Fig. 26 illustrates another type of inclosed conductor which at a first glance appears to be far superior to that just described, but upon closer investigation it is found to be not wholly free from objections that are difficult to overcome. The yoke _F F_, as in the design just described, is made wide enough to support upon its outer ends the track rails _R R_, and is cut away in the middle to an outline conforming with the shape of the conduit. The conductor that carries the current is located at _d_, being supported by the stands _e_. An elastic tube _f_ is provided, which is water-tight and thus excludes moisture from its interior, within which the conductor _d_ is located. On the top of tube _f_ a flexible rail _b_ is secured, and this connects with studs _c_, which are within the tube, as clearly shown in the drawing, and so situated that they may be forced down into contact with _d_. Normally these studs are separated from _d_, but when the car comes along, the wheel _a_, mounted upon the end of plow _P_, flattens the tube _f_ and thus forces one or more of the studs _c_ into contact with _d_. The distance between the studs _c_ is such that at least two will always be in contact with _d_, thus insuring a continuous electrical connection with the motors so long as the plow is depressed. The first impression upon looking at this design would be that it is entirely free from objections; for if we assume that the tube _f_ is made of rubber, we can see it in our mind's eye springing up after the plow passes by and thus separating the contacts _c_ from _d_, and at the same time yielding freely to the pressure of the wheel _a_. All of this is true, but rubber is not very durable when under such exposed conditions, and to maintain a length of several miles of it in a perfect state for even two or three years could not reasonably be expected; and if it became necessary to renew the tube oftener than this the cost of maintenance would be entirely too great. There is another objection, however, which is more serious, and that is that the conduit will gradually fill up with dirt, and this pressing against the rubber tube would force it out of shape, and thus cause the contacts _c_ to bear permanently upon _d_, or else to become so far displaced that they would not touch it when depressed by the plow.