Question

what is the principal behind a mercury barometer

Answer 1

The mercury barometer works on the principle of balancing the weight of a column of air by the weight of a column of mercury. The weight of the column of air pressing down on the mercury in the cistern is equal to the weight of the mercury which has been pushed up the measuring tube by that air pressure on the mercuty.

Answer 2

The mercury barometer works on theprinciple of balancing the weight of a column of air by the weight of a column of mercury. The weight of the column of air pressing down on themercury in the cistern is equal to the weight of the mercury which has been pushed up the measuring tube by that air pressure on the mercury...