This is due to the fact that the change in air pressure is applied to the entire hydrometer flask; the submerged portion of the flask receives a transmitted force through the liquid, thus the flask receives no net force due to the change in air pressure.
The change in air pressure is applied to the entire hydrometer flask. This is due to the fact this. The submerged portion of the flask receives a transmitted force through the liquid. The flask receives no net force due to the change in air pressure.