This is the succession of chords which children strum when they try to play accompaniments on the piano. It is the simplest progression of harmony we have, and lies at the basis of all our common tunes. It is called diatonic harmony because it is formed of chords on the whole tones of the scale, in contradistinction to chromatic harmony, founded on the chords of the semitones. It is necessary to speak of chromatic harmony here, because Cyprian di Rore made a special study of it, and his "Chromatic Madrigals," published in 1544, had a great influence upon the progress of music. The old church scales were essentially diatonic, and chromatic harmonies were not practicable in music written in those scales. Di Rore's madrigals were influential in showing composers how they could write more flexibly and more beautifully by breaking the shackles of the old Gregorian scales. Still, most of the music of that time continued to be essentially diatonic, for the composers had just begun to explore the possibilities of chord modulation. These possibilities do not seem to have been exhausted even by the music of Wagner. The development of secular music at this time was remarkable. The scientific composers began to make a practice of writing music to be used outside of the church. They wrote madrigals and other part-songs of real merit, and in them they made attempts at expression. Of course these first attempts were purely imitative. The composers tried to imitate natural sounds and movements in music. Gombert wrote a clever and humorous "Bird Cantata." Jannequin, in his "Cris de Paris," tried to paint the street life of the French capital, while his "Le Bataille" is a military picture in music. These remarkable descriptive pieces were written for four voices, unaccompanied, and in polyphonic style. After trying to tell some kind of a story in secular music they tried it in religious music. One of Willaert's motets, at any rate, tells the story of Susannah, and is plainly a forerunner of the oratorio. We have seen now how the first period of the Netherlands school brought contrapuntal technics to a high state of development, how the second period produced a genius and a desire for pure beauty, and how the third period introduced a broader, simpler, and more imposing style into church music and made definite attempts at expression. We now come to the fourth period, which was destined to bring ecclesiastical counterpoint to its perfection. This period also produced a master of splendid genius, whose works live yet and ought to live as long as there is a place in the Roman Church for pure and lofty music. This man was Roland Delattre, usually known by the Italian form of his name, Orlando Lasso, or di Lasso.