Sentence:  He was thinking; but the glory of the song, the swell from the great <WSD>organ</WSD>, the clustered lights, […], the height and vastness of this noble fane, its antiquity and its strength—all these things seemed to have their part as causes of the thrilling emotion that accompanied his thoughts. 
Meaning of the word marked with <WSD> tags:  A musical instrument that has multiple pipes which play when a key is pressed (the pipe organ), or an electronic instrument designed to replicate such.