Sentence:  It was with the assistance of one of the <WSD>members</WSD> of this expedition , Lauritz Esmarch , that Oersted succeeded in producing light by creating an electric discharge in mercury vapor through which an electric current was made to flow . 
Meaning of the word marked with <WSD> tags:  one of the persons who compose a social group (especially individuals who have joined and participate in a group organization)