there had been the use of fire, where there is not the use of reason! When the ancient philosophers contemplated this wonderful privilege of man, his enjoying the use and the dominion of the element of fre, that Πανεχνο τουρος σελας, the brightness of fire, the universal artificer! as Eschylus expresses it, the likeness of God himself! they persuaded themselves, as it was a privilege too great for him in the beginning, that it must have been originally stolen from heaven; and that this very theft was the crime which brought all manner of evil upon the world!

LET

LETTER XVI.

NEXT, if not equal in rank to fire, comes the element of air; an element of which avarice cannot deprive us, and which power cannot monopolize. * The treasures of the earth, the verdure of the fields, and even the refreshment of the stream, are too often seen almost entirely appropriated to the luxuries of the great; while the less fortunate part of mankind stand humble spectators of their encroachments. But the air, no limitation can bound, nor any landmarks restrain. In this benign element, all mankind have to boast of an equal possession; and for this we have all equal obligations to heaven. While we live, we consume a part of this element for our sustenance; and when we die, our perishing bodies render back the supply, which, during life, we had accumulated from the general mass.

Air, in philosophy, is a light, fluid, transparent substance, surrounding the earth to a very considerable height. The word in Greek is ang. The ancients understood the nature of

* Animated Nature,

this element. They looked upon it as a general menstruum containing the volatile parts of all the bodies and substances in nature; which being combined and differently agitated, produced that variety of fermentations, meteors, tempests, and other effects, which daily fall under our observation. They knew also its weight, although they have not transmitted us any experiments on that head. The air is generally esteemed a fluid, though it differs from the general nature of fluids, in these particulars: 1. In being compressible, a property unknown to any other fluid. 2. In being uncongealable, or incapable of being fixed by any known method, as all other fluids may 3. In being of a different density in every part, decreasing from the earth's surface upwards; whereas other fluids are of an uniform density throughout. The air is therefore a fluid sui generis, if it be properly any fluid at all. In the heathen mythology, it was worshipped by some sectaries, under the names of Jupiter and Juno; the former representing the superior and finer part of the atmosphere, and the latter the inferior and grosser part. Of the internal structure, however, of this element, it is more than probable we shall never attain the knowledge.

It

Recherches sur l'Origine des Découvertes attri

buées aux Modernes.

It is too subtile, too tenuous a substance to be perceptible to us with all the advantages of the finest glasses. But its properties are well ascertained; and the most essential are fluidity, gravity, and elasticity.

From the researches made into the nature of

this imperceptible, but most powerful agent, it has appeared, not only that it is a constituent ingredient in animal and vegetable life, but that it is essentially requisite in every stage of both one and the other. Nay more, besides animal and vegetable life, it has been found, that it is no less indispensably necessary to the existence of sound, of fire, and of explosion. For example, as in an exhausted receiver an animal cannot live, so neither can a bell be heard, an inflammable body be kept burning, nor gun-powder be exploded, though made to fall on iron which shall be red hot. And in proof, with regard to the first of these instances; if the air be extracted that is in the body of an animal, the animal is squeezed flat by the pressure of the external air, and expires in an instant. On the other hand, if the circumambient air be exhausted, the internal air dilates itself to such a degree, that the animal will swell till it bursts. The weight of the air is equal to thirty-two feet of water,

3

water, each cubic foot weighing about seventy pounds; so that a column of air, a foot in diameter, weighs about 22,000 pounds weight. Yet, as it acts with equal force on either side, neither animal nor plant is injured by it. Thus, place a flat surfaced bottle empty on its side, and the elasticity of the air within it will prevent the weight of the atmosphere from breaking it exhaust, however, the air, and the force of the external air on its surface will make it fly into a thousand pieces.

This elasticity of air arises from the particles not joining so intimately as the particles of other fluids. A particle of fire being repulsive, forms a center to every certain number of particles of air, and so keeps them in a state of separation. And hence too the reason why air can be so greatly compressed. In regard to weight, the power of gravity in air is very considerable, though not equal to its elasticity, or to its repulsive force. Were the power of gravity to be for a moment suspended from matter, and the power of elasticity to remain, the atmosphere would instantly be dissipated through the regions of space. * The particles of air at the highest elevation,

VOL. I.

N

Martin's Philosophy.