Mozart is the great virtuoso who, even as a boy, was the astonishment of Europe. It is not to be expected that he should content himself with the intimate reflectiveness of the pianoforte; he drags it out into the great world; he needs the concerto-form just as he needs great concert halls. The new pianoforte, with its fuller and more subtly expressive tones, is precisely adapted to his aims, and he is the first to launch the pianoforte on its decisive career. With his triumphal progresses the popularity of the new instrument was not likely to decline. The great enchanter leaves the tiny victories of the spinet far behind; his public recitals in hired halls, which henceforward become more and more popular, demand new feats. He has to work on bold lines; he has to bring into use the special features of the instrument he adopted; the rippling scale-passage, the variety of tone, the _forte_, the _pianissimo_, the hundred gradations between these extremes, the altogether new possibilities of sentimental expression which were now at the disposal of the public performer. But amid all the intoxication of the concert hall, the virtuoso remains an artist; the idol of the hour retains his deeper feeling. As he was only truly himself when, after the furore of publicity, he touched the notes in solitude or before a few friends, so in his concertos, behind the external glitter, a romantic soul lies hidden. In the beautiful Romance in the D minor Concerto, for example, the soul looks out on us with a wonderful and never-to-be-forgotten intensity. In almost all his pieces Mozart composes according to the bidding of the moment. He is an “occasional” composer. In the concertos the occasion was his own appearance on the stage. In the duets and double pianoforte pieces he found the occasion in his association with his sister. From this species of performance he drew new effects. The D major sonata for two pianos stands alone in the skilful and effective blending of the two instruments. His four-handed sonatas are astonishingly successful in the individualisation of the hands, and started a numerous class of clavier-pieces which have been too often misused. We shall not appreciate such duets, if we take the clavier as a diminutive orchestra.[109] But here again Mozart has been unwilling utterly to sacrifice combined effects to individual demands. [Illustration: Beginning of Mozart’s A minor Sonata. Royal Musikbibliothek, Berlin.]