It is hoped that the work will be accepted as a text-book in Organ Schools and Conservatories of Music, leading toward, and lending help to, a branch Of study Of the greatest value and impor tance to the organ student; but one which, in too many quarters, has been seriously neglected. That a thorough knowledge of the tonal forces Of the Organ and their varied powers in scientific and artistic combination and registration, for the production Of special and expressive qualities Of both compound, unimitative organ, and imitative orchestral tones, is essential to the accomplished organist, admits of no question. Accordingly, it is highly desirable that the student should leave the organ school with, at least, a foundation laid for that thorough knowledge. It is with the earnest desire to contribute effectively to the laying Of that foundation that the present work is placed at the command of both teachers and pupils.