A canon is a species of imitation, the most strict and exact of all imitations, written according to rule (καυώυ), the idea being that one voice shall start a melody and some other voice follow with the same melody a few beats later on, imitating the first voice note for note, and usually interval for interval, either at the unison, the octave, or some other distance. At one period canons were made musical puzzles, by the composer writing only the first part (called the “dux,” or leader), and then, by some sign over one of the bars, indicating at what point the following voice (or “comes”) should come in, the latter singer having to guess the correct interval at which he was expected to enter. However ingenious such riddles may be, they do not help art. A catch at first greatly resembled the round, where a complete continuous melody was written out, and when one singer had reached a certain point in this melody, another singer had to begin, and _catch up_ his part in time—the difference between catch and canon being that in the former each part imitates at the same pitch; in the latter the imitation may be at any interval from the original voice. Besides, many canons are connected with sacred words, and introduced into our cathedral services, whereas the catch, in the reign of that dissolute monarch, Charles II., degenerated into an improper play upon words, assisted by music. At a later date, in the eighteenth and at the beginning of this century, this idea of the singers “catching at each other’s words,” so as to alter the meaning of those words, was cleverly used by S. Webbe, Dr. Callcott, and others. A well-known example by the latter will best explain the effect produced:— “_Ah! how, Sophia_, could you leave Your lover, and of hope bereave?” “_Go, fetch the Indian’s_ borrowed plume, Though richer far than that you bloom.” “_I’m but a lodger_ in her heart, Where more than me, I fear, have part.” The result of one voice entering after another is, that the first seems to be shouting, “A house a-fire!” the second excitedly answers, “Go, fetch the engines!” whilst the third excuses himself by saying, “I’m but a lodger!” After all, these could only be considered ingenious trifles, and most of the singing clubs have turned their attention to the more interesting and higher forms of madrigal, glee, and part song, which, as a later development, we will now speak of. PART SONG. A part song is most likely to prove itself a melody harmonised, in three, four, or more parts—that is to say, there will be but little contrapuntal or imitative writing about it. It is of German origin; but it has been imported into our country, and our native composers have written some very beautiful specimens.