Kirchhoff,43Laplace,317nebular hypothesis,317Larmor, Dr.,22,44,56,63,93,163on electrons,284on aetherial physics,22,327-9Lavoisier,42Law of gravitation,24of inverse squares,27Laws of electricity,184of light,145of heat,113of motion,9,15,233Lead,88,333Lebedew,32,76,153Le Verrier,25discovery of Neptune,25Leyden jar,157Liebnitz,223Light,75a mode of motion,122corpuscular theory of,123undulatory theory of,123,136electro-magnetic theory of,156path of a ray of,144intensity of,145reflection of,136refraction of,135aberration of,149composition of,139velocity of,148zodiacal,277transverse vibration of,130Lines of force, electric,173magnetic,201-3Liquefaction of gases,47Liquid air,47Liquids,48Little Bear,307Dog,307Lockyer,109Lodge, Dr.,219on aether density,69on aether,284,289,328,332on electric inertia,330on electricity,64,69,284,285on force,17on gravitation,283Lorentz on light,154Lyra,307MacLaurin,2,10,17Magnesium,79Magnet,21Magnets, bar,199moving,211Magnetic axis,202field,199lines of force,200shells,205equator,202induction,199variation,208molecules of,193polarity,194Magnetism of earth,207-12of planets,211cause of solar,211Ampère's theory of,193Mars,68,79a magnet,196rotation of,219size of,236orbital velocity of,251satellites of,178orbit of,33Mass,27,53,187of earth,235,242of planets,235,242of sun,190Matter, elements of,40properties of,42,50and motion,41,322conservation of,42divisibility of,44four states of,48aetherial basis of,48,333physical constitution of,334Maxwell, J. C.,43,73,85,151,211on physical lines of force,168,203-5,288on aether,59,206on magnetism,205on electro-kinetic energy,180,217on aether,58Mayer,84,86,114,118McCullagh,75Mechanical energy,87Medium, Descartes on a,221Kepler on a,222Mercury,68,79a magnet,196rotation of,219eccentricity of orbit,33mass of,242orbital velocity of,251Meteorites,95,118Meteors,31,85,118Michelson and Morley,7,67Milky way,79,309,314Molecules,44Momentum,20Moon,61Motion of stars,310planetary,253of sun,274of aether,80and work,95modes of,92,122,163first law of,15,16,239second law of,19,244third law of,20,251Multiple stars,308Natural philosophy,4Nebulae and aether,313structure of,314spiral,322annular,320elliptical,320planetary,321spectrum of,314irregular,319Nebular hypothesis,317Nebulous stars,311Neptune,68discovery of,25mass of,235orbital velocity of,251,265distance from sun,242a magnet,196Newton's coloured rings,107Optics,72,98,122letter to Bentley,2,96Rules of Philosophy,3Principia,3,7,38emission theory,123law of gravitation,24atoms,44on aether,98Nichols and Hull,32,153Ocean,81,90Operations, cycle of,114Optics, Newton's,2,122Orbital motions of planets,266Orbit of earth,33of Venus,33Orbits of satellites,34of planets,33-4,266moon,267stars,310sun,270Origin of sun's heat,95Orion,79,307,314,319Oxygen,40,44,60,93Parallelogram of forces,15Pendulum,88Periodic times,37Perpetual motion,93,220Phil. Mag.,58,67,71,73,74,80Phil. Trans.,58,62,64,75Philosophy, Rules of,3Phobos,38Physical lines of force,203-6Pitch of Sound,105,120,139Plane of ecliptic,277-9Planetoids,31Planets, minor,31origin of,240orbits of,33,266electrified bodies,177masses of,242relative distances of,242orbital velocities of,251periodic times of,251Platinum,48Pleiades,79Polarization,176Potential energy,87Potential, electric,170magnetic,194Pouillet, M.,109Poynting,91Pressure, aetherial,181Preston, Prof.,283Prevost, theory of exchanges,105Primitive impulse,9,10,12,319Principia, Newton's,3,7,38-9,122Properties of matter,42Quantity of sun's heat,109Query,18-19Optics,72,122Radiant heat,109energy,115Radiation,104Radius Vector,26Rankine,103Rays, actinic,141dark heat,140infra-red,141ultra-violet,140Rontgen,341X,341Rectilinear propagation of light,144of heat,111Reflection,160Refraction,160Relative motion of aether and matter,224-6Resistance to motion,17Resisting medium,228Reversible cycle,116,118Rings, vortex,45Rival theories,8Rivers,89-90Roemer, and velocity of light,148Rotation of earth,219of planets,219of sun,246Rotatory motion,93Rucker, Prof.,59Rules of Philosophy,3first,3second,4third,3,7Rumford,98Running water,95Satellites of Mars,38,178Jupiter,149,178Uranus,254Neptune,254Saturn,26-7,68mass of,235,242orbital velocity of,251,265rotation of,219density of,242a magnet,196satellites of,178Schuster, Prof.,8,218,311Sirius,306,308-9Sodium,43Solar system, motion of,257,271spectrum,79,139magnetism,211Sound,75waves,104,120Space, interstellar,310,313Spectroscope,47,79Spectrum analysis,50,139Spiral nebulae,322Stars, fixed,58number of,11,306binary,309distances of,280magnitude of,306,309colour of,79,308motion of,310-11nebulous,320proper motions of,312variable,307double,308clusters of,314orbits of,310are magnets,307Stokes, Sir G.,69,152,218String,21Sun, diameter of,280constitution of,79a magnet,164,198-9mass of,190heat of,109motions of,270orbital velocity of,35rotation of,246centre of two forces,186Tails of comets,300,304straight,300curved,301multiple,300Tait, Prof.,18,40-1,88,247Telescope,79Temperature,104-5Terrestrial magnetism,207-12gravity,29Theory, atomic,44rules for making,3undulatory,123of exchanges,105Thermodynamics, first law of,87,114second law of,116Thomson, J. J., Prof.,43,326,335Tidal water-power,88Tides,89,96Torsion balance,185Trade winds,96,249Transformation of energy,86of motion,93Transverse vibration of light,130Tuning-fork,104Tympanum,120Tyndall on radiation,104,106on light,71on Lines of Force,174on aether,77on atoms,106on aether waves,112Ultra-violet rays,140red rays,140Unity of universe,322-9Universal gravitation,24aether,58Universe,313,322,347Uranus,68mass of,235density of,242orbital velocity of,265a magnet,196Ursa Major,307Minor,307Vapour,49Variation, magnetic,209-11Velocity of light,148of electric waves,182of heat waves,148of falling bodies,21of wave motion,76Velocity, angular,250Venus,33,68,79a magnet,197mass of,235rotation of,219