WHAT MAKES THE TROLLEY CAR GO. 



;6g 



tially filled with water. If water could be excluded from the con- 

 duit, 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. 



k 



FlQ. 27. — UXDERGE'IUND CoXDUIT WITH EXPOSED CONDUCTORS. 



If water runs into the conduit in such quantities as to come in con- 

 tact 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 con- 

 ductor the easier it is to protect it, and this fact has given rise to 

 the development of a great number of designs classified as sec- 

 tional conductors. In these, two conductors are used, one of which 



VOL. LVI. — 46 



