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Page:Popular Science Monthly Volume 56.djvu/585

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569
WHAT MAKES THE TROLLEY CAR GO.

tially filled with water. If water could be excluded from the conduit, the casing; c c, in the first figure, and the tube f, in the second one, would not be required, for there is no difficulty in providing an insulating support that will hold the conductor firmly in place and at the same time prevent the escape of the current; but as soon as moisture collects upon the surfaces of the insulating supports it acts as a conductor, and thus renders the insulation of little value.

PSM V56 D0585 Underground conduit with exposed conductors.png
Fig. 27.—Underground Conduit with Exposed Conductors.

If water runs into the conduit in such quantities as to come in contact with the conductor, then the effect of the insulation is entirely destroyed; the aim of the inventors, therefore, is to provide means for preventing the accumulation of water or moisture around the conducting wire. It can be readily seen that the shorter the conductor the easier it is to protect it, and this fact has given rise to the development of a great number of designs classified as sectional conductors. In these, two conductors are used, one of which