Automatically operated switches for controlling supercharger change-speed levers at different altitudes, all being for use in aircraft mechanisms; thermostatically operated switches and thermostats, all for use in aircraft mechanisms; thermostatically operated apparatus for controlling the temperature of the air flow to the cooling and oil systems of aircraft engines; valves for measuring the temperature of the fuel mixture in aircraft engines and for controlling the amount of heating fluid passed through the heat exchanger; and barometric capsules, being instruments for fitting into aircraft mechanisms to overcome atmospheric pressure