A spinning top set down so that it stands at an angle to the floor will right itself; it will rise till it stands upright on the point of equal friction.  Brennan’s resource, therefore, was to treat his gyroscope as a top.  He enclosed it in a case, through which its axles projected, and at each side of the car he built stout brackets reaching forth a few inches below each end of the axle.

The result is not difficult to deduce.  When the car came to a curve, the centrifugal action tended to throw it outward; the side of the car that was on the inside of the curve swung up and the bracket touched the axle of the gyroscope.  Forthwith, in the manner of its father, the top, the gyroscope tried to stand upright on the bracket; all the weight of it and all its wonderful force were pressed on that side of the car, holding it down against the tendency to rise and capsize.  The thing was done; the spinning top had come to the rescue of its posterity.  It only remained to fit a double gyroscope, with the wheels revolving in opposite directions, and, save for engineering details, the mono-rail car was evolved.

Through the window in the back of the cab I was able to watch them at then; work—­not the actual gyroscopes, but their cases, quivering with the unimaginable velocity of the great wheels within, turning and tilting accurately to each shifting weight as the men on board moved here and there.  Above them were the glass oilcups, with the opal-green engine-oil flushing through them to feed the bearings.  Lubrication is a vital part of the machine.  Let that fail, and the axles, grinding and red-hot, would eat through the white metal of the bearings as a knife goes through butter.  It is a thing that has been foreseen by the inventor:  to the lubricating apparatus is affixed a danger signal that would instantly warn the engineer.

“But,” says Brennan, “if one broke down, the other gyroscope would hold her up—­till ye could run her to a siding, anyway.”

“But supposing the electric apparatus failed?” suggests a reporter—­with visions of headlines, perhaps.  “Supposing the motor driving the gyroscopes broke down; what then?”

“They’d run for a couple of days, with the momentum they’ve got,” answers the inventor.  “And for two or three hours, that ’ud keep her upright by itself.”

On the short track at Gillingham there are no gradients to show what the car can do in the way of climbing, but here again the inventor is positive.  She will run up a slope as steep as one in six, he says.  There is no reason to doubt him; the five-foot model that he used to exhibit could climb much steeper inclines, run along a rope stretched six feet above the ground, or remain at rest upon it while the rope was swung to and fro.  It would do all these things while carrying a man; and, for my part, I am willing to take Brennan’s word.