Spectrum of sunlight, 18 Sun, mock, 64 Sunset clouds, 68, 69, 72, 73 Sunset sky, 72, 73 Thermopile, heating effects of, 36 Thermopile, principle of, 35 Ultramarine, light reflected from, 95 Ultra-violet rays, 31 Vermilion, light reflected from, 93 Vibrations of rays per second, 55 Violet bands, brightness of, 21 Visible and invisible parts of spectrum, 30 Water, particles of, 62 Wave-length of lines in solar spectrum, 26 White light and contrast colours, 200-202 White light, extinction of by colour, 131 White light, formation of by mixture of yellow and blue, 125 White light, how made, 114, 115, 119-123 White light, impression of, 81 Yellow and blue make white, 125 Yellow, chrome, luminosity of, 191 Yellow spot, 117 Young-Helmholtz theory, 138 THE END. Richard Clay & Sons, Limited, London & Bungay. PUBLICATIONS OF THE =Society for Promoting Christian Knowledge.= THE ROMANCE OF SCIENCE. A series of books which shows that science has for the masses as great interest as, and more edification than, the romances of the day. _Small Post 8vo, Cloth boards._ =Coal, and what we get from it.= Expanded from the Notes of a Lecture delivered at the London Institution. By Professor Raphael Meldola, F.R.S., F.I.C. With several Illustrations. 2_s._ 6_d._ =Colour Measurement and Mixture.= By Captain W. de W. Abney, L.B., R.E., F.R.S. With Numerous Illustrations. 2_s._ 6_d._ =The Making of Flowers.= By the Rev. Professor George Henslow, M.A., F.L.S., F.G.S. With Several Illustrations. 2_s._ 6_d._ =The Birth and Growth of Worlds.= A Lecture by Professor A. H. Green, M.A., F.R.S. 1_s._ =Soap-Bubbles, and the Forces which Mould Them.= A course of Lectures by C. V. Boys, A.R.S.M., F.R.S. With numerous diagrams. 2_s._ 6_d._ =Spinning Tops.= By Professor J. Perry, M.E., D.Sc., F.R.S. With numerous diagrams. 2_s._ 6_d._ =Diseases of Plants.= By Professor Marshall Ward. With Numerous Illustrations. 2_s._ 6_d._ =The Story of a Tinder-Box.= A course of Lectures by Charles Meymott Tidy, M.B., M.S., F.C.S. With Numerous Illustrations. 2_s._ =Time and Tide.= A Romance of the Moon. By Sir Robert S. Ball, LL.D., Royal Astronomer of Ireland. With Illustrations. 2_s._ 6_d._ MANUALS OF HEALTH.