for example the liquid contained within the bulb on the common bulb thermometer of figure 1.2 exchanges energy with its surroundings until the two are in thermal equilibrium. At that point they are at the same temperature. This energy exchange is the input signal to this measurement system. The phenomenon of thermal expansion of the liquid results in its movement up and down the stem. Which in this case is the output signal from which we determine temperature. The liquid in the bulb acts as the sensor. By forcing the expanding liquid into a narrow capillary. This measurement system transforms thermal information into a mechanical displacement. Hence. The bulb’s internal capillary design acts as a transducer.