A right circular cylinder, open at the top, is filled with a liquid of specific gravity 1.2, and rotated about its vertical axis at such a speed that half of the liquid spills out. The gauge pressure at the centre of the bottom is
1
Zero
2
One-fourth of its value when the cylinder was full
3
One-third of its value when the cylinder was full
4
Three-fourth of its value when the cylinder was full