familiar objects belonging to the visible world. A many-spoked wheel, divested of its felly, will give the reader some idea of a common diatom;[1] but he must imagine the spokes to be formed of innumerable pieces joined together with the utmost nicety, and to be inserted in the nave with far greater regularity than that attainable by any human wheelwright. Yet this delicate wheel is formed of the hardest flint, and is so minute that its spokes are less than the three-hundredth part of an inch in length!
Another diatom has the appearance of a piece of lace edging, with crossing threads and oval openings arranged in a beautiful and perfectly regular pattern.[2] Another resembles a chain of flat beads, or rather, an open bracelet formed of oblong tablets. This simile, however, is far from being perfect; for the living tablets of the diatom are neither strung upon threads, nor connected by hinges, but are joined in some inexplicable manner at their corners.[3]
The boat-shaped diatoms, or Naviculæ, are perhaps the most beautiful of this minute family. One of them, an unnamed variety, has been thus described by an anonymous writer:—"The tiny bark is a boat of cut rock-crystal, fit to float across a sea of light; itself might almost be believed to be fashioned out of solidified light. The central line must be the keel; the translucent planking is clearly visible; and around the sides are cut symmetrical notches, to
