INFRA-RED rays, 32 Interference, 13 KIRCHOFF'S law, 40 LANGLEY, Bolometer, 32, 48, 49, 77 Lebedew, pressure of light, 65 Lummer and Pringsheim, law of radiation, 48, 50 MAGNETIC oscillations, 20 Maxwell, electromagnetic theory, 17 -- pressure of light, 64 Momentum of moving electric field, 81 NEWTON, dispersion, 29 -- corpuscular theory, 12 -- law of cooling, 46 Nichols, Rubens and, Rest-strahlen, 79 Nicholls and Hull, pressure of light, 64, 68 PFLÜGER, emission from tourmaline, 43 Phase, 22 Phosphorescence, 59 -- chemical theory of, 61 -- temperature and phosphorescence, 62 Planck, energy and wave-length, 51 Polarised light, emission from tourmaline, 42 Pressure of light, prediction of by Maxwell, 64 -- measurement by Lebedew, 65 -- measurement by Nicholls and Hull, 64, 68 -- on the earth, 68 -- on fine dust, 69 -- on comets' tails, 69 -- three effects of in astronomy, 70 Prévost, Theory of Exchanges, 46 RADIATING power, 38 Radiometer action, 67 Reflection, corpuscular theory, 11 -- of electric waves, 87 Refraction, corpuscular theory, 11 -- of electric waves, 87 Resonance, 30 Rest-strahlen or residual rays, 79 Ripples on mercury, 13 Ritchie, radiating and absorbing powers, 38 Rowland, gratings, 73 Rubens and Kurlbaum, proof of Planck's law, 51 Rubens and Nichols, Rest-strahlen, 79 SCHUMANN waves, 78 Simple harmonic motion, simple periodic motion, 24 Spark discharge, 84 Spectrometer, 76 -- reflecting, 78 Spectrum, 29 -- the whole, 32 -- incandescent solid or liquid, 33 -- incandescent gas, 33 -- analysis, 34 -- emission and absorption, 34 -- sun, 35 -- stars and nebulæ, 36 -- and temperature, 48 Stationary waves, 88 Stefan, law of radiation, 47 TEMPERATURE, absolute, 56 -- of planets, 54 -- of space, 55 -- of sun, 53 ULTRAVIOLET rays, 32, 77 WAVE form, 24 Wave-length, 22 -- range of, 80 -- of electric waves, 90 Wave theory, rectilinear propagation, 13 Wien, Law of Radiation, 50 YOUNG, interference, 16 Printed by BALLANTYNE, HANSON & CO. Edinburgh & London /tb THE PEOPLE'S BOOKS "A wonderful enterprise, admirably planned, and deserving the highest success."--_The Nation_. THE FIRST DOZEN VOLUMES 5. +BOTANY: THE MODERN STUDY OF PLANTS+. By M. C. STOPES, D.Sc., Ph.D., F.L.S. "A wonderful 'multum in parvo,' and cannot fail, by its lucidity and pleasant method of exposition, to give the reader not only a clear conception of the science of botany as a whole, but also a desire for fuller knowledge of plant life."--_Notes and Queries_. 10. +HEREDITY+. By J. A. S. WATSON, B.Sc. "Accurate, and written in a simple manner which will stimulate those who are interested to wider reading."--_Athenæum_. 12. +ORGANIC CHEMISTRY+. By Professor J. B. COHEN, B.Sc., F.R.S.