Waxa uu sidoo kale xusay (sida Lorentz ee 1899) in mass this sidoo kale waxay ku xiran tahay jihada iyo abuurtay magacyada "Longitudinal" iyo "Transverse" Mass. Si ka duwan Lorentz, ma uu ku daray Contraction Hypothesis in uu aragtida, iyo sidaas daraaddeed shuruudaha mass uu ka duwan kuwa Lorentz. Iyada oo ku saleysan shaqada ka horeeyay on mass electromagnetic, Friedrich Hasenöhrl soo jeediyay in qayb ka mid ah mass ee jirka (kaas oo uu ku magacaabay mass muuqata) waxaa loo maleyn karaa sida shucaaca boodhka ku wareegsan. "mass muuqata" ee shucaaca ku xiran yahay heerkulka (maadaama uu jidhka soo saaray shucaaca) iyo waa u dhiganta tamarta muuqata.
heerkulka