*Series.* One following directly after the other; in electrical connections, the wires attached in line from positive to negative, through the different cells. *Series multiple.* A wiring system wherein the cells are placed in two or more groups, and the groups connected up in series. *Segment.* A portion of a disk cut off by a straight line. Distinguished from a sector which is made by two radial lines running from the center to the circumference. *Self starting.* A mechanism on automobiles for starting the engine without muscular effort. *Self-inductance.* In electricity, the property of one metal to receive an electrical charge without being in contact with the charged wire. *Selective.* The term applied to a system of transmission, whereby the driver is able to select any speed without going through any intermediate speed. *Service brake.* The brake ordinarily used in running a car. *Semi-floating.* An axle in which the wheels are secured directly to the axle shafts, but where the reaction of the differential and bevel gear drive is supported by the axle housing. *Shackle.* A device for restraining or holding. *Simultaneous.* At the same time; occurring at the same moment. *Solution.* To solve a question. To dissolve solid matter in a liquid. *Soapstone.* A rock which has a structure similar to that of soap. *Speculate.* To consider a subject from the standpoint of probabilities. *Sprocket.* A wheel with teeth in it adapted to engage with a chain, for driving purposes. *Spur gear.* A gear with teeth which are at right angles with the body of the gear. *Spline.* A rib usually along the side of a shaft, to engage in a groove in the hub or wheel.