# Why in mercury barometer pressure inside the glass tube at a point is same as the pressure outside the glass tube at the same height?

I am quite familiar with the pascal’s law but i still think that being on the same points still they should have different pressures as above on one point is atmosphere and on the other is only the column of mercury can anyone give physical explanation for this and also if the pressure inside the torricelli vacuum is only due to mercury vapours which is quite low than why the vacuum does not get crushed under the atmospheric pressure?

• Atmospheric pressure is $1~kg/cm^2$. If the tube's surface area is $1cm^2$, it needs to be strong enough to not break when you put $1kg$ over it's entire surface. – AgentS Dec 2 '19 at 5:40

Now the pressure in the space above the mercury is less than atmospheric pressure and equilibrium is attained when $$Mg$$ (where M is the new mass of mercury which is less than initial mass in the mercury column) + P*A (where P is less than atmospheric pressure) = (Atmospheric pressure) $$A$$ where A is area of cross section of tube. Or as $$ρ g h$$ (where h is the new height of column) = P + Atmospheric pressure
So we get. $$\rho g h = P_\text{atm} - P$$
where $$\rho$$ is the density of the mercury.