▁he ▁incorpor ated ▁it ▁on ▁some ▁locomot ives ▁he ▁built ▁or ▁re built , ▁particularly ▁on ▁the ▁Mar iet ta ▁and ▁C inc inn ati ▁Rail road ▁and ▁later ▁the ▁Pennsylvania ▁Rail road . ▁ ▁John ▁H . ▁Wh et stone ▁of ▁C inc inn ati , ▁working ▁for ▁N iles ▁and ▁Company , ▁was ▁the ▁next ▁to ▁dev ise ▁a ▁method ▁for ▁equal izing ; ▁in ▁this ▁scheme , ▁the ▁tr uck ▁frame ▁was ▁itself ▁the ▁equal izing ▁beam ▁as ▁well . ▁ ▁N iles ▁went ▁bank rupt ▁before ▁the ▁pat ent ▁was ▁granted , ▁and ▁no ▁locomot ive ▁was ▁ever ▁fitted ▁with ▁this ▁design . ▁ ▁A ▁more ▁successful ▁scheme ▁for ▁equal izing ▁the ▁p ony ▁tr uck ▁to ▁the ▁drivers ▁was ▁invent ed ▁by ▁William ▁S . ▁Hudson , ▁super int endent ▁of ▁the ▁Rog ers ▁Lo comot ive ▁and ▁Machine ▁Works , ▁and ▁pat ented ▁in ▁ 1 8 6 4 . ▁ ▁In ▁this ▁design , ▁a ▁large ▁equal izing ▁lever ▁linked ▁the ▁front ▁tr uck ▁with ▁a ▁trans verse ▁bar ▁connected ▁to ▁the ▁front ▁spring ▁h angers ▁of ▁the ▁driving ▁whe els . ▁ ▁This ▁design ▁was ▁an ▁immediate ▁success ▁and ▁was ▁used ▁on ▁American - built ▁locomot ives ▁until ▁the ▁end ▁of ▁steam ▁building . ▁ ▁Term in ology ▁In ▁the ▁US , ▁these ▁tr uck s ▁were ▁known ▁as ▁lead ▁tr uck s . ▁ ▁A ▁p ony ▁tr uck ▁was ▁the ▁lead ▁tr uck ▁on ▁a ▁horse ▁drawn ▁rail ▁car ▁or ▁t rol ley