▁ ▁Stud ▁contact ▁ ▁The ▁prede cess ors ▁of ▁A PS ▁( known ▁as ▁stud ▁contact ▁systems ) ▁were ▁developed ▁around ▁ 1 9 0 0 , ▁and ▁used ▁by ▁several ▁tram way ▁companies ▁in ▁Paris ▁and ▁in ▁England . ▁Associ ated ▁with ▁these ▁systems ▁were ▁the ▁invent ors ▁Dol ter ▁and ▁Di atto . ▁ ▁There ▁were ▁two ▁main ▁differences ▁from ▁A PS : ▁ ▁Power ▁was ▁supplied ▁not ▁from ▁rails ▁but ▁from ▁stud s , ▁set ▁in ▁the ▁road ▁at ▁intervals ▁ ▁Switch ing ▁in ▁of ▁the ▁contacts ▁was ▁done ▁by ▁strong ▁elect romagnet s ▁beneath ▁each ▁car . ▁Each ▁contact ▁contained ▁a ▁f use , ▁which ▁would ▁be ▁blow n ▁by ▁an ▁earth ed ▁safety ▁sh oe ▁on ▁the ▁rear ▁of ▁the ▁tram ▁should ▁the ▁contact ▁not ▁have ▁switched ▁out . ▁This ▁proved ▁to ▁be ▁uns atisf actory ▁because ▁the ▁strong ▁curr ents ▁m elt ed ▁down ▁the ▁switch ▁contacts , ▁resulting ▁in ▁contacts ▁frequently ▁remaining ▁' live '. ▁ ▁Prag ue ▁ ▁In ▁Prag ue , ▁a ▁ground - level ▁power ▁supply ▁was ▁applied ▁at ▁the ▁experimental , ▁recre ational ▁and ▁prom ot ional ▁tram ▁line ▁operated ▁by ▁the ▁Czech ▁invent or ▁and ▁entrepr ene ur ▁Fr anti š ek ▁K ři ží k ▁at ▁Let ná ▁hill . ▁It ▁was ▁the ▁first ▁elect r ically - power ed ▁tram ▁line ▁in ▁the ▁Prag ue ▁ag gl omer ation . ▁The ▁track ▁was ▁operated ▁between ▁ 1 8 9 1 – 1 9 0 0 ; ▁however ▁the ▁ground