Before entering into a description of the means by which this result is produced, and how it is proposed to apply this method practically to railway and other purposes, it may be well to give a general outline of what has so far been determined. These experiments have shown that the coefficient of friction between two conducting surfaces is very much increased by the passage therethrough of an electric current of _low electromotive force and large volume_, and this is especially noticeable between two rolling surfaces in peripheral contact with each other, or between a rolling and a stationary surface, as in the case of a driving wheel running upon a railway rail. This effect increases with the number of amperes of current flowing through the circuit, of which the two surfaces form part, and is not materially affected by the electromotive force, so long as the latter is sufficient to overcome the electrical resistance of the circuit. 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. It will be apparent at once that a method of increasing the tractive power of the present steam locomotives by more than 50 per cent. without adding to their weight and without injury to the roadbed and wheel tires, such as is caused by the sand now commonly used, would prove of considerable value, and the same holds true with respect to electrically propelled street cars, especially as it has been found exceedingly difficult to secure sufficient tractive adhesion on street railways during the winter season, as well as at other times, on roads having grades of more than ordinary steepness. As this, therefore, is probably the most important use for this application of the electric current, it has been selected for illustrating this paper.