Opera, then, generally speaking, is an Art form, in which a stage play is presented with all usual accessories, but with the important addition of continuous music: this is a general definition, but one of which there are so many modifications that we must turn aside for a moment to trace how it happens that so many forms and varieties of opera as there seem to be have sprung into existence. CHAPTER II. DIFFERENT SCHOOLS CORRESPONDING WITH THE GROWTH OF MUSICAL ART. The centuries see little change in the elements of the drama—Growth of opera concurrent with the progress of the art of music—Points of difference between early operas (Monteverde, etc.) and those of Scarlatti and later writers—Birth of the aria—England and France of the same date—Opera buffa—Musical empiricism—Gluck—His followers—Varying subjects treated—Italian opera —Abuses by the singers—Wagner and modern opera. [Sidenote: =Little change in the Drama=] The changes that have taken place in opera during the short three hundred years which constitute the life of modern music are far more prominent and important than those that have been undergone by the ordinary dramatic work: the arts of elocution, gesture, and stage action are very old ones, and have seen little radical change for many centuries. Great progress has been made through the use of modern mechanical devices and inventions in the mounting of all stage pieces—_i.e._, in the scenery employed, the lighting, and stage effects generally: these all appeal to the eye; but the appeal to the ear is not, in an ordinary dramatic work, more powerfully made than it was in the days of the Greek dramatist. But when music is added, then appeal to the ear of a most powerful kind takes place, and during the whole life of the youngest of the Arts the improvements and growth in musical technique and expression have been grafted upon opera with continuously progressive power and effect. [Sidenote: =Growth concurrent with the progress of the Art of Music=] Now, since opera has demanded for its representation an art that has been in a state of continuous growth, it will follow that the different classes of opera will closely correspond with the different styles and schools of music: we shall find therefore that the earliest operas were only able to employ crude and undeveloped music, none better being available; that as musical skill and knowledge grew, as additional instruments were added to the orchestra, as knowledge of forms developed, so all these improvements found their way into operatic music, with the result that the difference between say a seventeenth and an eighteenth century opera is a very wide one, while a vaster difference still may be seen between one of the eighteenth and one of the late nineteenth century. We may briefly examine the causes of these differences, taking the dawn of all modern music (about 1600 A.D.) as the starting-point.