person was always well cloathed with flannels, which were warmed upon him before he left the bell, and would not suffer the cold water to penetrate. His cap contained air enough to serve him a minute or two, then by raising himself above the bell, and turning the cock, he could replenish it with fresh air. This pipe he coiled round his arm, which served him as a clue to find his way to the bell. See Plate Miscellanies, Figs. 18 and 19. DIVISIBILITY, that property by which the particles of matter in all bodies are capable of separation, or disunion from one another. As it is evident that body is extended, so it is no less evident that it is divisible, for since no two particles of matter can exist in the same place, it follows, that they are really distinct from each other, which is all that is meant by being divisible. In this sense the least conceivable particle must still be divisible, since it will consist of parts which will be really distinct. Thus far extension may be divided into an unlimited number of parts, but with respect to the limits of the divisibility we are still in the dark. We can, indeed, divide certain bodies into surprisingly fine and numerous particles, and the works of nature offer many fluids and solids of wonderful tenuity; but both our efforts, and those naturally small objects, advance a very short way towards infinity. Ignorant of the intimate nature of matter, we cannot assert whether it may be capable of infinite di- vision, or whether it ultimately consists of particles of a certain size, and of perfect hardness. We shall add a few instances of the wonderful tenuity of certain bodies, which have been produced either by art, or discovered by means of the microscope among the works of nature. Mr. Boyle mentions that two grains and a half of silk was spun into a thread 300 yards long: and a lady spun from a pound of wool, a thread equal to 95 English miles in length. The ductility of gold likewise furnishes a striking example of the great tenuity of matter, for a single grain of this metal has been actually divided into at least half a million of particles, each of which is perfectly apparent to the naked eye. The animal, vegetable and even mineral kingdom furnish nu-, merous examples of the subtilty of matter. What for instance must be the tenuity of the odoriferous particles of musk, when we find that a piece of it will scent a whole room, in a short time, and yet will hardly lose any sensible part of its weight. The human eye, unassisted by glasses, can frequently perceive insects so small as to be barely discernible. Now it is obvious that the limbs, the vessels, and other parts of such animals, must infinitely exceed in fineness every endeavour of human art. But the microscope has discovered wonders that are vastly superior, and such indeed as were utterly unknown to our forefathers, before the invention of that instrument. Insects have been discovered so small as not to exceed the 10,000 part an inch in length: so that 1,000,000,000,000 of them might be contained in the space of one cubic inch yet each little animal must consist of parts connected with each other: with vessels, with fluids, and with organs necessary for its motions, for its increase, and for its propagation. How inconceivably small must those organs be, and yet they are, unquestionably, composed of other parts . still smaller, and still farther removed from the perception of our senses. DIURNAL, in astronomy, something relating to the day in opposition to nocturnal, which regards the night. DIURNAL arch, the arch or number of degrees that the sun, moon, or stars describe between their rising and setting. DIURNAL motion of a planet, is so many degrees and minutes as any planet moves in twenty-four hours. Hence the motion of the earth about its axis, is called its diurnal motion. The diurnal phænomena of heavenly bodies, arise from the motion of the earth round its axis: for since the earth turns round its own axis from west to east, every spectator on its surface must necessarily be carried round in the same way; and consequently those parts of the heavens which lie toward the east, will by and by come into his sight, and - those which are visible to him, will depart out of it toward the west. Hence it is that the spectator not being sensible of his own motion (the reason of which is, because all things about him move along with him), imagines the whole heavens to turn round the contrary way, viz. from east to west, every twenty-four hours, which is nearly the time in which the earth performs one revolution about its axis. Dock, in maritime affairs, is a pit, great pond, or creek, by the side of an harbour, made convenient either for building or repairing of ships. It is of two sorts: 1. Dry-dock, where the water is kept out by great flood gates, till the ship is built or re*paired, when the gates are opened, and the water |