Vassenius describes the rose-coloured solar prominences in 1733, 204

Vitellio, his skill and conscientiousness, 14
——­his investigations respecting light, 207

Voltaic battery, use of, and its production of heat, 6, 7

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

Wuensch, 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