According to Jewish religious law, to make a public prayer (aloud) should meet a minimum of 10 adult males. This group is called "Minyan".
The tradition says that once, in a synagogue, there were nine adult males only, so that prayer could not be start and then, unexpectedly, apperead an unknown person allowed to complete the group, form the mjnyŠn and initiate the prayer.
† Conventional wisdom says that this was the tenth person Prophet Elias (Eliyahu) and since then, in the synagogues, reserves a special seat for the Prophet for some other time if their presence is necessary and has well presented.
The chair of the picture is on one of the "four Sephardic synagogues" in the Jewish Quarter of the Old City of Jerusalem.
Translated with Google Traslator. My level of English does not allow me to do the translation directly. Please excuse any errors.