The density of a liquid is to be determined by an old diameter cylindrical hydrometer whose division marks are completely wiped out. The hydrometer is first dropped in water of density , and the water level is marked. The hydrometer is then dropped into the other liquid, and it is observed that the mark for water has risen above the liquid-air interface. If the height of the watermark is , determine the density of the liquid. Note: Treat the hydrometer as being perfectly cylindrical.