VI.--THE ELECTRIC TELEGRAPH. Needle instruments--Influence of current on, 129. Mainspring, invention of, 59. Compound locomotives, 62. Compound microscope, 261. Condenser, marine, 71, _72_; of Ruhmkorff coil, 121, _122_. Safety-valve, 32, _33_, 391. Sand-glasses, 411. Scissors, action of, _450_. Secondary winding of dynamo, 161, _172_. Bunsen burner, 409. Burning-glass, 232. Camera, the, 233; pinhole, _234_, _235_. Canals, semicircular, 273. Capillary attraction, 392; veins, 358. Carbon dioxide, 27, 359; monoxide, 27. Carburetter, 98, _99_. Cardan shaft, 93. _Carmania_, the, 83. Centrifugal force, 382. Change-speed gear, 105, 442. Chassis of motor car, 110; railway, 187; vacuum, 189, _190_, _191.