Sentence:  The moſt celebrated <WSD>gnomons</WSD>, for examining the courſe of the ſun, which are exiſting at this time, have been ſuppoſed to be that in the church of St "Petronio" at "Bologna", 89 "Engliſh" feet high; that of the "Chartreux" at "Rome", about 67 feet; and that of St "Sulpice" at "Paris", 86 feet. ... [T]he <WSD>gnomon</WSD> of the cathedral of that city [Florence], erected by w:Paolo dal Pozzo Toscanelli 
Meaning of the word marked with <WSD> tags:  An object such as a pillar or a rod that is used to tell time by the shadow it casts when the sun shines on it, especially the pointer on a sundial. (from mid 16th c.)