As already mentioned in chapter XI, there was no measure notation for a long time after Franco's death. The data are uncertain concerning the exact time when the bar began to be used to mark the measure. Its earliest use was that of marking the end of the music belonging to a line of poetry. This is the same use as now made of the double bar in vocal music. In fact, everything points to the progressive development of music in all respects, and the development of what we might call self-consciousness in musicians, whereby each succeeding generation sought to place upon record a greater number of particulars concerning their music, and to leave less and less to accident or tradition. This progress has gone on until the present time, when two particulars of our music are exactly recorded--the pitch and the rhythm. The exact relation of every tone to the key note is ascertainable from our musical notation, and the precise degree of rhythmic importance appertaining to each tone according to its place in measure and in the larger rhythms. We are still lame in the matter of expression, and in pianoforte music also in regard to the application of the pedals. Here our notation affords only a few detached suggestions. If the master works of the modern school could be noted for expression as completely as for pitch and rhythm, the labor of acquiring musical knowledge would be very greatly diminished. The four-line staff has remained in use in the Catholic Church until the present time, and with it the square notes. It is generally called Gregorian, and by many is supposed to have been invented by Gregory the Great; but as a matter of fact, about six centuries elapsed after his death before this square-note notation came into use. The five-line staff came into use about 1500. Information is wanting as to the causes which led to its adoption in preference to the four-line notation so long in use. The clef for do (C clef) remained in use until very lately, and is still used by many strict theorists, being written upon the first line for the soprano, the fourth line for the tenor, the third line for the alto. The G clef, also, when first introduced, was often written upon the third or the first line; the F clef, moreover, was not definitely established on the fourth line until toward 1700. In the scores of Palestrina's work, now published in complete form, there are pieces written with the soprano in the G clef upon the first line, the alto in the C clef upon the second line, the tenor in the C clef upon the fourth line, and the bass in the F clef upon the third line. This, while affording the eye two familiar clefs, the treble and the bass, places them in such a way as to practically make it necessary for the modern reader to transpose every note of the composition in all the parts, and, in fact, to effect a transposition for each part upon principles peculiar to itself.