Abstract: The history of the phenomenon of unipolar induction is reviewed, and the unipolar induction experiment of Bartlett et al is analyzed which is considered to be conclusive. It is found that using iron pipe for magnetic screen in Bartlett＇s experiment is unreasonable, and therefore their experimental conclusion is questionable. A possible method to improve the experiment of Bartlett et al is proposed. So the controversy of theoretical explanations of unipolar induction is still an open question.

Key words: unipolar induction, moving and nonmoving magnetic line hypothesis, magnetic screen