Gyrus (anatomy)

“ The gyroscope is, as everyone knows, a top, and I might have called the hat I invented a top hat, except that any tall cylindrical silk or beaver hat is called a top hat, so I was forced to adopt the name of gyro-hat.
A gyroscope is not an ordinary top. It is like a heavy fly wheel, revolving on an axis; and if it is spun, the speed of the revolutions maintains the axis in the perpendicular. A huge gyroscope is used to steady the channel steamers, which would otherwise stagger and reel. ”

“ All the world has learned to call them gyroscopes. The vehicle that they balance may conveniently be termed a gyrocar—a name that has the sanction of the inventor himself.
Let it be understood once for all that a gyroscope is merely a body whirling about an axis. A top such as every child plays with is a gyroscope; a hoop such as every child rolls is a gyroscope; the wheels of bicycles, carriages, or railway-cars are gyroscopes; and the earth itself, whirling about its axis, is a gyroscope. You can make a gyroscope of your own body if you choose to197 whirl about, like a ballet-dancer. ”

“ In a word, the gyroscope is the most common thing imaginable. Indeed, if I wished to startle the reader with a seeming paradox, I might say without transcending the bounds of truth that, in the last analysis, there is probably nothing known to us in the universe but an infinitude of gyroscopes—atoms and molecules at one end of the scale; planets and suns at the other—all are whirling bodies. ”

“ With these two weights, the only possible position of equilibrium is on the meridian with its spin axis horizontal.
To make the gyro seek north, a system of reservoirs filled with mercury, known as mercury ballistics, is used to apply a force against the spin axis. The ballistics, usually four in number, are placed so that their centers of gravity exactly coincide with the CG of the gyroscope. Precession then causes the spin axis to trace an ellipse, one ellipse taking about 84 minutes to complete. (This is the period of oscillation of a pendulum with an arm equal to the radius of the earth.) ”

“ We may imagine that neither of them has any internal heat; so that the internal energy of each is the minimum that corresponds to its steady gyrostatic momentum, and the axis of each gyrostat therefore keeps a fixed direction in space. The result of the encounter will be that the axis of each gyrostat acquires steady wobbling or free processional motion, so that its internal energy is increased at the expense of the energy of translation of the atoms ”

“ The compass needle is virtually insulated from the terrestrial magnetism by the surrounding steel hull. But, fortunately, the gyroscope may be used as a compass and it is in no way affected by magnetism. Once the gyroscope is set spinning with its axis pointing to the North Pole of the heavens it will continue to point in that direction no matter how devious a course the vessel may pursue. If pointed in some other direction, the precessional forces set up by the rotation of the earth will turn it due north. ”

“ Foucault’s gyroscope. the preponderance is made zero, and the axis points to the pole, when free to move in the meridian.
Generally, if constrained to move in any other plane, the axis seeks the position nearest to the polar axis, like a dipping needle with respect to the magnetic pole. (A gyrostatic working model of the magnetic compass, by Sir W. Thomson. British Association Report, Montreal, 1884. A. S. Chessin, St Louis Academy of Science, January 1902.)
A spinning top with a polished upper plane surface will provide an artificial horizon at sea, when the real horizon is obscured. ”

“ Robert explained, “is automatically controlled by a delicate device attached to the central upright gyroscope.”
“I was under the impression that the entire apparatus was unaffected by gravity.”
“This device is the exception. The Sphere’s weight is neutralized to an absolute minimum by the gyroscopic control, but it was necessary to maintain one point of gravitational contact in order to establish some permanent upright stability; otherwise, the Sphere would revolve at random when in midair.” ”

“ When a gyroscope is spun at a very high velocity on a vertical axis, with the point of support very much above the center of gyration, it has a tendency to maintain a vertical axis; a horizontal or swinging motion of its support will not cause it to swing like a pendulum. ”

“ Again, it is curious to observe how an old and familiar truth, coming up in a new form, startles us as an impossible paradox. I well remember some twenty-five years ago, when the little instrument the gyroscope first made its appearance, how it startled everybody by its seeming violation of the laws of gravity. Imagine a heavy brass wheel rotating rapidly at one end of an axle, while the other end is supported on a vertical column. ”

“ Under such circumstances the gyroscope—though it continues to spin as hard as ever—has no effect whatever in preventing the rolling of the ship; it stands there, like the strong man bound, expressing its discontent with an angry groan. ”

“ The balancing action of the gyroscope seems no whit less remarkable after it is explained. It should be said, however, that the force exerted by the mechanism is not213 so tremendous as might at first thought appear, for the gyroscopes are by no means called upon to counteract the entire force of gravity brought to bear on the car. They do not in any sense lift the car; they only balance its two sides, which when left to themselves are approximately of equal weight. ”

“ A gyroscopic fly-wheel will preserve its original direction in space only when left absolutely free in all directions, as required in the experiments above. If employed in steering, as of a torpedo, the gyroscope must act through the intermediary of a light relay; but if direct-acting, the reaction will cause precession of the axis, and the original direction is lost.
The gyrostatic principle, in which one degree of freedom is suppressed in the axis, is useful for imparting steadiness and stability in a moving body ”

“ In fact the precession of the earth is of the same nature as that of this large gyrostat (Fig. 22) , which is suspended in gymbals, so that it has a vibration like a pendulum when not spinning. I will now spin it, so that looked at from above it goes against the hands of a watch, and you observe that it precesses with the hands of a watch. Here again is a hemispherical wooden ship, in which there is a gyrostat with its axis vertical. It is in stable {81}equilibrium. ”

