A DATE WITH DENSITY
'(<a href="http://www.j-archive.com/media/2007-03-14_J_28.jpg" target="_blank">Cheryl of the Clue Crew demonstrates a scientific instrument</a>.)  <a href="http://www.j-archive.com/media/2007-03-14_J_28a.jpg" target="_blank">This</a> device for measuring the density of liquids takes its name from the Greek for "water measure"'
hydrometer