For the Consideration of my Dear Friend David Rittenhouse Esqr

Universal Space, as far as we know of it, seems to be fill’d with a subtil Fluid, whose Motion, or Vibration, is called Light.

This Fluid may possibly be the same with that which being attracted by and entring into other more solid Matter, dilates the Substance, by separating the constituent Particles, and so rendering some Solids fluid, and maintaining the Fluidity of others: of which Fluid when our Bodies are totally depriv’d, they are said to be frozen; when they have a proper Quantity, they are in Health and fit to perform all their Functions; it is then called natural Heat; when too much it is called Fever; and when forc’d into the Body in too great a Proportion from without, it gives Pain by separating and destroying the Flesh and is then called burning, and the Fluid so entring and acting is called Fire.

While organiz’d Bodies animal or vegetable are augmenting in Growth, or are supplying their continual Waste, is not this done by attracting and consolidating this Fluid called Fire, so as to form of it a Part of their Substance; and is it not a Separation of the Parts of such Substance which dissolving its solid State, sets that subtil Fluid at Liberty, when it again makes its appearance as Fire.

For the Power of Man relative to Matter, seems limited to the dividing it and mixing the various kinds of it, or changing its Form and Appearance by different Compositions of it, but does not extend to the making or creating of new Matter, or annihilating the old: Thus if Fire be an original Element or kind of Matter its Quantity is fix’d and permanent in the Universe. We cannot destroy any Part of it, or make addition to it. We can only separate it from that which confines it and so set it at Liberty, as when we put Wood in a Situation to be burnt; or transfer it from one Solid to another, as when we make Lime by burning Stone, a Part of the Fire dislodg’d from the Wood being less in the Stone.

May not this Fluid when at Liberty be capable of penetrating and entring into all Bodies organiz’d or not: quitting easily in totality those not organiz’d, and quitting easily in part those which are; the part assum’d and fix’d remaining till the Body is dissolved.

Is it not this Fluid which keeps asunder the Particles of Air, permitting them to approach or separating them more in Proportion as its Quantity is diminish’d or augmented?

Is it not the greater Gravity of the Particles of Air, which focus the Particles of this Fluid to mount with the Matter to which it is attach’d as Smoke or Vapour?

Does it not seem to have a great Affinity with Water, since it will quit a Solid to unite with that Fluid, and go off with it in Vapour, leaving the Solid cold to the Touch, and the degree measurable by the Thermometer?

The Vapour rises attached to this Fluid but at a certain height they separate, and the Vapour descends in Rain retaining but little of it, in Snow or Hail less. What becomes of that Fluid? Does it rise above our Atmosphere and mix with the universal Mass of the same kind?

Or does a Spherical Stratum of it, denser or less mix’d with Air, attracted by this Globe, and repell’d or push’d up only to a certain height from its Surface by the greater Weight of Air remain there, surrounding the Globe and proceeding with it round the Sun.

In such case, as there may be a Continuity or Communication of this Fluid thro’ the Air quite down to the Earth, is it not by the Vibrations given to it by the Sun that Light appears to us; and may it not be, that every one of the infinitely small Vibrations, striking common Matter with a certain Force enter its Substance, is held there Attraction, and augmented by succeeding Vibrations, till the Matter has receiv’d as much as their Force can drive into it?

Is it not thus that the Surface of this Globe is continually heated by such repeated Vibrations in the Day, and cooled by the Escape of the Heat when those Vibrations are discontinu’d in the Night, or interrupted and reflected by Clouds?

Is it not thus that Fire is amass’d in and makes the greatest Part of the Substance of combustible Bodies?

Perhaps when this Globe was first form’d and its original Particles took their Place at certain Distances from the Centre in proportion to their greater or less Gravity the Fluid Fire attracted towards that Center might in great Part be oblig’d as lightest to take place above the rest, and thus form the Sphere of Fire above suppos’d Which would afterwards be continually diminishing by the Substance it afforded to organiz’d Bodies; and the Quantity restor’d to it again by the Burning or other Separating of the Parts of those Bodies?

Is not the natural Heat of Animals thus produc’d, by separating in digestion the Parts of Food, and setting their Fire at Liberty?

Is it not this Sphere of Fire which kindles the wandring Globes that sometimes pass thro’ it in our Course round the Sun, have their Surface kindled by it, and burst when their included Air is greatly rarified by the Heat on their burning Surfaces?

May it not have been from such Considerations that the antient Philosophers suppos’d a Sphere of Fire to exist above the Air of our Atmosphere?