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.
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 con-