By the tension in the wire the carrier arches acquire the necessary stability, while without the procedure previously described it would be impossible to use such light arches attached to the sleepers. On permanent lines, the extreme ends of the wire are attached to properly anchored picket posts. On portable lines, on the other hand, the trolley with the wire drum is fixed to the rails at the end of the line, as shown in Fig. 3, so as to enable the line to be lengthened or shortened, as may be required, with ease. [Illustration: FIG. 3.--THE STRAINING GEAR AND TERMINAL ANCHOR.] Care is taken in insulating the drum and ladders so as to prevent leakage from this erecting trolley to earth. The feeders from the power house to the overhead wire and to the rails respectively are erected on light iron posts, which have also been standardized by Mr. Koppel. A specimen of these posts with an anchored stay is shown in Fig. 4. All these details are arranged for convenience of the contractor required to rapidly equip a line of railway, which can also be removed as soon as the work has been done. [Illustration: FIG. 4.--LIGHT POLE FOR CARRYING THE FEEDERS.] [Illustration: FIG. 5.--THE KOPPEL LOCOMOTIVE.] The locomotive used is varied in form with the gage of the line, but we are particularly concerned with those for gages under 24 inches. One form of such locomotive without a hood to protect the driver is shown in Fig. 5. In this locomotive the gear is the same as that of the next illustration, but it is securely boxed in a watertight iron cover. The controlling gear is then placed vertically in front. Figs. 6 and 7 show the details of the electrical and mechanical parts of this locomotive when fitted with a platform at either end, and with a hood. The motor. M, is of the internal pole type, and is supported on the underframe of the wagon. A double gear is used. The first is a spur gearing, connecting the motor to a countershaft placed under the motor. This gear reduces the speed of rotation to about 200 revolutions. The countershaft is then connected to the two axles of the trolley by chain gearing. This gives the necessary flexibility between the car body and the wheel required, as the springs give to any inequality of the rails. In this gearing there is no change of speed. The underframe is provided with spring axle boxes, and also with spring buffers and drawbars. The speed of the motor can be regulated within very wide limits by the regulator, R. An effective hand brake is also provided. [Illustration: FIG. 6.--END ELEVATION OF LOCOMOTIVE.] [Illustration: FIG. 7.--DETAILED ELEVATION OF A KOPPEL LOCOMOTIVE WITH A DOUBLE PLATFORM AND HOOD.]