14. =The Nature of Matter Unknown.=--What now, let us inquire, do we know of the nature of matter? Can we say that we know any thing of it? We may observe its phenomena, and learn its properties; but with our most searching analyses of it we can no more determine what matter is than we can what spirit is. Newton supposed "that God in the beginning formed matter in solid, massy, hard, impenetrable particles." This he believed to be true of liquids, and even of gases, as well as solids. In the gas these hard particles are much farther apart than in the solid. The supposition is a very probable one; but if it be true it does not let us know what matter is, for it leaves us in the dark as to the nature of the particles. Newton farther supposed that these particles have always remained unaltered amidst all the changes that are taking place; these changes being occasioned by "the various separations and new associations and motions of these permanent particles." When, for example, any thing is burned up, as it is expressed, not one of these particles is either destroyed or altered, but they merely take on new arrangements. Though most of the substance has flown off in the form of gas, the ultimate particles composing the gas are the same now that they were when making a part of the solid substance; and they may soon again become a part of some new solids. Such changes in the forms of matter are every where going on; and when you become acquainted with Chemistry, in the Second Part, you will be familiar with them. 15. =Atomic Theory.=--These ultimate particles of matter are so minute that they have never been seen by man. The smallest particle that can be seen with the most powerful microscope is probably made up of very many of them united together. These ultimate particles we term atoms; and the theory in regard to the composition by them of different substances is called the atomic theory. The atoms of different substances are not supposed to be alike, but to differ in both size and weight. This theory will be more particularly noticed in the Second Part. 16. =Imponderable Agents.=--There are certain agents--light, heat, electricity, etc.--which are supposed by some to be forms of matter. If they are, they are exceedingly attenuated; for their presence, as has been proved by many experiments, never adds in the least to the weight of any substance. They have therefore been styled imponderable agents. Their agency is of great importance and very active, producing every where constant changes. Two of them--heat and light--are obviously and immediately essential to life. What their real nature is remains as yet an entire mystery. CHAPTER II. PROPERTIES OF MATTER.