Poggendorff's illusion ポッゲンドルフの錯視 繝ｩ繧､繝輔し繧､繧ｨ繝ｳ繧ｹ
An optical illusion first described by the German scientist Johan Poggendorff in 1860. He observed that a diagonal line appears disjointed when it is intersected by two parallel lines.