FAST AND HEAVY RAIILLWAY SERVICE. 233 
train would average 135 to 160 amperes, according to the 
voltage. 
In starting, during certain periods of acceleration and 
on grades, much more current is required. From Fig. 119 
we may judge that the current, even at 600 volts working 
pressure, might well rise to 400-500 amperes, while to 
maintain schedule on a grade of, say, two or three per cent 
would demand fully as much. Altogether the maximum 
working current per train must be taken as high as 500 
amperes, although this amount would be seldom called for. 
The supply of so great a current to the moving train is 
not altogether a simple matter, and has involved consider- 
able experimentation. 
The ordinary street car trolley burns badly with such 
F1G. 120. 
currents, and special wheels arranged to secure extra large 
contact with the trolley wire are needful, while sometimes 
two independent trolleys have helped the matter. 
The trolley wire itself is necessarily of large cross sec- 
tion, so large as to involve some trouble in support, and 
several unusual shapes have been tried to improve the con- 
tact area and facilitate suspension. Fig. 120 shows two 
such forms, the simpler of which is in use on a portion 
of the Nantasket Beach electric road. Neither shape is 
unobjectionable, though both give a good opportunity for 
gripping the wire firmly in the clamps without forming 
projections which would be likely to throw off the trolley 
when running at high speed. Both are likely to give 
trouble from twisting, so as to make poor contact with the 
trolley wheel. 'The more nearly circular the cross section 
of the wire can be made, while still permitting projections