the battery current until the saturation point of the iron is reached, the tractive force is increased nearly 200 per cent., as shown by the dynamometer.  A large portion of this resistance to the slipping or skidding of the driving wheels is undoubtedly due to direct magnetic attraction between the wheels and track, this attraction depending upon the degree of magnetic saturation and the relative mass of metal involved.

But by far the greatest proportion of the increased friction is purely the result of the change in position of the iron molecules due to the well known action of magnetism, which causes a direct and close interlocking action, so to speak, between the molecules of the two surfaces in contact.  This may be illustrated by drawing a very thin knife blade over the poles of an ordinary electro-magnet, first with the current on and then off.

In the model before you, the helices are fixed firmly to, and revolve with, the axles, the connections being maintained by brushes bearing upon contact rings at each end of the helices.  If desired, however, the axles may revolve loosely within the helices, and instead of the latter being connected for cumulative effects, they may be arranged in other ways so as to produce either subsequent or opposing magnetic forces, leaving certain portions of the circuit neutral and concentrating the lines of force wherever they maybe most desirable.  Such a disposition will prove of advantage in some cases.

The amount of current required to obtain this increased adhesion in practice is extremely small, and may be entirely neglected when compared to the great benefits derived.  The system is very simple and inexpensive, and the amount of traction secured is entirely within the control of the motor man, as in the electric system.  It will be seen that the car here will not, with the traction circuit open, propel itself up hill when one end of the track is raised more than 5 inches above the table; but with the circuit energized it will readily ascend the track as you now see it, with one end about 131/2, inches above the other in a length of three feet, or the equivalent of a 40 per cent. grade; and this could be increased still further if the motor had power enough to propel itself against the force of gravity on a steeper incline.  As you will notice, the motor adheres very firmly to the track and requires a considerable push to force it down this 40 per cent. grade, whereas with the traction circuit open it slips down in very short order, notwithstanding the efforts of the driving mechanism to propel it up.

The resistance of the helices on this model is less than two ohms, and this will scarcely be exceeded when applied to a full sized car, the current from two or three cells of secondary batteries being probably sufficient to energize them.