Corelli wrote his sonatas most frequently in four movements. The composers who immediately succeeded him wrote more often in three movements, but preserved the alternation of rhythm and tempo. Corelli used only one subject in each movement, and the development of it was of a simple nature compared to the developments found in subsequent works. Later composers found that in order to secure the necessary amount of contrast and variety, together with those points of repose which are essential to artistic form in music, it was necessary to have two principal themes of contrasting nature. The development of these themes was confined to the first movement, while the other movements were less complex in design. The Germans were not wholly idle in advancing the sonata, but it is extremely difficult to ascertain how their work and that of the Italians affected one another. We know that a violin sonata by H. J. F. Biber, published in 1681, shows a well ordered sequence of contrasting movements. The first was a very slow one (largo), in contrapuntal style; the second, a passacaglia (theme and variations); the third, rhapsodical and declamatory; and the fourth, a gavotte. Dr. Parry has pointed out that Biber received his suggestions for the first movement from church polyphony, for the second and fourth from dances, and for the third from operatic declamation. This sonata, however, shows nothing of that methodic repetition of subjects and definite distribution of keys now regarded as indispensable; and in some respects Corelli's sonatas were of a distinctly higher type. Following the admirable analysis of Dr. Parry, I may state here that as early composers gradually perceived the possibilities of the sonata form, they evolved this scheme for their alternation of movement:-- 1. Summons to attention, followed by appeal to intelligence through display of design. 2. Slow movement--appeal to the emotions. 3. Finale--lively reaction after emotion.