SENSORY ORGANS ANATOMY. 1  Sensory organs are very highly developed and specialized organs that are an extension of the central nervous system, with a sole function to take in information and relate it to the brain. The sensory neurons are highly adapted to detect changes of both external and internal changes in the environment and report these changes to the brain.
If you break a mercury thermometer or light bulb, a small amount of liquid mercury may spill out. Liquid mercury can separate into small beads, which can roll some distance away. The mercury may also evaporate into vapour. However, this small amount of mercury is extremely unlikely to cause problems for your health.
Hence, the slightest change in temperature is notable when it's used in a thermometer. This is the reason behind mercury being used in thermometer. Some of the principles of the thermometer were known to Greek philosophers of two thousand years ago. The modern thermometer gradually evolved from the thermoscope with the addition of a scale in the early 17th century and standardisation through the 17th and 18th centuries.