Abstract: A tennis ball support device is disclosed which is adapted to hold a tennis ball in mid-air without any contact thereof by the blowing of air from underneath. This device includes a housing having side walls being generally cylindrical and a top and bottom. A blower is positioned securely with respect to a mounting platform generally centrally within the housing and the housing defines apertures for receiving and expelling air therefrom. An outlet controlling device is affixed to the upper end of the housing within the outlet aperture to control the distance and speed of upwardly moving air used to support a tennis ball. The devices within the support device are resiliently mounted or insulated with respect to one another such as to minimize sound transmission between parts of the support device to provide a quietly functioning design. Also insulation is used throughout the chamber defined within the housing to further minimize noise and vibration.

Abstract: Apparatus for measuring the metacentric height of a vessel by the use of an electrical signal generator which may be an armature stabilized relative to earth by a pendulus precision gyro and a stator fixed to the vessel to provide alternately polarized signals as the vessel rolls in response to even small roll inducing forces, such as wind, harbor waves, etc. A charge is allowed to build up on a capacitor in response to a first polarized signal as the vessel rolls in one direction and be discharged from the capacitor in response to a second polarized signal as the vessel rolls in the opposite direction to produce a signal representative of total roll period which signal actuates an indicator calibrated in terms of metacentric height.