This increase in frictional adhesion is principally
noticeable in iron, steel, and other metallic bodies, and is due to a
molecular change in the conducting substances at their point of
contact (which is also the point of greatest resistance in the
circuit), caused by the heat developed at that point. This heat is
ordinarily imperceptible, and becomes apparent only when the current
strength is largely augmented. It is therefore probable that a portion
of this increased tractive adhesion is due directly to the current
itself aside from its heating effect, although I have not as yet been
able to ascertain this definitely. The most economical and efficient
results have been obtained by the employment of a transformed current
of extremely low electromotive force (between 1/2 and 1 volt), but of
very large volume or quantity, this latter being variable at will, so
as to obtain different degrees of frictional resistance in the
substances under observation.
These experiments were originally directed mainly toward an endeavor
to increase the tractive adhesion of the driving wheels of locomotives
and other vehicles, and to utilize the electric current for this
purpose in such a manner as to render it entirely safe, practical, and
economical.
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