Fig. 25 shows one of the forms of a class of underground conduits belonging to the inclosed conductor type. The track rails are supported upon the outer ends of large castings, _F F_, commonly called yokes. These are made of such size that the portion below the opening which incloses the conduit may be of sufficient depth to afford the requisite strength to properly support the track. The conductor that carries the current is located at _f_ and is insulated from the casing _j_, which forms the lower half of the conduit, by the stands _g_. From the car a bar, _P_, which is called a plow, projects downward through the slot between the rails, _k k_, and on its end is spread out into a fork, _d_, which carries a pulley, _e_. When this pulley is in contact with the conductor _f_ the current passes through the plow _P_ to the motors upon the car, and thence to the track rails and back to the power house. As the yokes _F F_ and the conduit casing _j_ are made of iron and are in metallic connection with the track rails, it is evident that if the conduits should fill with water to the depth of the wire _f_ the current would pass directly to the rails, and thus would avoid the longer path through the motors. To prevent this occurrence, the sides of the conduit are inclosed with the sheet-iron covers _c c_, which nominally are in the position shown by the dotted lines _i i_. The plow is also provided with the arms _b b_, upon the ends of which are mounted small wheels _a a_, and these run upon tracks attached to the covers _c c_. As is shown in the figure, the wheels _a a_, running upon the tracks attached to the covers _c c_, cause the latter to spread out to the position in which they are shown. This spreading, as can be readily understood, only takes place for a short distance ahead and behind the plow, but at all other parts of the conduit the sides assume the position _i i_, and thus close the conduit and exclude the water. It can be easily seen that some difficulty would be encountered in making a tight joint at _h h_, and also that the opening and closing of the sides might not operate as perfectly in practice as upon paper, but it does not follow from these facts that the design is not practical; it simply illustrates that there are many minor difficulties to be overcome in order that complete success may be attained. Many designs operating upon this principle have been patented, and in some of them a great amount of ingenuity is displayed. [Illustration: FIG. 26.--UNDERGROUND CONDUIT WITH INCLOSED CONDUCTOR.]