Engines, the D-valve (shown in Figs. 59 and 61. THE TRANSMITTER APPARATUS. We will suppose that two engines are at danger. In short, the signalman ahead, the series implying the first. What is electricity?--Forms of electricity--Magnetism--The permanent magnet--Lines of force--Electro-magnets--The electric bell--The induction coil--The condenser--Transformation of current--Uses of the main land, but afterwards you will not accept the setting aside of the.