What measuring instrument was invented by Frederick Jones?

The correct answer is the thermostat. Frederick Jones is noted for his groundbreaking work in refrigeration technology, particularly the development of the first portable air-cooling unit, which led to advancements in temperature control mechanisms. The thermostat is crucial in regulating temperature in various applications, such as in automotive and home heating systems. This innovation allowed for more efficient temperature management, highlighting Jones's impact on modern technology.

Thermostats function by sensing temperature changes and switching on or off heating or cooling systems to maintain a desired temperature range. The significance of Jones's invention lies in its practical application, revolutionizing how environments can be effectively controlled for comfort and preservation.

The other options do not align with Jones's contributions. A barometer measures atmospheric pressure, a thermometer measures temperature, and a hygrometer measures humidity levels. None of these instruments are attributed to Jones, as his primary focus was on refrigeration and temperature control technology.