FUNDAMENTAI, PRINCIPLES. 2.
as each is from its neighbor. This example, however,
shows a common characteristic of long lines.
The network type of distribution found in railway prac-
tice is quite different in character and needs from a light-
ing network. Itis, save in a few instances, such as Fig.
4 (see page 4), much less complex and isalways much more
irregular in load. In a well ordered central station for
electric lighting, every street in the business district has
its main, and the load, while far from regular, does not
exhibit the extreme variations found in electric railway
work.
The general solution of even a simple network, to find
the current (and thence the drop) in each line due to one
or more known load points, involves a most forbidding
amount of tedious computation. But for the purpose in
hand exact solutions are not needed so much as easy ap-
proximations.
Consider, for example,the simple network of conductors
shown in Fig. 14. A is here the source of supply, either
the station or the end of a feeder. 'The load is distributed
along the lines, AD, AE, D:E, DF, EF, D C, F B and
C B. Such a circuit may be said to consist of three meshes,
and it contains eight currents which we may call Z,, Z, etc.
In lighting practice it is necessary, knowing the load to be
supplied by each line, to figure the conductors so as to
maintain uniform voltage throughout the network. This
involves algebraic processes too complex for convenient use;
in fact the complete solution is a very pretty problem in
determinants, which those interested may find elucidated in
Maxwell’s ‘‘ Treatise on Electricity and Magnetism,’”’ and
somewhat simplified in a paper by Herzog and Stark, pub-
lished in 18go. For railway work the conditions are,
fortunately, simpler. We know, or can assume with suffi-
cient accuracy, the normal distributed load on each of the
lines. But we are absolved from any necessity for keeping
closely uniform voltage throughout the system, since, even
were it a matter of more importance than it ever 1is, it
could only be accomplished by using an enormous excess of
