Burney errs in supposing that these songs were written in so many parts. Three and four parts were the rule; five parts were extremely rare. The actual words of Il Lasca, who wrote the introduction to the collection of Triumphs and Carnival Songs published in Florence, 1559, are: "Thus they traversed the city, singing to the accompaniment of music arranged for four, eight, twelve or even fifteen voices, supported by various instruments." This would not necessarily mean what musicians call "fifteen real parts." The subject has been exhaustively and learnedly studied by Ambros,[24] who has examined the frottola in all its varieties. He has given several examples and among them he calls attention to a particularly beautiful number (without text) for five voices. This, he is certain, is one of the carnival songs which Heinrich Isaak was wont to write at the pleasure of Lorenzo. [Footnote 24: "Geschichte der Musik" von August Wilhelm Ambros. Leipsic, 1880.] The source of our knowledge of the frottola music is nine volumes of these songs, averaging sixty-four to the volume, published by Petrucci at Venice between 1504 and 1509, and a book of twenty-two published at Rome by Junta in 1526. Ambros's study of these works convinced him that the composers "while not having actually sat in the school of the Netherlanders, had occasionally listened at the door." The composers of the frottole showed sound knowledge of the ancient rules of ligature and the correct use of accidentals; on the other hand it is always held by the writers of the early periods that an elaborately made frottola is no longer a frottola, but a madrigal. Thus Cerone[25] in the twelfth book of his "Melopeo" gives an account of the manner of composing frottole. He demands for this species of song a simple and easily comprehended harmony, such as appears only in common melodies. So we see that a frottola is practically a folk song artistically treated. [Footnote 25: "El Melopeo y Maestro," by Dominic Pierre Cerone. Naples, 1613. (Quoted here from Ambros.)] "He who puts into a frottola fugues, imitations, etc., is like one who sets a worthless stone in gold. A frottola thus ennobled would become a madrigal, while a madrigal, all too scantily treated, would sink to a frottola." A typical frottola by Scotus shows observance of Cerone's requirements. [Musical Notation]