Our diagram 2, then, will represent one of Mr. Brennan's gyroscopes in action. It is pivoted into the framework of the car on the axis _D E_. If you examine it you will see that it is essentially the Foucault gyrostat of our other diagram, with the axis _O A_ projected beyond the frame to the point _F_. In practice, the frame _B A C_ is made to carry the field-magnet of an electric motor for spinning the wheel. But this in no wise affects the principles of action. Mr. Brennan's invention consists of the exceedingly ingenious way in which he applies these principles; and to understand this we must follow our diagram closely. Looking at it, you will see that the spindle _O F_ carries two rollers _R1_ and _R2_ which may come in contact under certain circumstances with the curved segment marked _G1_, _G2_, _G3_, _G4_, which are strong segments of the car-frame itself--the segments, indeed, upon which the force of the gyroscope is expended in holding the car in equilibrium. It must be understood further that the roller _R1_ is loosely fitted to the spindle _O F_ and hence can whirl with it when pressed against the segment _G1_ or _G3_; whereas the roller _R2_ is fitted about a non-revolving extension of the frame _B A C_, and not to the spindle itself. Bearing in mind that the gyroscope itself is perfectly balanced and hence tends to maintain its axis _O F_ in a fixed direction, we shall be able to understand what must happen when the car is tipped from any cause whatever--as the shifting of its load, the pressure of the wind, or the centrifugal action due to rounding a curve. [Illustration: FIG. 2.] Suppose, for example, that the car tips to the right. This will bring the segment _G1_ in contact with the roller _R1_, and the roller will instantly tend to run along it, as a car-wheel runs along the track, because friction with the spindle causes it to revolve. But this, it will be evident, is equivalent to pushing the spindle _F_ (or the frame _A_) toward _B_--"accelerating the precession"--and we know that the effect of such a push will be to cause the spindle (thanks to that round-the-corner action) to rise, thus pushing up the segment _G1_, and with it the car itself.