▁with ▁various ▁met all ic ▁rings ▁by ▁swing ing ▁the ▁need le ▁by ▁ 4 5 ° ▁and ▁counting ▁the ▁number ▁of ▁oscill ations ▁until ▁the ▁need le ▁dropped ▁to ▁ 1 0 ° ▁angle . ▁The ▁results ▁were ▁as ▁following : ▁ ▁Arag o ▁gave ▁this ▁phenomen on ▁the ▁name ▁of ▁magnet ism ▁of ▁rotation . ▁In ▁ 1 8 2 5 ▁was ▁published ▁a ▁further ▁experiment ▁where ▁he ▁observed ▁the ▁reaction ▁of ▁station ary ▁magnetic ▁need le ▁to ▁rot ating ▁co pper ▁disc . ▁ ▁Description ▁▁ ▁A ▁magnetic ▁need le ▁is ▁freely ▁susp ended ▁on ▁a ▁pivot ▁or ▁string , ▁a ▁short ▁distance ▁above ▁a ▁co pper ▁disc . ▁If ▁the ▁disk ▁is ▁station ary , ▁the ▁need le ▁align s ▁itself ▁with ▁the ▁Earth ' s ▁magnetic ▁field . ▁If ▁the ▁disc ▁is ▁rot ated ▁in ▁its ▁own ▁plane , ▁the ▁need le ▁rot ates ▁in ▁the ▁same ▁direction ▁as ▁the ▁disc . ▁( The ▁effect ▁decre ases ▁as ▁the ▁distance ▁between ▁the ▁magnet ▁and ▁the ▁disk ▁increases .) ▁ ▁Vari ations : ▁If ▁the ▁disk ▁is ▁free ▁to ▁rotate ▁with ▁minimal ▁fr iction , ▁and ▁the ▁need le ▁is ▁rot ated ▁above ▁or ▁below ▁it , ▁the ▁disk ▁rot ates ▁in ▁the ▁same ▁direction ▁as ▁the ▁need le . ▁( This ▁is ▁easier ▁to ▁observe ▁or ▁measure ▁if ▁the ▁need le ▁is ▁a ▁larger ▁magnet .) ▁If ▁the ▁need le ▁is ▁not ▁allowed ▁to ▁rotate , ▁its ▁presence ▁ret ards ▁rotation ▁of ▁the ▁disc . ▁( This ▁is