This ever active and unabatable something within us which compels us always to be marking time we may call, for want of a better name, the instinct of rhythm. It is the æsthetic principle of our nature. Translated into words it has given us poetry; into sound, music; into motion, dancing. Perhaps even painting may be referred to it, space being the correlative of time, and color the correlative of tone. We are fond of arranging our minute intervals of time into groups. We find certain of these groups highly agreeable, while others are no end unpleasant. In the former there is a singular regularity to be observed, which led hard-headed old Leibnitz to the theory that our delight in music arises from an inherent affection for mathematics. Yet musicians have hitherto obtained but indifferent recognition for feats of calculation, nor have the singing and playing of renowned mathematicians been unanimously commended by good judges. Music so intensifies and excites the instinct of rhythm that a strong volition is required to repress its physical expression. The universality of this is well illustrated by the legend, found in some shape in many countries and languages, of the boy with the fiddle who compels king, cook, peasant, clown, and all that kind of people, to follow him through the land; and in the myth of the Pied Piper of Hamelin we discern abundant reason to think the instinct of rhythm an attribute of rats. Soldiers march so much livelier with music than without that it has been found a tolerably good substitute for the hope of plunder. When the foot-falls are audible, as on the deck of a steamer, walking has an added pleasure, and even the pirate, with gentle consideration for the universal instinct, suffers his vanquished foeman to walk the plank. Dancing is simply marking time with the body, as an accompaniment to music, though the same--without the music--is done with only the head and forefinger in a New England meeting-house at psalm time. (The peculiar dance named in honor of St. Vitus is executed with or without music, at the option of the musician.) But the body is a clumsy piece of machinery, requiring some attention and observation to keep it accurately in time to the fiddling. The smallest diversion of the thought, the briefest relaxing of the mind, is fatal to the performance. 'Tis as easy to fix attention on a sonnet of Shakspeare while working at whist as gloat upon your partner while waltzing. It can not be intelligently, appreciatively, and adequately accomplished--_crede expertum_.