Measuring aether Physics theories of the late 19th century postulated that , just as water waves must have a medium to move across -LRB- water -RRB- , and audible sound waves require a medium to move through -LRB- such as air or water -RRB- , so also light waves require a medium , the `` luminiferous aether '' .

Since waves in water need something to move in -LRB- water -RRB- and sound waves do as well -LRB- air -RRB- , it was believed that light also needed something to move in .
