The Simple Usefulness of the Secchi Disc | Science History Institute

“In 1865 Pope Pius IX decided he needed more accurate measurements of the turbidity of the Mediterranean Sea. His reasons were disputed even at the time—some sources say he wanted to measure water pollution in and around the Mediterranean; others that he wanted more reliable navigational charts; while still others maintained that he simply wanted written proof of the beauty and clarity of the sea’s waters. Whatever the reason, Pius IX wanted turbidity measurements standardized.”