“ A gyroscope has just been adopted to the monorail cars, and so long as the gyroscope gyrates the monorail car cannot stagger or reel. If a proper gyroscope was placed on the end of a knitting needle and gyrated at full speed, that knitting needle could be stood on end and it would not fall over.
Therefore, if a gyroscope was placed in the top of a top hat, and the top hat firmly fastened to the head of a man, and the gyroscope set going, that man would9 remain perpendicular in spite of anything. ”

“ In principle the action of this wheel is not different from that of an ordinary top on your table which wabbles221 to the right or to the left when you push its axis straight away from you. Yet to the untechnical observer it seems as if the Schlick gyroscope were a living thing, governed by almost human motives. If you apply a brake to prevent the longitudinal oscillations of the gyroscope, the effect, even though the fly-wheel still revolves at full speed, is precisely as if you pinioned the arms of a strong man, so that he saw the futility of resistance and made no struggle to free himself. ”

“ But it is spinning, and so it precesses. If gravity were greater it would precess faster, and it comes home to us that it is this precession which enables the force of gravity to be inoperative in mere downward motion. You see that if the precession is hurried, it is more than sufficient to balance gravity, {46}and the gyrostat rises. If I retard the precession, it is unable to balance gravity, and the gyrostat falls. If I clamp this vertical axis so that precession is impossible, you will notice that the gyrostat falls just as if it were not spinning. ”

“ It has indeed been entitled the paradox of mechanics; for though it depends on gravitation, gravitation yet appears indifferent to it. In order to render the operation of the Gyroscope as continuous as possible, so as to facilitate the profound study of its working, and also to unite another influence with those of the ordinary Gyroscope, producing phenomena of which this instrument affords us the spectacle, a learned American has employed electricity as a motive power. ”

“ In his mind he pictured the tiny gyroscopes all brought into alignment by the interplay of magnetic forces; and around each proton the tiny, planetary electrons.
Yet it was very well to think of the proton nucleus of the hydrogen atom as a simple top, he reminded himself; but they were more complex than that. Each orbiting electron must also contribute something to the effect.
At that point, Mike remembered, the electron itself would be spinning, a lighter-weight gyroscope, much as Earth has a lighter weight than the Sun. The electron, too, had a magnetic field ”

“ 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. ”

“ THE Brennan monorail car and the Schlick device for the prevention of rolling of ships at sea have recently attracted popular attention to the gyrostat, and gyrostatic action has recently become vitally interesting to a large group of men because an automobile-engine fly-wheel shows serious gyrostatic reactions when the automobile rounds a curve rapidly or rises suddenly upon a bump in the road. ”

“ In all our examples the slower the spin the quicker is the precession produced by given tilting forces.
Now close observation will give you a simple rule about the behaviour of a gyrostat. As a matter of fact, all that has been incomprehensible or curious disappears at once, if instead of speaking of this gyrostat as moving up or down, or to the right or left, I speak of its motions about its various axes. It offers no resistance to mere motion of translation. But when I spoke of its moving {40}horizontally, I ought to have said that it moved about the vertical axis A B (Fig. 13) . ”

“ What we require, therefore, is an erector which will respond slowly but surely to the average acceleration, which is downward, but too sluggishly to be affected by the shorter period accelerations due to turns or rolls. Slowness of response is a matter of the erecting forces being small and of the mass and angular velocity of the gyro disc being large. The success of the compromise called for depends on the relative times taken for the gyroscope to tilt seriously from the true vertical, due to the causes above mentioned, and for the average turn or roll. ”

“ I was dying for sleep, and my wife tumbled me into bed and pulled the sheet over me, and that same instant I fell into a heavy slumber, but the moment my wife released her grasp on me I began arising to my feet, irresistibly drawn to the perpendicular by the action of the gyro-hat. I continued to arise until I was standing upright. I can only liken the manner in which I arose to the way a man might raise a stiff arm slowly until it pointed straight upward. ”

“ It is believed by many aviators that the problem of automatic stability will be solved by some form of the gyroscope. A great many experiments are being made with various forms of the gyroscope, although no machine has as yet been actually fitted and flown with such a device. The general principle of the gyroscope is very simple. It consists of a wheel which is made to revolve at very high speed. When such a wheel turns fast enough it will remain in a fixed position. Every one is familiar for instance with the gyroscope top. ”

“ 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. ”

“ One of the most remarkable recent developments of the gyroscope is its use as a stabilizer in ships to keep them from rolling in a heavy sea. A comparatively small wheel is mounted in the hold of the vessel with perfect freedom to turn in any direction. If the wheel is clamped so that it cannot precess, the vessel will roll and pitch, but the instant the gyroscope is released it exerts its wonderful powers. ”

“ What we have already seen has made it clear that the revolving wheel of the Schlick gyroscope, to be effective, must bear an appreciable relation to the mass of the entire ship. Such a weight, revolving at a terrific speed and oscillating like a tremendous pendulum, obviously represents an enormous store of energy. ”

“ Thus if the point of the gyrostat is made to take the periodic motion given by λ = R exp nti, ζ = 0, the forced vibration of the axis is given by ῶ = P exp nti, where
P { − (A + Ma2) n2 + Kn + gMa} − RMn2a = 0;
(17) and so the effect may be investigated on the Fleuriais gyroscopic horizon of the motion of the ship.
Suppose the motion λ is due to the suspension of the gyrostat from a point on the axis of a second gyrostat suspended from a fixed point. ”