NEW YORK AND BOMBAY

1906




PREFACE TO THE FOURTH EDITION.


In these Lectures I have sought to render clear a difficult but
profoundly interesting subject. My aim has been not only to describe
and illustrate in a familiar manner the principal laws and phenomena
of light, but to point out the origin, and show the application, of
the theoretic conceptions which underlie and unite the whole, and
without which no real interpretation is possible.

The Lectures, as stated on the title-page, were delivered in the
United States in 1872-3. I still retain a vivid and grateful
remembrance of the cordiality with which they were received.

My scope and object are briefly indicated in the 'Summary and
Conclusion,' which, as recommended in a former edition, might be, not
unfitly, read as an introduction to the volume.

J.T.

ALP LUSGEN: _October_ 1885.