DIRECT FEEDING SYSTEMS. 67 
cient to interfere with the proper operation of the cars. If 
we write for the maximum permissible drop, V, o for the 
drop corresponding to the loss of energy for greatest econ- 
omy of transmission, for the load factor, I, and for the drop 
assumed, V1, we have the following inequality which sets 
a limit of drop which must not be exceeded 
i £l 
Very fortunately it usually happens that 
v Ll 
so that there is no special difficulty in making 't = 7. 
But it is not safe to assume this happy condition of things 
Hundred K. W, 
       
111 
§9 B0 S0 TR 68 T 8 TN 0R10 P RETY AL URE g IR DG e ST S 
Time M Time 
Street Ry. Journal 
  
  
  
10 11 12 
F1G. 4s5. 
without some investigation. = It may be true of one part of 
the system and not of another. It is necessary therefore to 
look into the various parts separately in laying out any con- 
siderable system. Fig. 45 shows three load curves which 
may be supposed to be from three parts of the same system, 
together with the summation curve of the three from which 
the total load factor would be determined. I may be taken 
as the Joad curve of a main urban system, while curves IT 
and IIT will serve for branches. IV is the summation 
curve of the whole. 'The load factor of this final curve is 
very evidently worse than that of the main line, curve I, 
since heavy loads in morning and evening on branches II 
and IIT raise the morning and evening maximum values