▁to ▁. ▁But ▁unlike ▁the ▁fict it ious ▁quantities ▁introduced ▁by ▁Po inc ar é , ▁he ▁considered ▁it ▁as ▁a ▁real ▁physical ▁entity . ▁Abraham ▁also ▁noted ▁( like ▁Lor ent z ▁in ▁ 1 8 9 9 ) ▁that ▁this ▁mass ▁also ▁depends ▁on ▁the ▁direction ▁and ▁co ined ▁the ▁names ▁" Long itud inal " ▁and ▁" Trans verse " ▁Mass . ▁In ▁contrast ▁to ▁Lor ent z , ▁he ▁didn ' t ▁incorpor ate ▁the ▁Cont raction ▁Hyp oth esis ▁into ▁his ▁theory , ▁and ▁therefore ▁his ▁mass ▁terms ▁differ ed ▁from ▁those ▁of ▁Lor ent z . ▁ ▁Based ▁on ▁the ▁preceding ▁work ▁on ▁elect romagnet ic ▁mass , ▁Friedrich ▁Has en ö hr l ▁suggested ▁that ▁part ▁of ▁the ▁mass ▁of ▁a ▁body ▁( which ▁he ▁called ▁apparent ▁mass ) ▁can ▁be ▁thought ▁of ▁as ▁radiation ▁b oun cing ▁around ▁a ▁cav ity . ▁The ▁" app ar ent ▁mass " ▁of ▁radiation ▁depends ▁on ▁the ▁temperature ▁( because ▁every ▁he ated ▁body ▁em its ▁radiation ) ▁and ▁is ▁proportional ▁to ▁its ▁energy . ▁Has en ö hr l ▁stated ▁that ▁this ▁energy - app ar ent - mass ▁relation ▁only ▁holds ▁as ▁long ▁as ▁the ▁body ▁radi ates , ▁i . e ., ▁if ▁the ▁temperature ▁of ▁a ▁body ▁is ▁greater ▁than ▁ 0 ▁K . ▁At ▁first ▁he ▁gave ▁the ▁expression ▁ ▁for ▁the ▁apparent ▁mass ; ▁however , ▁Abraham ▁and ▁Has en ö hr l ▁himself ▁in ▁ 1 9 0 5 ▁changed ▁the