This little book is written in the hope that it may be 
of service to those whose daily work is concerned with 
the art of transportation, in which electrical traction is 
to-day so potent a factor. 'The part it may play to-morrow 
only the prophet can say. 
The author has endeavored to set forth the general 
principles of the distribution of electrical energy to mov- 
ing motors, to describe the methods which experience has 
shown to be desirable in such work, and to point out the 
ways in which these principles and methods can be co-or- 
dinated in everyday practice. The art of correctly design- 
ing systems of distribution requires, more than anything 
else, skilled judgment and infinite fizesse; it cannot be 
reduced to formulee in which these terms do not enter as 
variables. The most that can be done is to sketch the 
lines of thought that, followed cautiously and shrewdly, 
lead to good results. 
For the most part apparatus is too mutable to describe 
exhaustively, unless one is writing history. The reader 
will therefore find little of such detail, save in the frontier 
region which lies between established tramway practice 
and that greater field that stretches toward unknown 
bounds. Along that frontier experiment has blazed paths 
here and there, and we must note them carefully. We 
can see whither they lead, but dare not say how far. 
The best advice that can be given to the engineer is 
to keep his eyes and ears open and never to let himself get 
caught out of sight of experimental facts. 
L B, Nov, 1,/ 1806,