All this implies a growth of tonal perception on the part of the hearers, and especially of the ability to co-ordinate tonal impressions over a wide and constantly increasing range. For the hearer has in mind not only the particular tone which at the moment occupies his ear, and the others which preceded it, and a sort of inner feeling of the tone which will follow the present one, but also all the other tones over which the singer would pass in going from one tone to another. And unless he has this he cannot realize the true place of the melody tone in key, and therefore rests unconscious of its real expression. It is, indeed, possible for him to make a mistake in regard to the tones which he unconsciously associates with the tones actually heard--as, for example, when one hears an E followed by a C higher, and one thinks of the four white keys of the piano between them, while the melody may be thinking of the black keys between them. In the one case the melody would be in the key of C, in the other of C sharp minor. And the expression of the melodic skip would be enormously changed thereby. This larger education of the faculties of tonal perception and tonal co-ordination has been the work mainly of the last century and a half, and more particularly of the present century itself. During this period the progress has been more rapid than within any other in the entire course of the history of our art, and it is to the successive steps preparing for this that we now address ourselves. [Illustration] CHAPTER VI. THE MINSTRELS OF THE NORTH. Upon many accounts the development of minstrelsy by the Celtic singers and harpers was one of the most important of all the forces operative in the transformation of the art from the monody of the ancients to the expressive melody and rich harmony of modern music. As it is to a considerable extent one side of the direct course of this history, which hitherto has dealt largely with the south of Europe, the present is the most convenient time for giving it the consideration its importance deserves. I do this more readily because English influence upon the development of music has generally been underrated by continental writers, the erudite Fetis alone excepted; while their own national writers, even, have not shown themselves generally conscious of the splendid record which was made by their fathers.