PREFACE TO THE TENTH EDITION OF
THIS Part, even in its original form, contained large portions which were re-
written rather than translated, and the last two chapters had no place at all
in the original French. In the sixth edition the numbering of the chapters
and sections was altered, to make it consecutive with the other three parts,
and additional matter was introduced under several heads. In the seventh
edition two pages on Concave Diffraction Gratings were added. The tenth
edition contains additions relating to beats, recent measures of the velocity of
light, goniometers, convex mirrors, and nodal points of lenses.
BELFAST, March, 1838.
NOTE PREFIXED TO FIRST EDITION.
IN the present Part, the chapters relating to Consonance and Dissonance,
Colour, the Undulatory Theory, and Polarization, are the work of the Editor;
besides numerous changes and additions in other places.
The numbering of the original sections has been preserved only to the end
of Chapter LX.; the two last chapters of the original having been transposed
for greater convenience of treatment. With this exception, the announcements
made in the "Translator's Preface," at the beginning of Part I., are applicable
to the entire work.