Temperature is read by measuring the liquid in the thermometer using the scale on the thermometer. when the temperature rises, the liquid in the thermometer . when the temperature drops, the liquid in the thermometer .

When the temperature rises, the liquid in the thermometer expands. When the temperature drops, the liquid in the thermometer contracts.

Explanation:

The thermometer is filled with a liquid called mercury. Increase in temperature makes this liquid to expand. The expanded liquid occupies most of the space in the thermometer causing a rise in its level.

On the other hand, a drop in temperature makes the liquid to contract. The contracted liquid has less volume and occupies lesser space in thermometer. This causes a drop in the level of liquid in thermometer.  

helicase, i think thats it