stand in this order; 1. Volatile fumes that breathe out from metals and some other fossils; being, as their name imports, rather volatile than pneumatical; and very easily coagulated either by sublimation or precipitation. 2. Vaporous fumes, expiring from water and aqueous bodies. 3. Under the general name of fumes, we likewise include the expirations of dry bodies. 4. Exhalations proceeding from oily bodies. 5. Breaths afforded by bodies aqueous in their substance, but inflammable in

their spirit; as in wines, and other fermented spirituous liquors.

There is also another kind of fumes in which flame terminates; and such as expire only from inflammable bodies, consequent to the flame: and these we call after-fumes, or secondaryfumes. So that there can be no after-vapours, because aqueous bodies are uninflammable; but there may be after-fumes, in our particular sense, as also after-exhalations, after-breaths, and probably after-volatile parts in some bodies.

2. But confined pneumatical bodies are those found, not independent or free, but included in tangible bodies; and are what we commonly call spirits. These participate both of an aqueous and oily substance; and are nourished and fed thereby and being converted into a pneumatical substance, they constitute a body, as it were consisting of air and flame; and thence produce the strange effects of both*. These spirits, with regard to pneumatical bodies that are free and at large, nearly approach to the nature of breaths; such as arise from wine, &c. And these spirits are of two kinds; the one of crude, and the other of living bodies. The crude spirits are contained in all tangible bodies; but the living

See the axioms at the end of the History of Life and Death.

spirit only in such as are animated, whether of the vegetable or sensitive kingdom. 3. But there are no more than two pure pneumatical bodies, viz. air and flame: though these also are subject to great diversity, and receive very unequal degrees of extension.

A Table of pneumatical bodies; conformable to the preceding speculation; as they receive in order, a greater degree of extension.

The volatile parts of metals and fossils.
The after-volatile parts of the same.

Vapours.
Fumes.

After-fumes.

Exhalations.

After-exhalations.

Breathis.

After-breaths.

Crude spirits, confined in tangible bodies.
Air.

Living spirit, confined in tangible bodies.
Flame.

We are next to consider the respective extensions of these pneumatical bodies; as well with regard to themselves, as to tangible bodies. And here it might be well, if the nature of levity, by an ascending scale, would elucidate and correspond to the rarifaction of bodies; as the nature

of gravity, by a descending scale, does to their density. But several difficulties interpose: as first, that the differences of motions in objects invisible, are not immediately perceived by the senses. Secondly, that in air, and the like substances, there is not found so strong an appetite of moving upwards, as men imagine. And lastly, if the air did move upwards: yet it is generally continued along with other air, the motion would be difficultly perceived. For as water does not preponderate in water; so air does not rise up against, and displace air. And therefore other methods must be invented.

There are certain considerable proofs of the proportionate expansions of pneumatical bodies, with regard to each other; shewing also at the same time, that the series of rarifaction expressed in the table, has a solid foundation: but for the precise degrees of this expansion, and the comparative expansion of a pneumatical with a tangible body, the enquiry is more difficult.

All fumes, whether primary or secondary, do not, it is highly probable, come up to the rarity of the air; they being visible; but the air invisible nor do they themselves remain visible after being mixed along with the air.

It is manifest that after-fumes are more subtile, and rarified, than fore-fumes; as being no other than the calxe's and resolutions of that

subtile body flame itself. And so it appears from experience, that though the numerous lights continue for a long time burning in a room, or large assembly, the air is not thereby unfitted for respiration; notwithstanding so many afterfumes are received into it: but if the lights were to be extinguished, and their fore-fumes, or fuliginous steams, to be received instead of the former; the air would soon prove suffocating to the company.

We likewise judge that all crude spirits confined in tangible bodies, are denser than air for the spirits of vegetables, dead creatures, or the like, do, upon their exhalation, manifestly detain some gross, or tangible parts; as appears from odours; which being nothing but fumes going out sparingly, and a little at a time: (as we see in such fumes and vapours as are visible;) yet if they meet with any suitable, or soft, tangible body, they apply themselves to it, stick therein and communicate their odour: whence, it is plain, that they obstinately retain an affinity with gross bodies.

But we conceive living spirits to be somewhat rarer than air; because they are a little like flame*; and again because upon careful experi

* See the axioms at the end of the History of Life and Death.

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