Water, deportment of, considered and explained, 105, 106 Waves of water, 51 ----length of a wave, 52 ----interference of waves, 53-55 Wertheim, M., his instrument for the determination of strains and pressures by the colours of polarized light, 134 Wheatstone, Sir Charles, his analysis of the light of the electric spark, 202 Whirlpool Rapids, illustration of the principle of the interference of waves at the, 55 Willigen, Van der, his drawings of spectra, 202 Wollaston, Dr., first observes lines in solar spectrum, 193 ----discovers the rings of Iceland spar, 209 Woodbury, Mr., on the impurity of natural colours, 37 Wünsch, Christian Ernst, on the three simple colours in white lights, 39 _note_ ----his experiments, 39 _note_ Young, Dr. Thomas, his discovery of Egyptian hieroglyphics, 49; ----and the undulatory theory of light, 49 ----Helmholtz's estimate of him, 50 ----ridiculed by Brougham in the 'Edinburgh Review,' 50 ----generalizes Grimaldi's observation on light, 56, 57 ----photographs the ultra-violet rings of Newton, 160 End of the Project Gutenberg EBook of Six Lectures on Light, by John Tyndall