and therefore of a definite size and weight, though so minute as to defy all our optical instruments to enable us to perceive them; others hold them to be mere points or centres of force, destitute of solidity and magnitude. What is an atom? This is a problem which the human mind can never solve, it can only throw out shrewd guesses at the truth. We will, however, take it for granted that the ultimate particles of matter are indivisible and indestructible, without wasting our time on metaphysical subtleties.
Though we can form no conception of the absolute size of atoms, the wonderful divisibility of matter furnishes many proofs of their extreme minuteness. The gold-beater hammers out a single grain of the precious metal until it covers forty-nine square inches. Now, each square inch of this gold leaf may readily be cut into a hundred strips, and each strip into a hundred pieces, each of which is distinctly visible to the unaided eye. A single grain of gold may thus be subdivided into 490,000 visible parts. But this is not all; if attached to a slip of glass the leaf may be subdivided still further, as ten thousand lines may then be ruled in the space of a square inch, and in this manner the entire leaf, weighing but a grain, may be cut into 4,900,000,000 fragments, each visible by means of the microscope. As we require no less than ten figures to express the number of parts into which a grain of matter may be subdivided by mechanical means, and as each of these parts must contain a vast
