' s ▁ 1 8 8 1 - ex periment , ▁and ▁they ▁substantial ly ▁increased ▁the ▁accuracy ▁of ▁the ▁measurement . ▁However , ▁this ▁now ▁famous ▁Michel son – Mor ley ▁experiment ▁again ▁yield ed ▁a ▁negative ▁result , ▁i . e ., ▁no ▁motion ▁of ▁the ▁appar atus ▁through ▁the ▁a ether ▁was ▁detected ▁( although ▁the ▁Earth ' s ▁velocity ▁is ▁ 6 0   km / s ▁different ▁in ▁the ▁northern ▁winter ▁than ▁summer ). ▁So ▁the ▁phys ic ists ▁were ▁confront ed ▁with ▁two ▁seem ingly ▁contradict ory ▁experiments : ▁the ▁ 1 8 8 6 - ex periment ▁as ▁an ▁apparent ▁confirm ation ▁of ▁F res nel ' s ▁station ary ▁a ether , ▁and ▁the ▁ 1 8 8 7 - ex periment ▁as ▁an ▁apparent ▁confirm ation ▁of ▁Sto kes ' ▁completely ▁drag ged ▁a ether . ▁ ▁A ▁possible ▁solution ▁to ▁the ▁problem ▁was ▁shown ▁by ▁Wol dem ar ▁Vo igt ▁( 1 8 8 7 ), ▁who ▁investig ated ▁the ▁Do pp ler ▁effect ▁for ▁waves ▁propag ating ▁in ▁an ▁in com press ible ▁el astic ▁medium ▁and ▁dedu ced ▁transformation ▁relations ▁that ▁left ▁the ▁wave ▁equation ▁in ▁free ▁space ▁un changed , ▁and ▁explained ▁the ▁negative ▁result ▁of ▁the ▁Michel son – Mor ley ▁experiment . ▁The ▁Vo igt ▁transformations ▁include ▁the ▁Lor ent z ▁factor ▁ ▁for ▁the ▁y - ▁and ▁z - co ordinates , ▁and ▁a ▁new ▁time ▁variable ▁ ▁which ▁later ▁was ▁called ▁" local ▁time ". ▁However