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, as less mixed with air, attracted by this globe, and repelled or pushed 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 of communication of this fluid through 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, enters its substance, is held there by attraction, and augmented by succeeding vibrations till the matter has received 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 discontinued in the night, or intercepted and reflected by clouds?
Is it not thus that fire is amassed, and makes the greatest part of the substance of combustible bodies?
Perhaps, when this globe was first formed, 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 centre, might in great part be obliged, as lightest, to take place above the rest, and thus form the sphere of fire above supposed, which would afterward be continually diminishing by the substance it afforded to organized bodies, and the quantity restored to it again by the burning or other separating of the parts of those bodies?
Is not the natural heat of animals thus produced, by separating in digestion the parts of food, and setting their fire at liberty?
Is it not this sphere of fire which kindles the wandering globes that sometimes pass through it in our course round the sun, have their surface kindled by it, and burst when their included air is greatly rarefied by the heat on their burning surfaces?
May it not have been from such considerations that the ancient philosophers supposed a sphere of fire to exist above the air of our atmosphere?
B. Franklin.