·          A solid slab is dipped in the liquid.

 ·          The slab is tilted with varying angles till the surface of the liquid becomes horizontal.

 ·          The angle between the slab & the horizontal liquid surface is measured.

 ·          It is the angle contact but we measured the external angle, then  ]   q = 180 – external angle.

 ·           In case of mercury in glass: the surface of the mercury becomes plan at one side & convex at the other side.

 ·          In case of water in glass: the surface of the water becomes plan at one side & concave at the other side.