The limits of a paper such as the present are too confined, and perhaps the subject itself is too impalpable, to afford any hope that all the causes in the case mentioned in the title can be here set out in one view; the paper is therefore designated as only illustrating some causes. The term “tone-colour” has come to this country translated from the German, it is a word involving a metaphor, and it is just possible that twenty-five years ago it might have been resented by some as an affectation; but it is an accepted term of the enlarged musical diction of the present day. It conveniently expresses that total effect made on the ear by musical sounds, especially the collective sounds of the orchestra, which is dependent not on art structure proper but on the qualities and employment of the instruments which give interpretation to the art-idea. In a concert-room of to-day, an orchestra constituted so as to perform a Handel score, and one constituted so as to perform a Wagner score, differ entirely in tone-colour. Even where the constitution of the orchestra is the same, as say in performing works by Mendelssohn and Schumann respectively, the tone colour is different, because those two composers used the instruments differently. By the most modern orchestra in my title I mean that of a period not exceeding say the last fifty years, or the lifetime of many in this room, and in some particulars the remarks will have reference to the orchestra actually of the present day; many most able writers have treated of the historic growth of the orchestra, and the present paper is not to be regarded as historical in its aim except in the sense of drawing attention to some facts connected with the most recent developments.