Every-day Science: Volume 7. The Conquest of Time and Space

by Henry Smith Williams; Edward Huntington Williams

Now we are prepared to understand the Brennan gyroscope, which consists essentially of two such gyrostats as that shown in our diagram A, set into the frame of the car on the axis D E, their wheels revolving in opposite directions and their outer frames so linked together that when one turns in one direction on its axis D E, the other must turn in the opposite direction. As the sole object of having two of the gyroscopes is to facilitate the going around curves, we may for the moment neglect the second one, and consider the action of only one of the pair.

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.

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.

The thrust will cause the car to topple to the left and this will free the roller R₂, but a moment later it will bring the segment G₂ in contact with roller R₂ which thus receives an upward thrust. But an upward thrust, we recall, will not cause the spindle to move upward, but off to the right toward C; and so, a moment later still the roller R₂ will pass beyond the end of the segment G₂ and the roller R₁ will come in contact with the segment G₃, along which it will tend to roll, thus accelerating the precession to the right, and so causing the spindle to push downward, bringing the car back to its old position or beyond it; whereupon the segment G₄ will be brought in contact with R₂, retarding the further oscillation of the car and causing the spindle to move back again to the left.

This sequence of oscillations will be repeated over and over so long as any disturbing force tends to throw the car out of equilibrium. In other words, the gyroscope, when its balance is disturbed by a thrust due to any unbalancing of the car, will begin to wabble and continue to wabble until it finds a position where it is no longer disturbed, and this new position will be attained only when the car as a whole is perfectly balanced again.

In this new position of balance, the car (owing to a shift of its load or to the force of the wind) may be tipped far over to one side, as a man leans in carrying a weight on one shoulder, to get the centre of gravity over the rail, and in that event the axis of the gyroscope will be no longer horizontal. But that is quite immaterial. There is no more merit in the horizontal position than in any other, as regards the tendency to keep a fixed axis. If it is usually horizontal, this is only because under normal conditions the car will be balanced at its physical centre, just as ordinarily a man stands erect and does not lean to one side in walking.

Reverting for a moment to our diagram and the explanation just given, it will be understood that the two rollers R₁ and R₂ are never in action at the same time, and that it is only the roller R₁ that gives the sidewise push that accelerates the precession (since R₂ is not in contact with the axle itself).