Aberration of light,69,149,218Absorption,104-6Acceleration,239Actinic rays,141Action at a distance,96,174,176and re-action,20,251Adams' discovery of Neptune,25Aether is matter,54-8is atomic,59-67is gravitative,64-9density of,69,71,136,243elasticity of,74-7inertia of,76,330its motions,80compressibility of,291,315waves,79-80Aetherial basis of matter,326Affinity, chemical,43Aldebaran,312Aluminium,79Ampère,192Ampère's theory of magnetism,193Andromeda,314Annual magnetic variation,208Annular nebulae,320Aphelion of earth,36Arago, M.,321Arcturus,312Areas, Kepler's law of,36Asten, Von,234,296Asteroids,31Atmosphere,68,73,102,225Atom, vortex,45,46,61what it is,43electron,63Boscovitch,61hard,61size of,43Attraction, electrical,2,286of gravitation,13,24,31magnetic,195Balance, Torsion,187Bernoulli,221,341Beta Persei,308Biela's comet,296-7Binary compound,143stars,25,309Biot,138Boscovitch atoms,44,138Boyle and Marriotte's law,76,103Bradley's discovery of aberration,149Bredichin on comets' tails,302Brilliancy of stars,307,309British Association Report,57,59Calcium,79Canis major,307minor,307Capella,312Carbon,48Carboniferous period,115Carnot on heat,116-18Cassini,307Cause and effect,14of gravitation,1,282-9Cavendish experiment,24Centauri,79Centre of gravity,325Centrifugal force,9,13,15,30,236-8Centripetal force,9,12,282Cetus,307Chalk,6Challis, Prof.,74,96,100,107,151,155,214,227,311Chemistry,47,336Coal,86,88Clairaut,297Clusters of stars,314Cohesion,48Colour,138Colours of stars,308seven primary,139Comets,291attracted by planets,298condensation of,292Comets and meteors,297short period,293-4long period,293-4tails of,298-9orbits of,293nucleus of,298-9coma,298-9Compressibility of aether,291,315Condensation of gases,47Conservation of matter,42of energy,84of motion,92Constellations,307Corollary,15Corona Borealis,309Corpuscles,42,64,136Corpuscular theory of light,122Correlation of forces,83Coulomb Torsion balance,185,187Crookes, Sir William,42,136,326,341Current, electric,163magnetic,192Currents,90Curry, Prof.,284Cycle of operations,114,116Cygnus,307Dalton's atomic theory,42Davy, 99,107Day and night,4D'Arrest's comet,296Deimos,38Democritus,44Density of matter,51of aether,69electric,170of earth,242of sun,27of planets,242Descartes,221-2,341Dewar, Prof.,47Diameter of earth,29polar,29equatorial,29of sun,280of planets,29Dielectric,168,175Diffusion,49Dip, magnetic,199Distances of stars,280Diurnal variations, magnetic,209Dog star (Sirius),306Donati's comet,298Double stars,308Draco,307Dynamical equivalent of heat,114value of light,150Dynamics, laws of thermo-,114-18Dynamo,87,90Ear,120Earth, mass of,235,242a magnet,196-8size of,29rotation of,219orbit of,276periodic time of,251gravity of,29shape of,29distance from sun,242,251velocity in orbit,251Eccentricity of orbits,268,276Eclipse,145,148Ecliptic, plane of,277-9Elasticity,46of matter,51of aether,74Electric current,154potential,170induction,175radiation,182density,170energy,179field,166,179lines of force,173Electricity,64,162two kinds of,175positive,175negative,175laws of,184theories of,162Electrons,136,163Electro-static,158,164kinetic,158,164kinetic energy,217magnetism,192-5magnets,199magnetic theory of light,229chemical equivalents,189,333Elements of matter,47Ellipse,34Kepler's discovery of,34Elliptical nebulae,320Emission theory of light,122Encke's comet,293,296resisting medium,228Energy,83,84what it is,83conservation of,84transformation of,86potential,87kinetic,89,164radiant,109electrical,179and motion,91Engine, Carnot's heat,116Envelopes of comets,298Epicureans,44Equal areas,36times,36Equator, N. and S. Poles,29magnetic,202terrestrial,29Equipotential surfaces,171Equivalents, electro-chemical,189,333Euler,123Exchanges, theory of,105Experience,4Experiments of Rumford,98of Michelson and Morley,67,227of Lebedew,302of Nichols and Hull,153of Hertz,165of Faraday,65,285of M. Faye,302of Joule,114Falling stone,21,29Faraday,45,175,220on matter,56on Lines of Force,168,200,203-5on magnetic space,208on gravitation,287on electricity,332on induction,176Faye, M.,111,302,319Faye's comet,293,296Field, electric,179magnetic,199Fizeau,149,224Fluids,48Food,89Forbes,121Force,16,19,90centrifugal,9,13,236centripetal,9,12,282lines of,200Forces, direction of the,26proportion of the,26Foucault,149Franklin,106Fresnel,75,131Frictionless medium,17,131,136,224Fundamental medium,54Galaxy,325,346Gaseous nebulae,313Gases, condensation of,47liquefaction of,47kinetic theory of,49Glazebrook, Prof., on aether and gravitation,22Globular clusters of stars,314Gravitation, law of,61,65universal,24intensity of,27law of proportion,26cause of,1,282and binary stars,25Gravity, centre of,325Great Bear,307Grove,83Halley's comet,296-7Hamilton, Sir W. R.,247Head of comets,298Heat is motion,98a mode of motion,107radiant,109dynamical equivalent of,116effects of,107nature of,98radiation of,109transformation of,87Heat engine, Carnot's,116of sun,109and matter,100and work,114refraction of,121Helmholtz, Von,45,86Hercules,257,271,307Herschel, Sir J.,3,4,7,226,228,281,299,301,310,321Sir W.,109,271-2,313Hertz,138,159,182Hicks, Prof.,13Hodograph of planets,247Hot springs,90Huggins,313-14Huyghens,54,123,125,128Hydrogen,40,42,44,60,93,314,333Hypotheses,3,338Ice,42Identity of heat and light,119light and electricity,156,160,165aether and electricity,331Imponderable,71Impressed force,20Impressible aether,78Induction, electric,174-5magnetic,199Faraday's theory of,175Inertia of matter,52of aether,330Intensity of light,28,146of heat,28,113of electricity,184of gravity,28Iron,42expansion by heat,101contraction by cold,102Joule, 85,114Jupiter, 26,68mass of,235satellites of,149,178rotation of,219orbital velocity of,251,265size of,235distance from sun,242,251density of,242and comets,305Kant,317Kelvin, Lord,43,71,77,80,95,216,227on aether,56-7on vortex atom,63on compressible aether,291,315on light,151Kepler's laws,32first,33,256-9second,36,260-2third,37,263-5on vortex motion,221-2Kinetic energy,89electro,217