DIVISIBILITY, the capability of being separated into parts. A metaphysical problem, long discussed by philosophers on abstract prin ciples, is the divisibility of matter. The micro scope reveals only to an infinitely small extent the subdivision of substances and tissues, or ganic and inorganic. Even in the mechanical productions of art distinctness of subdivision is amazing. A slip of ivory, of an inch in length, has frequently a hundred equal parts marked on it, all being distinctly visible. Nobert, a Pomeranian optical instrument maker, is re nowned for producing the finest rulings on glass which have hitherto been executed. These test plates, as they are called, contain a number of bands, the coarsest of which in his 20-band plate contains 11259 spaces to the inch, and the finest 225,187. Yarn has been spun so fine that one pound of it extended 4,770 miles.
The gold-beaters begin with a ribbon an inch broad and 150 inches long, which has been reduced by passing through rollers, to about the 800th part of an inch in thickness. This rib bon is cut into squares, which are disposed be tween leaves of vellum, and beaten by a heavy hammer till they acquire a breadth of more than three inches, and are therefore extended 10 times. These are again quartered, and placed between the folds of gold-beaters' skin and stretched out, by the operation of a lighter hammer, to the breadth of five inches. There seems almost no limit to the gold-beater's skill in dividing his tissue of gold, for one grain of gold has been beaten out to a surface of 52 square inches, and leaves have been made 367, 500 of which would go to the inch. Iron, the least malleable of the above-mentioned metals, has been reduced to wonderfully thin sheets. Fine tissue paper is about the 1,200th part of an inch in thickness, but at the exhibition of 1851 Gillott, the steel penmaker, exhibited rolled sheets of iron the 1,800th part of an inch in thickness. Since then a sheet has been pro
duced with an area of 55 inches, weighing but 20 grains and having a thickness of 1-4800th part of an inch.
It has been asserted that wires of pure gold can be drawn of only the 4,000th part of an inch in diameter. But Dr. Wollaston, by an ingenious invention, obtained wires of platinum much finer than this, some of them only the 30,000th part of an inch in diameter. Such excessive fineness is hardly surpassed by the filamentous productions of nature. Human hair varies in thickness from the 250th to the 600th part of an inch. The fibre of the coarsest wool is about the 500th part of an inch in diam eter, and that of the finest only the 1,500th part. The silk line, as spun by the worm, is about the 5,000th part of an inch thick; but a spider's line is perhaps six times finer, or only the 30,000th part of an inch in diameter; insomuch that a single pound of this attenuated substance might be sufficient to encompass our globe. A single grain of sulphate of copper will communicate a fine azure tint to five gallons of water. Odors are capable of a much wider diffusion. A single grain of musk has been known to perfume a large room for the space of 20 years. Some germs are almost inconceivably minute. Thus the germ known as micrococcus is a minute spherical body sometimes no greater in diameter than the 32,000th of an inch. The minute organ isms to which the name of bacteria is specially applied are rod-shaped bodies about 1,000th of an inch in length. Many of the so-called in fusorial animalcules are so exceedingly small that myriads of them may exist in a drop of water.