<P> It was later shown by Howard Percy Robertson (1949) and others (see Robertson--Mansouri--Sexl test theory), that it is possible to derive the Lorentz transformation entirely from the combination of three experiments . First, the Michelson--Morley experiment showed that the speed of light is independent of the orientation of the apparatus, establishing the relationship between longitudinal (β) and transverse (δ) lengths . Then in 1932, Roy Kennedy and Edward Thorndike modified the Michelson--Morley experiment by making the path lengths of the split beam unequal, with one arm being very short . The Kennedy--Thorndike experiment took place for many months as the Earth moved around the sun . Their negative result showed that the speed of light is independent of the velocity of the apparatus in different inertial frames . In addition it established that besides length changes, corresponding time changes must also occur, i.e. it established the relationship between longitudinal lengths (β) and time changes (α). So both experiments do not provide the individual values of these quantities . This uncertainty corresponds to the undefined factor φ (\ displaystyle \ phi) as described above . It was clear due to theoretical reasons (the group character of the Lorentz transformation as required by the relativity principle) that the individual values of length contraction and time dilation must assume their exact relativistic form . But a direct measurement of one of these quantities was still desirable to confirm the theoretical results . This was achieved by the Ives--Stilwell experiment (1938), measuring α in accordance with time dilation . Combining this value for α with the Kennedy--Thorndike null result shows that β must assume the value of relativistic length contraction . Combining β with the Michelson--Morley null result shows that δ must be zero . Therefore, the Lorentz transformation with φ = 1 (\ displaystyle \ phi = 1) is an unavoidable consequence of the combination of these three experiments . </P> <P> Special relativity is generally considered the solution to all negative aether drift (or isotropy of the speed of light) measurements, including the Michelson--Morley null result . Many high precision measurements have been conducted as tests of special relativity and modern searches for Lorentz violation in the photon, electron, nucleon, or neutrino sector, all of them confirming relativity . </P> <P> As mentioned above, Michelson initially believed that his experiment would confirm Stokes' theory, according to which the aether was fully dragged in the vicinity of the earth (see Aether drag hypothesis). However, complete aether drag contradicts the observed aberration of light and was contradicted by other experiments as well . In addition, Lorentz showed in 1886 that Stokes's attempt to explain aberration is contradictory . </P> <P> Furthermore, the assumption that the aether is not carried in the vicinity, but only within matter, was very problematic as shown by the Hammar experiment (1935). Hammar directed one leg of his interferometer through a heavy metal pipe plugged with lead . If aether were dragged by mass, it was theorized that the mass of the sealed metal pipe would have been enough to cause a visible effect . Once again, no effect was seen, so aether - drag theories are considered to be disproven . </P>

Why was it important that the apparatus in the michelson and morley experiment could rotate