A vacuum pump is connected to the T - clip and some air is sucked out. The clip is then closed. The pressure inside the glass tubes falls and the liquids rise up the tubes. The liquids rise until the pressure due to each liquid column is equal to the difference between atmospheric pressure and the pressure P inside the glass tube. To measure the hieghts of the liquids h-1 and h-2 accurately, bend a paperclip into an asymmetric U shape and attach it to the bottom of the ruler used to measure
and
Thenand
are
plus the readings on the ruler respectively.
The pressure at the base of liquid A is then
The pressure at the base of liquid B is then
Equating these gives
Hence