▁During ▁his ▁development ▁of ▁Max well ' s ▁Theory , ▁J . ▁J . ▁Thom son ▁( 1 8 8 1 ) ▁recognized ▁that ▁charged ▁bodies ▁are ▁harder ▁to ▁set ▁in ▁motion ▁than ▁un charg ed ▁bodies . ▁Elect ro static ▁fields ▁behave ▁as ▁if ▁they ▁add ▁an ▁" elect romagnet ic ▁mass " ▁to ▁the ▁mechanical ▁mass ▁of ▁the ▁bodies . ▁I . e ., ▁according ▁to ▁Thom son , ▁elect romagnet ic ▁energy ▁corresponds ▁to ▁a ▁certain ▁mass . ▁This ▁was ▁interpreted ▁as ▁some ▁form ▁of ▁self - ind uct ance ▁of ▁the ▁elect romagnet ic ▁field . ▁He ▁also ▁noticed ▁that ▁the ▁mass ▁of ▁a ▁body ▁in ▁motion ▁is ▁increased ▁by ▁a ▁constant ▁quantity . ▁Thom son ' s ▁work ▁was ▁continued ▁and ▁perfect ed ▁by ▁Fitz G er ald , ▁He av is ide ▁( 1 8 8 8 ), ▁and ▁George ▁Frederick ▁Charles ▁S ear le ▁( 1 8 9 6 , ▁ 1 8 9 7 ). ▁For ▁the ▁elect romagnet ic ▁mass ▁they ▁gave   — ▁in ▁modern ▁notation   — ▁the ▁formula ▁, ▁where ▁ ▁is ▁the ▁elect romagnet ic ▁mass ▁and ▁ ▁is ▁the ▁elect romagnet ic ▁energy . ▁He av is ide ▁and ▁S ear le ▁also ▁recognized ▁that ▁the ▁increase ▁of ▁the ▁mass ▁of ▁a ▁body ▁is ▁not ▁constant ▁and ▁var ies ▁with ▁its ▁velocity . ▁Con sequently , ▁S ear le ▁noted ▁the ▁impos s ibility ▁of ▁super l um inal ▁veloc ities , ▁because ▁infinite ▁energy ▁would ▁be ▁needed ▁to