RECENT PROGRESS IN ELECTRICITY. 
171 
skirts of the city and distributing direct current through a 
much shorter length of mains, thus allowing larger amounts 
of current to be carried with a permissible drop. So far, this 
system seems to be a success, both in increasing the number 
of lamps which can be connected and also in reducing the 
cost of production of power, and hence it will probably come 
into general use. 
The same method has been used for furnishing current to - 
city street railways, necessitated here also b}^ the immense 
amount of power which has to be furnished and which, at 
the low voltages, would necessitate an amount of copper in 
the conductors which would be prohibitive. The result has 
been the erection of immense stations, capable of supplying 
power for a whole city, in units of no less than 5,000 horse¬ 
power. The ability to place such stations on tide-water 
where coal and condensing water can be cheaply obtained, 
in conjunction with every device possible for rendering their 
operation independent of manual labor, will result in con¬ 
siderable economies in operation. 
b. Long Distance Transmission .—Few improvements have 
been made in this direction. The number of lines has been 
increased, and some extremely large plants are being pushed 
to completion. The largest of these are at Niagara, Lachine, 
and Chambley. The Assuan plant, on the Nile, will be in 
operation within a few years, and will do much to develop 
Egypt, which will probably become a large cotton manu¬ 
facturing center. Large projects are now under way in 
India and elsewhere. The two remaining great opportuni¬ 
ties of the future are at the falls of Zambesi and those on 
the northern tributary of the Ganges. 
Recent work has tended to set a limit to the distance at 
which long-distance transmission is possible. Considering 
economic considerations alone, the distance at which trans¬ 
mission is profitable, except under exceptional conditions, 
may be put as roughly one mile for each thousand volts of 
potential used. But the experiments of the Westinghouse 
Company have shown that at potentials of about 50,000 
