Index of Spectra: Appendix S is a book written by William Marshall Watts and published in 1908. This book is a comprehensive index of spectra, which are the unique patterns of light emitted or absorbed by different types of matter. The book is organized alphabetically by element, and within each element, the spectra are arranged by wavelength. The book includes spectra for a wide range of elements, including hydrogen, helium, carbon, oxygen, and many...