CHAPTER XI

.--EPOCH OF YOUNG AND FRESNEL.

_Sect._ 1. Introduction. 92 _Sect._ 2. Explanation of the Periodical Colors of Thin Plates and Shadows by the Undulatory Theory. 93 _Sect._ 3. Explanation of Double Refraction by the Undulatory Theory. 98 _Sect._ 4. Explanation of Polarization by the Undulatory Theory. 100 _Sect._ 5. Explanation of Dipolarization by the Undulatory Theory. 105 {9}

## CHAPTER XII .--SEQUEL TO THE EPOCH OF YOUNG AND

FRESNEL.--RECEPTION OF THE UNDULATORY THEORY. 111

##