The spectroscope consists of a glass prism, or series of prisms, mounted between two metal tubes. One tube is provided at one end with a vertical slit, through which the light that is to be examined is passed. At the other end of the tube is a lens, so that the beam of light from the slit emerges through the lens as a pencil of parallel rays. The pencil of light then falls upon the glass prism, striking it at an angle. In passing through the prism, the light is bent round so that it enters the second tube, which is simply a small telescope. The prism separates the æther waves according to their wave-lengths, and produces the well-known coloured spectrum, which is magnified by the telescope. The reason for the bending of the different waves is explained in the electron's story. INDEX Absorption of light, 148 Æther, the, 24 Æther waves, 96, 131, 133, 137, 146, 148, 163 Alpha rays from radium, 190 Alternating electric current, 121 Amber electrified, 32, 34 to 37, 201 Artificial light, 140, 142 Atoms breaking up, 188, 190 Atoms co-operating with electrons, 108, 123 Atom's internal energy, 187, 191 Atoms of matter, 52, 54, 78, 128, 180, 184 Attraction between atoms, 180 Attraction, electrical, 35, 202 Attraction, magnetic, 78, 205 Aurora, 132 Automatic telegraph transmitter, 91 Battery, electric, 70, 203 Beginning of the world, 53 Beta rays from radium, 189 Birth of the moon, 52, 54 Bricks of the universe, 180, 195 Chemical affinity, 206 Chemical combinations, 56, 182 Chemistry of the stars, 52, 55, 144, 153 Chlorine atoms, 56, 182 Cloud formation, 56 Circuit, earth, 72 Coherer, tube, 98 Cohesive force, 183 Colour, 136 Compass needle, 77 Complete electric circuit, 71 Conductors, 37, 68 Connecting link between æther and matter, 118, 127 Corpuscles, 66 Crookes, Sir William, 205 Current of electricity, 68 Dark lines in spectrum, 154 Detachable electrons, 78, 181 Detecting imitation diamonds, 174 Direct electric current, 121 Discharge of electricity, 42 Discharge through a vacuum, 60 Discovery of electrons, 160, 206 Discovery of X-rays, 169 Dynamo, 116, 118 Earth circuit, 72 Electrical discharge, 42 Electricity, positive, 23, 32, 39, 52, 180 Electricity, negative, 23, 32, 39 Electric battery, 70 Electric current, 68, 70 Electric motor, 116, 122 Electric shock, 47 Electrified objects, 37, 38, 201 Electro-magnets, 76, 81, 83, 118, 205 Electrodes, 61 Electrocution, 49 Electron as a go-between, 118 Electron, derivation of the word, 23 Electron, discovery of, 160, 206 Electrons, 25, 32, 66, 78, 138, 162, 195 Energy transmission through the æther, 73, 121 Energy within the atom, 187, 191 Field, magnetic, 68, 76, 118 Fluorescent screen, 169, 206 Galvani's discovery, 202 Gamma rays from radium, 189 Gilbert's discovery, 201 Glass, electrified, 37, 38 Glass prism, 147, 152 Glow-lamp, electric, 140, 141 Glow-worm, 142 Heat, radiant, 126, 131, 133, 142 Helium atoms, 188, 190