It has also been discovered more recently that in the operation of
electric railways in which the track rails form part of the circuit, a
considerable increase in the tractive adhesion of the driving wheels
is manifested, due to the passage of the return current from the
wheels into the track. In the Baltimore and Hampden electric railway,
using the Daft "third rail" system, this increased tractive adhesion
enables the motors to ascend without slipping a long grade of 350 feet
to the mile, drawing two heavily loaded cars, which result, it is
claimed, is not attainable by steam or other self-propelling motors of
similar weight. In the two instances just cited the conditions are
widely different, as regards the nature of the current employed, the
mechanical properties of the surfaces in contact, and the electrical
resistance and the working conditions of the respective circuits. In
both, however, as clearly demonstrated by the experiments hereinafter
referred to, the cause of the increased friction is substantially the
same.
In order to ascertain the practical value of the electric current as a
means of increasing mechanical friction, and, if possible, render it
commercially and practically useful wherever such additional friction
might be desirable, as for example in the transmission of power, etc.
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