steel show magnetic effects, and this is what we should expect, as the electron movement is common to all atoms. None of these substances is equal to iron and steel in magnetic power, but why this is so is not understood. This brings us to the production of an electric current by the dynamo. Here we have a coil of wire moving across a magnetic field, alternately passing into this field and out of it. A magnetic field is produced, as we have just seen, by the steady movement of electrons, and we may picture it as being a region of the ether disturbed or strained by the effect of the moving electrons. When the coil of wire passes into the magnetic field, the electrons of its atoms are influenced powerfully and set in motion in one direction, so producing a current in the coil. As the coil passes away from the field, its electrons receive a second impetus, which checks their movement and starts them travelling in the opposite direction, and another current is produced. The coil moves continuously and regularly, passing into and out of the magnetic field without interruption; and so we get a current which reverses its direction at regular intervals, that is, an alternating current. This current may be made continuous if desired, as explained in Chapter IX. Such, stated briefly and in outline, is the electron theory of electricity. It opens up possibilities of the most fascinating nature; it gives us a wonderfully clear conception of what might be called the inner mechanism of electricity; and it even introduces us to the very atoms of electricity. Beyond this, at present, it cannot take us, and the actual nature of electricity itself remains an enigma. INDEX Accumulators, 38, 90. Alarms, electric, 120. Alternating currents, 71, 75. Amber, discovery of, 2. Ampère, 33. Arc lamp, 93. Armature, 68. Atlantic cable, 145. Atom, 287. Aurora borealis, 25. Automatic telephone exchange, 165. Aviation and “wireless,” 280. Bachelet “flying” train, 271. Bastian heater, the, 110. Battery, voltaic, 33. Bell telephone, the, 156. Bells and alarms, electric, 116. Blasting, 256. Bunsen cell, 223. Cable-laying, 150. Cables, telegraph, 144. Cell, voltaic, 29. Clocks, electric, 124. Coherer, the, 183. Commutator, 70. Compass, magnetic, 52. Condenser, 63. Conductors, 6. Conduit system, 83. Convectors, 109. Cookers, electric, 110. Creed telegraph, 137. Crookes, Sir W., 230. Current, electric, 30. Daniell cell, 31, 223. Davy, Sir Humphry, 93. Detector, in wireless telegraphy, 188, 198. Diamond-making, 113. Duplex telegraphy, 139. Dussaud cold light, 106. Dynamo, 66. Edison, Thomas A., 103. Electric cookers, 110. Electric heating, 109. Electric motor, 66. Electric lighting, 70, 75, 93. Electricity, early discoveries, 1; nature of, 287. Electro-culture, 258. Electrolysis, 224. Electro-magnets, 58.