ELECTRIC TRUNK-LINE OPERATION——-SPRAGUE. 145 
them with heavy passenger traffic, and operated under greatly vary- 
ing conditions. A large proportion of these roads have used the or- 
dinary type of top-contact rail, carried by insulators on the ties, 
sometimes entirely exposed, and again partly guarded by side boards, 
as on the Manhattan Elevated, or by a wooden shield carried by 
yokes from the rail itself, as on the Interborough. While this is the 
simplest form of third-rail construction, and has given good service 
for years, it has certain disadvantages. If exposed, it is a constant 
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1 
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Fic. 2.—Details of Wilgus and Sprague protected third rail. 
menace, especially in yards; and even when guarded it can not be 
wholly protected from snow and ice. The lower part is only about 
4 inches above the tie, while the holding clips generally used reduce 
even this clearance, so that the danger of grounding from accumula- 
tion of wet snow and ashes, and from flooding is increased. In the 
latter case over-all flooding has the whole rail surface for leakage. 
These various objections led to the abandonment of the top-contact 
rail in connection with the New York Central work, and the develop- 
ment of an under-contact sheathed rail supported by insulators from 
