I have here a model car and track arranged to show the equipment and operation of the system as applied to railway motors. The current in the present instance is one of alternating polarity which is converted by this transformer into one having the required volume. The electromotive force of this secondary current is somewhat higher than is necessary. In practice it would be about half a volt. You will notice upon a closer inspection that one of the forward driving wheels is insulated from its axle, and the transformed current, after passing to a regulating switch under the control of the engineer or driver, goes to this insulated wheel, from which it enters the track rail, then through the rear pair of driving wheels and axles to the opposite rail, and then flows up through the forward uninsulated wheel, from the axle of which it returns by way of a contact brush to the opposite terminal of the secondary coil of the transformer. Thus the current is made to flow seriatim through all four of the driving wheels, completing its circuit through that portion of the rails lying between the two axles, and generating a sufficient amount of heat at each point of contact to produce the molecular change before referred to. By means of the regulating switch the engineer can control the amount of current flowing at any time, and can even increase its strength to such an extent, in wet or slippery weather, as to evaporate any moisture that may adhere to the surface of the rails at the point of contact with the wheels while the locomotive or motor car is under full speed.
It will be apparent that inasmuch as the "traction circuit" moves along with the locomotive, and is complete through its driving wheel base, the track rails in front and rear of the same are at all times entirely free from current, and no danger whatever can occur by coming in contact with the rails between successive motors. Moreover, the potential used in the present arrangement, while sufficient to overcome the extremely low resistance of the moving circuit, is too small to cause an appreciable loss of current from that portion of the rails in circuit, even under the most unfavorable conditions of the weather. In practice the primary current necessary is preferably generated by a small high speed alternating dynamo on the locomotive, the current being converted by means of an inductional transformer. To avoid the necessity for electrically bridging the rail joints, a modified arrangement may be employed, in which the electrical connection is made directly with a fixed collar on the forward and rear driving axles, the current dividing itself in parallel between the two rails in such a manner that, if a defective joint exists in the rail at one side, the circuit is still complete through the rail on the other; and as the rails usually break joints on opposite sides, this arrangement is found very effective. The insulation of the driving wheels is very easily effected in either case.
As the amount of additional tractive adhesion produced depends upon the quantity of current flowing rather than upon its pressure, the reason for transforming the current as described will be apparent, and its advantages over a direct current of higher tension and less quantity, both from an economical and practical standpoint, will for this reason be clear. The amount of heat produced at the point of contact between the wheels and rails is never large enough to injure or otherwise affect them, although it may be quite possible to increase the current sufficiently to produce a very considerable heating effect. The amount of current sent through the traction circuit will of course vary with the requirements, and as the extent to which the resistance to slipping may be increased is very great, this method is likely to prove of considerable value. While in some cases the use of such a method of increasing the tractive power of locomotives would be confined to ascending gradients and the movement of exceptionally heavy loads, in others it would prove useful as a constant factor in the work of transportation. In cases like that of the New York elevated railway system, where the traffic during certain hours is much beyond the capacity of the trains, and the structure unable to support the weight of heavier engines, a system like that just described would prove of very great benefit, as it would easily enable the present engines to draw two or three additional cars with far less slipping and lost motion than is the case with mechanical friction alone, at a cost for tractive current that is insignificant compared to the advantages gained. Other cases may be cited in which this method of increasing friction will probably be found useful, aside from its application to railway purposes, but these will naturally suggest themselves and need not be further dwelt upon.
In the course of the experiments above described, another and somewhat different method of increasing the traction of railway motors has been devised, which is more particularly adapted to electric motors for street railways, and is intended to be used in connection with a system of electric street railways now being developed by the author. In this system electro-magnetism provides the means whereby the increase in tractive adhesion is produced, and this result is attained in an entirely novel manner. Several attempts have heretofore been made to utilize magnetism for this purpose, but apparently without success, chiefly because of the crude and imperfect manner in which most of these attempts have been carried out.
The present system owes its efficiency to the formation of a complete and constantly closed magnetic circuit, moving with the vehicle and completed through the two driving axles, wheels, and that portion of the track rails lying between the two pairs of wheels, in a manner similar to that employed in the electrical method before shown. We have here a model of a second motor car equipped with the apparatus, mounted on a section of track and provided with means for measuring the amount of tractive force exerted both with and without the passage of the current.