▁fro . ▁The ▁experiment ▁was ▁sufficiently ▁precise ▁to ▁measure ▁ret ard ations ▁of ▁ ▁of ▁a ▁half ▁w avel ength , ▁i . e . ▁of ▁the ▁order ▁. ▁Depending ▁on ▁the ▁direction ▁relative ▁to ▁Earth ' s ▁motion , ▁the ▁expected ▁ret ard ation ▁due ▁to ▁b ire fr ing ence ▁was ▁of ▁order ▁ 1 0 − 8 , ▁which ▁was ▁well ▁within ▁the ▁accuracy ▁of ▁the ▁experiment . ▁Therefore , ▁it ▁was , ▁besides ▁the ▁Michel son - Mor ley ▁experiment ▁and ▁the ▁Tr out on – No ble ▁experiment , ▁one ▁of ▁the ▁few ▁experiments ▁by ▁which ▁magn itudes ▁of ▁second ▁order ▁in ▁v / c ▁could ▁be ▁detected . ▁However , ▁the ▁result ▁was ▁completely ▁negative . ▁Ray le igh ▁repeated ▁the ▁experiments ▁with ▁layers ▁of ▁glass ▁pl ates ▁( although ▁with ▁a ▁dimin ished ▁precision ▁by ▁a ▁factor ▁of ▁ 1 0 0 ), ▁and ▁again ▁obtained ▁a ▁negative ▁result . ▁ ▁However , ▁those ▁experiments ▁were ▁critic ized ▁by ▁De W itt ▁Br istol ▁Bra ce ▁( 1 9 0 4 ). ▁He ▁argued ▁that ▁Ray le igh ▁hadn ' t ▁properly ▁considered ▁the ▁consequences ▁of ▁contra ction ▁( ▁instead ▁of ▁ 1 0 − 8 ) ▁as ▁well ▁as ▁of ▁the ▁ref raction ▁index , ▁so ▁that ▁the ▁results ▁were ▁in ▁no ▁way ▁conclus ive . ▁Therefore , ▁Bra ce ▁conducted ▁experiments ▁of ▁much ▁higher ▁precision . ▁He ▁employed ▁an ▁appar atus ▁that ▁was ▁ 4 . 1 3 ▁m ▁long , ▁ 1 5