Sentence:  The sequence of events leading to his important discovery still remains ambiguous but it seems that one of the advanced students at the university related that the first direct event that led to the publication of Oersted 's discovery occurred during a private <WSD>lecture</WSD> made before a group of other advanced students in the spring of 1820 . 
Meaning of the word marked with <WSD> tags:  a speech that is open to the public