I have said that the symphony evolved slowly under the laws of its own being, and I wish to state briefly and (as far as possible) in simple terms how that evolution came about. If I should go back to the very beginning I should have to point out that the primal difference between music and noise consists in the intensity of vibration and in the grouping of the sounds into regular series by means of accents. A series of unaccented tones does not make music. If a clock, in striking twelve, should, by accenting certain strokes, throw the whole number into regular groups, it would supply the basis for music. In any great piece of martial music these accents and these impulses in groups constitute the element that moves us to comply with it ourselves; we beat time with hand or foot; we are infused with the momentum. And the force of the impetus may be observed at the close of nearly every piece of music where conventional chords ease off its stress. The last forty measures of the Fifth Symphony of Beethoven constitute a sort of brake on the huge moving mass. Chopin’s Polonaise, opus 26, number 1, on the contrary, does not end; it stops. In Fielding’s “Tom Jones” the impetus of the action is carried on so far that the climax is postponed to a point dangerously near the end of the book, which leaves us with a sense of breathlessness or even of aggravation. In music, when this impetus is of extreme vigor, any temporary displacement of it produces almost the effect of a cataclysm--as in the first movement of Beethoven’s Third Symphony, where great chords in twos clash across already established metrical groups of threes. Within the metrical groups all sorts of subdivisions may exist, and these constitute what is called “rhythm” in music. Rhythm, in brief, is the variety which any melody imposes on the regular beats that constitute its time basis. It is from this rhythmic movement that the symphony gets its quality of action, and the precursors of the symphony in this respect were the old folk-songs and dance-tunes the melodies of which are full of rhythmic diversity. The line from these early naïve compositions down to symphonic music was never broken, and there is hardly a symphony in existence that does not pay direct tribute to them.