GYROSCOPES

and GYROSTATS are fnstruments by means of which the dynamics of a rotating body such as the earth or a spinning-top have been investigated. In the Gyroscope, invented towards the end of the 18th cent., the principal axis of rotation always pa es through a fixed point, and accordingly the rotating wheel or disk is mounted in gimbals. The Gyrostat was invented Er Kelvin to illustrate the movement of a rotating body left free to wander about on a horizontal plane. It illustrates the action of a top spun on a tablo When the gyroscope is rotated at a very high speed it resists any forces coming from without and tending to change its axis of rotation. Hence it can be used to give stability to a moving body through its inertia. The moment of wera can be calculated, and is equal, to the product of the ma of each: particle of the body into the square of its distance from the axis of rotation. It will, therefore, to some extent depend on the geometrical shape of the body. The radius of gyration of a rotating body is the distance from the axis of rotation at which, if the whole ma of the body were concentrated there, the energy of rotation of the body would be the same as it really is. The first practical application of the gyroscope was Sersen’s apparatus for providing a false horizon at sea when the real one was obscured by fog. It consisted of a top with a highly polished upper plane surface. Centrifugal machines, cream separators, are really tops held in a frame and obliged to rotate about a vertical axis—(7.e.,) they are an application of the gyrostatic principle in which one degree of freedom is suppre ed. Other modifications of this principle are used on the platforms of quick-firing guns and for searchlights on board ships. A gyroscopic fly-wheel travels in its original direction only, when it is perfectly free in all directions in space. In the form of a small heavy wheel fixed in gimbals rotating at at least 2,000 revolutions per minute it is used to control the course of a torpedo or submarine. The fly-wheel acts on a valve to which rudders are attached. The rolling of a ship can be neutralized by the presence of a gyrostat the movement of which is restrained in one direction, and the same principle can he used to give stability to a mono-rail car. | In 1911 the gyroscopic compa was invented, and the gyroscope was used Bicycle wheels furnish an instance of gyrostatic movement. Any deviations from the original direction of the movement can be corrected by forces of the required direction acting through the handle-bars. Many complicated composite movements can be explained by the fact that, given forces acting in the proper direction, it is po ible to overcome the inertia due to gyrostatic movement. The earth can be considered as a large top with a slow backward motion of the equinoctial points due to the attractive force by the sun, moon, and planets. The axis of the earth describes in space a conical motion in about 26,000 years. Various applications of the gyroscope have been used to demonstrate the inclination of the earth’s] axis. Large gyroscopes installed ocean ve els are found to stabilize| the motion and to prevent seasickne . in|seaport town of ancient Greece, on’ Gulf of Laconia; was Spartan naval) | station; now mostly submerged. _ H, eighth letter of the Hing. alphabet; derived from the Phoenician, and “originally consisted of two upright and three transverse bars. It is an aspirate, or simple breath sound, neither con- ‘sonant nor vowel; sounded in words of ative origin, but in a few words de- ‘tived from the Latin, such as ‘hour’ and ‘honour,’ mute.